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1、State of Global Water Resources 2023WMO-No.1362WEATHER CLIMATE WATERReportBWMO-No.1362 World Meteorological Organization,2024The right of publication in print,electronic and any other form and in any language is reserved by WMO.Short extracts from WMO publications may be reproduced without authoriza

2、tion,provided that the complete source is clearly indicated.Editorial correspondence and requests to publish,reproduce or translate this publication in part or in whole should be addressed to:Chair,Publications BoardWorld Meteorological Organization(WMO)7 bis,avenue de la Paix Tel.:+41(0)22 730 84 0

3、3P.O.Box 2300 Email:publicationswmo.intCH-1211 Geneva 2,Switzerland ISBN 978-92-63-11362-7Cover illustration from WMO 2020 Calendar Competition:“Reality is an illusion”by Rajit Banerjee,Pangong Lake,Ladakh,India.NOTEThe designations employed in WMO publications and the presentation of material in th

4、is publication do not imply the expression of any opinion whatsoever on the part of WMO concerning the legal status of any country,territory,city or area,or of its authorities,or concerning the delimitation of its frontiers or boundaries.The mention of specific companies or products does not imply t

5、hat they are endorsed or recommended by WMO in preference to others of a similar nature which are not mentioned or advertised.The findings,interpretations and conclusions expressed in WMO publications with named authors are those of the authors alone and do not necessarily reflect those of WMO or it

6、s Members.Give us your feedback!https:/ version of the reporthttps:/ of abbreviations.vExecutive summary.viForeword.ixIntroduction.1The backdrop:overview of climatic conditions in 2023.3Data sources .4Anomaly calculation.5River discharge.6Reservoirs.10Inflow into selected reservoirs .10Reservoir sto

7、rage.11Lakes .12Groundwater levels.13Soil moisture.16Observed soil moisture from the International SoilMoistureNetwork.16Modelled soil moisture.17Evapotranspiration.19Terrestrial water storage .21Case study on the water storage situation in Central Europe during 2023 .22Snow cover and glaciers.24Sno

8、w water equivalent.24Peak snow mass in North American basins.25Glaciers.25Glacier contribution to seasonal river runoff.25The year 2023 in context.27High-impact hydrological events.30Flooding in Libya.30Flooding in Democratic Republic of the Congo and Rwanda.30Flooding in the Horn of Africa.30Floodi

9、ng in Mozambique and Malawi.30Drought in Central America and the southern United States .32Drought in Argentina,Uruguay and Brazil.32Drought in Peru.32Flooding on the North Island of New Zealand.33Flooding in China and the Philippines.33Flooding in Italy .33Synthesis.34Endnotes.38Annex.Technical ann

10、ex .45iiWMO is grateful to the following contributors.WMO MEMBER STATES AND TERRITORIES THROUGH HYDROLOGICAL ADVISORS AND ASSIGNED FOCAL POINTS FOR THE STATE OF THE GLOBAL WATER RESOURCES REPORTArgentina;Armenia;Australia;Azerbaijan;Belgium;Belize;Benin;Bhutan;Botswana;Brazil;Bulgaria;Canada;China;C

11、osta Rica;Croatia;Cyprus;Czechia;Denmark;Egypt;El Salvador;Finland;France;Germany;Ghana;Guatemala;Honduras;Hong Kong,China;Hungary;Iceland;India;Iraq;Israel;Japan;Kazakhstan;Kenya;Republic of Korea;Latvia;Lesotho;Malawi;Mauritius;Republic of Moldova;Montenegro;Myanmar;Nepal;New Zealand;Nigeria;Norwa

12、y;Pakistan;Panama;Paraguay;Peru;Philippines;Poland;Russian Federation;Serbia;Singapore;Slovakia;Slovenia;South Africa;Sri Lanka;Sweden;Switzerland;United Republic of Tanzania;Thailand;Turkmenistan;United Kingdom of Great Britain and Northern Ireland;Uruguay;Uzbekistan;Viet Nam.Hydrological Advisors

13、and focal points contributed to and supported the preparation of the present report by providing observational data,information about major hydrological events that occurred in 2023 and other relevant information,and participated in the review and validation of the report.STEERING COMMITTEE MEMBERSJ

14、an Danhelka(Czechia,Vice-President of INFCOM);Harry Dixon(United Kingdom);Katie Facer-Childs(United Kingdom,HydroSOS Technical Team Lead);Mohamed Housseini Ibrahim(Niger,Chair of Hydrological Coordination Panel);Michel Jean(Canada,President INFCOM);Harry Lins(United States of America);Ian Lisk(Unite

15、d Kingdom,President SERCOM);Ilias Pechlivanidis(Sweden,Research Board);Marcelo Uriburu Quirno(Argentina,Vice-Chair of the Standing Committee on Hydrological Services);Yuri Simonov(Russian Federation,Chair of the Standing Committee on Hydrological Services);Narendra Tuteja(Australia,Chair of the Expe

16、rt Team on Operational Hydrological Prediction Systems);Andy Wood(United States,Expert Team on Operational Hydrological Prediction Systems).REGIONAL HYDROLOGICAL ADVISORSAngela Corina(Regional Association VI),John Fenwick(Regional Association V),Mohamed Housseini Ibrahim,Sung Kim(Regional Associatio

17、n II),Jean-Claude Ntonga(Regional Association I),Fabio Andres Bernal Quiroga(Regional Association III),and Jose Zuniga(Regional Association IV),who contributed to the preparation and review of the report.WMO EXPERTSExperts from the Standing Committee Climate,Standing Committee on Hydrological Servic

18、es,Standing Committee on Services for Agriculture,Study Group on Renewable Energy Transition,and former Joint Expert Team on Hydrological Monitoring,who participated in the preparation and review of the report.AcknowledgementsiiiMEMBERS OF THE GLOBAL HYDROLOGICAL MODELLING COMMUNITYJafet Andersson(S

19、wedish Meteorological and Hydrological Institute(SMHI),Berit Arheimer(SMHI),Hasnain Aslam(University of Tokyo),Nishan Kumar Biswas(NASA),Martyn P.Clark(University of Saskatchewan),Chris DeBeer(University of Saskatchewan),Mohamed Elshamy(Environment and Climate Change Canada(ECCC),Global Institute fo

20、r Water Security(GIWS)(University of Saskatchewan),Xing Fang(University of Saskatchewan),Angelica Gutierrez(National Oceanic and Atmospheric Administration(NOAA),Riley Hales(Brigham Young University(BYU),Shaun Harrigan(European Centre for Medium-range Weather Forecasts(ECMWF),Kristina Isberg(SMHI),R

21、ohini Kumar(Helmholtz Centre for Environmental Research UFZ),Sujay Kumar(National Aeronautics and Space Administration(NASA),Henrik Madsen(DHI),Christopher Marsh(University of Saskatchewan),Jim Nelson(BYU),Wanshu Nie(NASA),Emmanuel Nyenah(Goethe University Frankfurt),John Pomeroy(University of Saska

22、tchewan),Daniel Princz(ECCC,GIWS(University of Saskatchewan),Oldrich Rakovec(Helmholtz Centre for Environmental Research UFZ),Robert Reinecke(Johannes Gutenberg University Mainz),Jrgen Rosberg(SMHI),Luis Samaniego(Helmholtz Centre for Environmental Research UFZ),Hannes Mller Schmied(Goethe Universit

23、y Frankfurt,Senckenberg Leibniz Biodiversity and Climate Research Centre(SBiK-F),Frankfurt),Tricia Stadnyk(University of Calgary),Edwin H.Sutanudjaja(Utrecht University),Niko Wanders(Utrecht University),Albrecht Weerts(Deltares),Kosuke Yamamoto(Japan Aerospace Exploration Agency),Kei Yoshimura(Unive

24、rsity of Tokyo),and Xing Yuan(Institute of Atmospheric Physics,Chinese Academy of Sciences),who contributed to the initial discussions,report preparation,global modelling and remotely sensed data,feedback and review.GLOBAL DATA CENTRES AND EXTERNAL EXPERTSElie Gerges(International Groundwater Resour

25、ces Assessment Centre(IGRAC),Elisabeth Lictevout(IGRAC),Simon Mischel(Global Runoff Data Centre(GRDC),Arnaud Sterckx(IGRAC)and Matthias Zink(International Soil Moisture Network(ISMN),who supported the preparation of the report.We thank Jan Polcher(cole Polytechnique,France)for contributing to the pr

26、eparatory workshop for this report.We also thank the research groups of Stefan Kollet(Forschungszentrums,Juelich,Germany)and Nico Sneeuw(University of Stuttgart,Germany)for contributing a case study for the hydrological situation in Central Europe in 2023 and data sets for the extension of in situ r

27、iver discharge data through satellite observations,respectively.We are grateful to Jiawei Hou(Australian Bureau of Meteorology)for providing lake storage data from the Global Water Monitor.CONTRIBUTORS AND CO-AUTHORS FOR SPECIFIC CHAPTERSGroundwater Levels:Elie Gerges(IGRAC),Elisabeth Lictevout(IGRA

28、C),Arnaud Sterckx(IGRAC),who supported the preparation of the report and developed the methodology.Soil Moisture:Matthias Zink(ISMN),who contributed to the soil moisture chapter with in situ data and supported the drafting of the related section.Terrestrial Water Storage:Andreas Gntner and Eva Boerg

29、ens(German Research Centre for Geosciences(GFZ),who provided the terrestrial water storage data which form an important part of the present report.Snow Cover and Glaciers:Ins Dussaillant(World Glacier Monitoring Service(WGMS),University of Zurich,Switzerland),Lawrence Mudryk(ECCC)and Michael Zemp(WG

30、MS,University of Zurich,Switzerland),who provided results on glacier mass changes.The following experts,who contributed ivdata and images for case studies shown the chapter:Iulii Didovets(Potsdam Institute for Climate Impact Research,Green Central Asia programme);Abror Gafurov(GFZ);Nikolay Kassatkin

31、(Central Asian Regional Glaciological Centre under the auspices of the United Nations Educational,Scientific and Cultural Organization(UNESCO);Kabutov Khusrav(Center for Glacier Research of the National Academy of Sciences of Tajikistan);Gulomjon Umirzakov(National University of Uzbekistan);and Rysk

32、ul Usubaliev(Central-Asian Institute for Applied Geosciences).WMO SECRETARIAT LEAD AUTHORSSulagna Mishra(Scientific Officer)and Stefan Uhlenbrook(Director,Hydrology,Water and Cryosphere),who were also supported by hydrology colleagues within the Secretariat in producing and reviewing the report.INDE

33、PENDENT CONSULTANTSAnastasia Lobanova and Iulii Didovets,who carried out the scientific analysis of the raw data to produce the results for the chapters on River Discharge,Soil Moisture,Evapotranspiration,Reservoirs,Lakes,Snow Cover and Glaciers and High-impact Hydrological Events.They contributed s

34、ignificantly to writing of the report with support from the authors mentioned above.Nilay Dogulu,who reviewed the report and designed the infographics and interactive Web version of the report(ArcGIS StoryMap)that can be found here.wgmsJOINT RESEARCH CENTREAND MANY MOREvAET actual evapotranspiration

35、DJF DecemberJanuaryFebruaryEW4All Early Warnings for All initiativeGDP gross domestic productGHMS global hydrological modelling systemGRACE Gravity Recovery and Climate ExperimentGRanD Global Reservoir and DamGRDC Global Runoff Data CentreHydroSOS Global Hydrological Status and Outlook SystemIGRAC I

36、nternational Groundwater Resources Assessment CentreIOD Indian Ocean DipoleISMN International Soil Moisture NetworkJJA JuneJulyAugustMAM MarchAprilMayNMHS National Meteorological and Hydrological ServiceSDG Sustainable Development GoalSON SeptemberOctoberNovemberSWE snow water equivalentTWS terrestr

37、ial water storageWHOS WMO Hydrological Observing SystemList of abbreviationsHYDROLOGICAL CONDITIONS AND SIGNIFICANT EVENTS OF 2023 Large-scale processes and WMO State of the Global Climate 2023(WMO No.1347):Theyear 2023 was marked by unprecedented heat,becoming the hottest year on record at 1.45 C a

38、bove pre-industrial levels.The transition from La Nia to El Nio conditions,as well as the positive phase of the Indian Ocean Dipole(IOD)contributed to this extreme heat and diverse weather impacts ranging from heavy rains and floods to droughts.River discharge:Compared to the historical period,2023

39、was marked by mostly drier-than-normal to normal river discharge conditions.Similar to 2022 and 2021,over 50%of global catchment areas showed river discharge deviations from near-normal conditions,predominantly lower than normal,with fewer basins exhibiting above-and much-above-normal conditions.Riv

40、er discharge:Large territories of North,Central and South America suffered severe drought and reduced river discharge conditions in 2023.The Mississippi and Amazon basins saw record-low water levels.The east coast of Africa experienced above-and much-above-normal discharge.The Horn of Africa,which h

41、ad suffered five consecutive dry rainy seasons,was affected by flooding.In Asia and Oceania,large river basins the Ganges,Brahmaputra and Mekong experienced lower-than-normal conditions over almost their entire basin territories.The North Island of New Zealand and the Philippines exhibited much-abov

42、e-normal annual discharge conditions.In northern Europe,the entire territory of the United Kingdom and Ireland saw above-normal discharge,as did Finland and southern Sweden.Reservoirs:The inflows into reservoirs showed a pattern similar to that of global river discharge,with India,North,Central and

43、South America,and parts of Australia experiencing below-normal inflow conditions.The basin-wide reservoir storage varied significantly,reflecting the influence of water management,with much-above-normal levels in basins like the Amazon and Paran,where river discharge was much below normal in 2023.La

44、kes:Lake Coari in the Amazon faced below-normal water levels,leading to extreme water temperatures,and Lake Turkana,shared between Kenya and Ethiopia,had above-normal volumes,following much-above-normal river discharge conditions.Groundwater levels:In South Africa the majority of wells showed above-

45、normal groundwater levels,following above-average precipitation in recent years;the same was true in India,Ireland,Australia and Israel.Notable depletion in groundwater availability was observed in North America and Europe due to prolonged drought.In Chile and Jordan groundwater levels were also bel

46、ow normal,with the long-term declines due to over-abstraction rather than climatic factors.Soil moisture:Levels of soil moisture were predominantly below normal or much below normal across large territories globally,with North America,South America,North Africa and the Middle East particularly dry d

47、uring JuneAugust.In contrast,certain regions,including Alaska,north-eastern Canada,India and parts of the Russian Federation,experienced much-above-normal soil moisture levels.The northern and south-eastern coasts of Australia,along with New Zealands North Island,also had above-normal soil moisture

48、due to wetter conditions and flooding.Executive summaryvi Evapotranspiration:Central and South America,especially Brazil and Argentina,faced much-below-normal actual evapotranspiration(AET)in SeptemberOctoberNovember.Mexico also experienced below-normal AET throughout almost all of 2023,reflecting s

49、evere drought conditions.Snow water equivalent:Most catchments in the northern hemisphere(except those in the northern United States and the Lena catchment far the eastern Russian Federation)had below-to much-below-normal snow water equivalent(SWE)in March,indicating lower-than-normal snow availabil

50、ity and below-normal spring flood potential.Seasonal peak snow mass for 2023 was much above normal in North America and much below normal in Eurasia.Glaciers:In 2023,glaciers lost more than 600 gigatons(Gt)of water,the largest mass loss registered in the last five decades.Following 2022,2023 is the

51、second consecutive year in which all glaciated regions in the world reported ice loss.Observed summer mass loss over recent years indicates that glaciers in Europe,Scandinavia,the Caucasus,north-western Canada,western South Asia and New Zealand have passed“peak water”(the threshold of maximum runoff

52、 due to melting),while the southern Andes(dominated by the Patagonian region),Russian Arctic and Svalbard seem to still present increasing melt rates.Terrestrial water storage:Large parts of the continents experienced below-average terrestrial water storage(TWS)conditions in 2023.Notable exceptions

53、were sub-Saharan Africa,the Tibetan Plateau and subregions of India,Australia and northern South America.High-impact hydrological events:Africa was the most impacted by extreme hydrological events in terms of human lives lost:In Libya where two dams collapsed due to flooding,over 11 000 lives were l

54、ost and the event affected 22%of the population.The floods also affected the Horn of Africa,the Democratic Republic of the Congo,Rwanda,Mozambique and Malawi,leading to additional toll of over 1 600 deaths.The southern United States,Central America,Argentina,Uruguay,Peru and Brazil were affected by

55、widespread drought conditions,which led to a 3%loss in gross domestic product(GDP)in Argentina and the lowest levels ever observed in the Amazon River and Lake Titicaca.KEY IMPROVEMENTS IN THE 2023 REPORT Expanded scope:The 2023 report includes new chapters and three new hydrological variables(lake

56、volumes,reservoir volumes,snow water equivalent),as well as an extended chapter on glaciers;thus,it provides a more comprehensive view of the global watercycle.Observed data:The number of river discharge measurement stations increased from 273 in 14 countries to 713 in 33 countries,and the groundwat

57、er data collection expanded to 35 459 wells in 40 countries,compared to 8 246 wells in 10 countries in the previous year(Figure 1).However,despite improvements in observational data,Africa,South America and Asia remain underrepresented in hydrological data collection,highlighting the need for improv

58、ed monitoring and data sharing,particularly in the Global South.Modelled data:Ten global hydrological modelling systems(GHMSs)(see Table A3 in theAnnex)provided substantial input that strengthened the analysis of variables,especially river discharge,evapotranspiration,soil moisture,snow and ice cove

59、r,and terrestrial water storage.vii Model validation:Modelled river discharge values showed agreement with observed data in over 73%of validated basins,especially in Central and Northern Europe,New Zealand,Australia and selected river basins in India,Myanmar and South America.Still,discrepancies bet

60、ween modelled and observed anomalies were not eliminated.Increased observed data availability is important for validation to properly assess model reliability in different regions around the globe.Intermodel comparison showed agreement in 97%of basins.REPORT IMPLICATIONS AND FUTURE OUTLOOKBy incorpo

61、rating new elements,guided by observational data that is improved both in quality and quantity compared to previous editions and modelling outcomes from multiple sources,this report delivers a detailed overview of the state of global water resources for the year2023.Additional objectives for future

62、editions of the report are to enhance the accessibility and availability of observational data(through both better monitoring and improved data sharing),further integrate relevant variables into the report,and encourage country participation to better understand and report water cycle dynamics.Futur

63、e reports are anticipated to include even more observational data,supported by initiatives like WMOs Global Hydrological Status and Outlook System(HydroSOS),the WMO Hydrological Observing System(WHOS),and collaboration with global data centres such as the Global Runoff Data Centre(GRDC),Internationa

64、l Soil Moisture Network(ISMN),International Groundwater Resources Assessment Centre(IGRAC),GEMS/Water Data Centre and the International Data Centre on Hydrology of Lakes and Reservoirs(HYDROLARE).viiiixThe release of WMOs State of Global Water Resources Report for 2023 builds on the success of the l

65、ast two reports in this new annual series,which was introduced in response to global calls for an independent and consistent assessment of water resources to inform policy discussions.The reports have garnered significant attention and endorsement from WMO Member States and Territories,the internati

66、onal community,partners and the media.They provide a clear overview of the status of water resources in major basins,comparing current data to long-term averages across various variables that represent the water cycle(also known as the hydrological cycle).The 2023 edition of the report further expan

67、ds on its predecessors by including additional variables such as in situ soil moisture data and reservoir storage,an overview of cryosphere components along with a review of major hydrological disasters that occurred globally in 2023.The report also saw an exponential increase in contributions from

68、WMO Members(through Hydrological Advisors and assigned focal points)in terms of both in situ data and modelled data.The reports preparation also relied heavily on global hydrological and land surface modelling systems,as well as remotely sensed data,ensuring broader global coverage and addressing da

69、ta gaps.Although data sharing and engagement have increased,achieving a globally uniform report based solely on hydrological observations remains a challenge,necessitating further investments in monitoring and data sharing in line with the WMO Unified Data Policy,and promoted by the WMO Hydrological

70、 Observing System(WHOS).The report also highlights the potential of Earth-system-based observations for infilling gaps in observational time series,which can be of great benefit to WMO Members.In the future,WMO is committed to including additional variables such as water quality in the annual report

71、s as well as exploring local trends via regional reports.Future reports will directly benefit from WMOs Global Hydrological Status and Outlook System(HydroSOS)as it becomes fully operational.The 2023 report illustrates the practical value of an annual synthesis of global water resources,providing es

72、sential insights for large-scale decision-making and policy development.It also supports and forms a solid backbone to facilitate the United Nations Secretary-Generals vision of a comprehensive early warning system(the Early Warnings for All(EW4All)initiative)and contributes to the achievement of th

73、e Sustainable Development Goals(SDGs)related to water and climate.Appreciation is extended to the steering committee,lead authors,and all contributors,including WMO Member National Meteorological and Hydrological Services,global data centres and supporting organizations.Foreword(Prof.Celeste Saulo)S

74、ecretary-General1The State of Global Water Resources report series offers a comprehensive and consistent overview of water resources worldwide,portraying the state of hydrological variables over thecourse of a year.The report offers a systematic and standardized analysis of water resources at a glob

75、al scale,which responds to the main outcomes of the UN 2023 Water Conference,which called for an“Operational Global Water Information System to support water,climate and land management for socioeconomic resilience,ecological sustainability and social inclusion by 2030”.1The preparation of the 2023

76、report was made possible through continuous involvement from WMO Members,represented by National Meteorological and Hydrological Services(NMHSs),as well as other organizations,including data centres,the global hydrological modelling community and the Earth observation community.The 2023 report offer

77、s advances in methodology and data sources:new chapters and variables have been added,including variables covering lake level,reservoir volumes and snow water equivalent,to present aneven more comprehensive overview of the year 2023 water condition globally.The number of observed data points receive

78、d from WMO Members,the Global Runoff Data Centre(GRDC)and other partners for river discharge measurements increased significantly,rising from 273stations in 14countries in 2022 to 713stations in 33countries in 2023.Similarly,for groundwater,data for 35459wells from 40countries were collected in 2023

79、,compared to 8246wells in 10countries in 2022(Figure1).The Soil moisture chapter now includes observed data provided by Members of the International Soil Moisture Network(ISMN),which were used to validate modelled results.IntroductionFigure 1.Increase in the number of countries,stations with observe

80、d river discharge data(both quality-controlled and not),groundwater wells and variables available for reporting in the years 2021,2022 and 202372021202022542023Countries14202127320227132023River discharge stations20218 246202235 4592023Groundwater wells320217202292023VariablesIncreasing participatio

81、n in analyses for State of Global Water Resources reports2The global hydrological modelling and Earth observation communities have made substantial contributions to the chapters on evapotranspiration,soil moisture,snow and ice cover,terrestrial water storage,lake levels and reservoir volumes.In tota

82、l,16different modelling and Earth observation-based data products were used for the 2023 report.These contributions have strengthened the analyses,particularly in ungauged or data-sparse regions,and have extended the number of products used,thereby helping to reduce uncertainty in the findings.The 2

83、023 edition includes chapters on River discharge,Reservoirs,Lakes,Groundwater levels,Soil moisture,Evapotranspiration,Terrestrial water storage and Snow cover and glaciers,each offering global and/or regional insights.Snow cover and glaciers focuses on snow water equivalent and the state of major gl

84、aciers worldwide.The High-impact hydrological events chapter provides a global overview of significant hydrological events from 2023,while the final Synthesis presents the major findings on the overall state of global water resources for the year 2023.The information presented in the report serves a

85、s a valuable resource for policymakers and decision makers,as well as water and disaster risk reduction professionals,contributing to a better understanding of global freshwater status and trends.In future editions,the report will also provide a historical perspective on the state of global water re

86、sources,adding to the understanding of regional and global trends.The present report directly supports the United Nations 2030 Agenda(Sustainable Development Goals(SDGs),especially SDG6:Clean Water and Sanitation,as well as other water-related SDGs by providing critical data for sustainable water re

87、sources management,addressing water scarcity,overabundance and water quality issues.The report also supports SDG13:Climate Action,informing strategies to align water resources management with climate change mitigation,by improving understanding of climate-related impacts on water(hydrological)system

88、s.Furthermore,the reports focus on observed and modelled datasets stresses the importance of open data sharing,reinforcing SDG17:Partnership for the Goals,by building global partnerships and enhancing cooperation across national,regional and global scales.Improving data sharing and engagement from W

89、MO Members in future editions of the State of Global Water Resources report will advance our understanding of the implications of hydrological processes for water resources,benefiting policymakers and decision makers,water resource managers,water users and the general public,and providing better val

90、idation of modelling results for river basins around the globe.These reports are helping to create anextensive global dataset of hydrological variables,which includes observed and modelled data from a wide array of sources.Thus,this work enhances global data sharing efforts,aligning with the focus o

91、f the global Early Warnings for All(EW4All)initiative on improving data quality and access for water-related hazard monitoring and forecasting,and providing early warning systems for all by 2027.It also aligns with WMOs Global Hydrological Status and Outlook System(HydroSOS)which provides a framewor

92、k for producing standardized status and outlook indicators to explain the current status and seasonal and sub-seasonal forecasts of hydrological conditions.3THE BACKDROP:OVERVIEW OF CLIMATIC CONDITIONS IN 2023 The year 2023 was characterized by record-breaking temperatures,making it the hottest year

93、 on record,with the global mean temperature reaching 1.45C(0.12C)above pre-industrial levels.2 Concentrations of the primary greenhouse gases carbon dioxide(CO2),methane and nitrous oxide continued to rise throughout 2023,with CO2 concentrations reaching 419.3parts per million by the end of the year

94、.3 Also,the decadal average temperature(20142023)was 1.200.12C above the pre-industrial average,marking this period as the warmest decade on record,with unprecedented monthly temperatures for both oceans and the atmosphere.4Fueled by heat,the year 2023 saw unprecedented extreme events in many parts

95、of the world.5 Heatwaves hit Europe,North America and China,while Canada faced its most extreme wildfire season ever recorded,with over 14.9million hectares destroyed by fire.6 In Libya,intense rainfall led to the collapse of three dams,with over 4700people losing their lives and 8000people consider

96、ed missing.Climate change likely contributed to increasing theevents rainfall intensity by up to50%,as well as to increasing the probability of the event.7Following three consecutive years of LaNia that concluded in early 2023,ElNio conditions started to emerge in the tropical Pacific Ocean during t

97、he boreal summer.However,the atmospheric response lagged,and it was not until early September that ElNio conditions were fully established in both the ocean and the atmosphere.8 This shift to ElNio resulted in varied weather impacts,including heavy rains,floods,droughts and heatwaves.The Indian Ocea

98、n Dipole(IOD)showed its first positive phase since 2019,peaking in October,which exacerbated dry and warm conditions in Australia and caused significant flooding in the Horn of Africa.The North Atlantic Oscillation(NAO)experienced an unusual negative phase in June and July,contributing to snow and i

99、ce melt in southern Greenland,as well as record-high temperatures across eastern Canada and Europe(Ireland,Belgium and Italy,among others).As shown in Figure 23 of State of the Global Climate 2023(WMO-No.1347),in 2023,total precipitation exceeded the normal level in several regions,with hotspots in

100、Asia and various parts of Africa,Europe and North America.Significant rainfall deficits were observed in Central and South America,Canada,the Mediterranean region,North Africa and others.Preliminary data for September2022August2023 show a significant loss in glacier mass that would be the highest on

101、 record(19502023),with an average balance of 1.2m of water equivalent.This severe loss is mainly due to extreme melting in western North America and the European Alps,where Switzerlands glaciers have lost about 10%of their remaining volume over the past two years.Snow cover in the northern hemispher

102、e has been decreasing in late spring and summer:in May2023,the snow cover extent was the eighth lowest on record(19672023).For North America the May snow cover was the lowest in the same period.4DATA SOURCESThe data used in the report were gathered from various sources(refer to Box1 and Data sources

103、 in the Annex),including NMHSs,the Earth observation community(which provided satellite-based observations)and the global modelling community,ensuring a robust,spatially consistent and comprehensive analysis.The River discharge and Soil moisture chapters are based on modelled and observed data.Where

104、 possible,in situ data were used to validate the modelled results.Global hydrological modelling systems(GHMSs)contributed to obtaining values for additional hydrological variables,in particular soil moisture,reservoir inflows,actual evapotranspiration and terrestrial water storage.The Groundwater le

105、vels chapter is based solely on observed data.Box 1DATA SOURCES 20239 Observed river discharge data:National Meteorological and Hydrological Services(NMHSs),the Global Runoff Database Centre(GRDC),10 enhanced streamflow observations using Earth-system-based products.11 Simulated river discharge data

106、:Ten global hydrological modelling systems(GHMSs).Inflow into selected reservoirs globally:Three GHMSs.Reservoir volume anomalies:United States National Aeronautics and Space Administration(NASA).12 Lake volumes:Global Water Monitor.13,14 Groundwater data:International Groundwater Resources Assessme

107、nt Centre(IGRAC)for 40 selected countries.Soil moisture:Three GHMSs.Observed soil moisture:Observed data from the International Soil Moisture Network(ISMN).Evapotranspiration:Five GHMSs.Terrestrial water storage(TWS):Gravity Recovery and Climate Experiment and thefollow-on satellites(GRACE/GRACE-FO)

108、,15 two GHMSs,ParFlow/CLM model for Central Europe.16 Glaciers:WMO Member States and Territories,World Glacier Monitoring Service(WGMS),Central-Asian Institute for Applied Geosciences(CAIAG),German Research Centre for Geosciences(GFZ),National University of Uzbekistan,Center for Glacier Research of

109、theNational Academy of Sciences of Tajikistan and external experts.Snow water equivalent:Environment and Climate Change Canada(ECCC).17,18 High-impact events:Contributions of WMO Members to WMO State of the Global Climate Report,open data sources such as the EM-DAT database,19 ReliefWeb and others.5

110、ANOMALY CALCULATIONFor each of the variables presented in the chapters,the anomaly20 was calculated by comparing the state in the year 2023 to the annual long-term means obtained from the historical period21(observed and historical,respectively),as described in Box2.Further details of the methods(in

111、cluding an overview of all data sources),the GHMSs used in the analysis,the definitions of the indicators used in the report,and additional results are documented in the Annex.Box 2The annual mean of each hydrological variable(for example,river discharge,inflow into reservoirs)for a defined referenc

112、e period of data(modelled or observed)was calculated for each year.Theranking of each respective variable in 2023 falls under categories based on the following definition:much below normal:Q2023 10th percentile below normal:10th Q2023 25th percentile normal:22 25th Q2023 75th percentile above normal

113、:75th Q2023 69%of basins)between observed and simulated anomalies(based on multi-model mean)for the year 2023,particularly in Central and Northern Europe,New Zealand,Australia,the upper part of the Paran River in Brazil and Paraguay,the Ganges in India and the Irrawaddy River in Myanmar.At the same

114、time,modelled anomalies disagreed with observations in South Africa,the upper Amazon Figure 3.Mean river discharge for the year 2023 compared to the period 19912020(for basins larger than 10000 km2).Theresults presented here are derived from the modelled river discharge data obtained from an ensembl

115、e of 10GHMS simulations(seeMethods in the Annex).Inset(bottom left)shows the percentage distribution of the modelled catchment area under the given conditions.Dark gray areas indicate no modelling data.The results were validated against hydrological observations wherever available(see FigureA6 in th

116、e Annex).World river discharge conditions in 2023NormalAbove and much aboveNo dataBelow andmuch belowmuch belowbelownormalmuch aboveabove7%45%31%17%8basin,the Lule basin(Sweden),the Nelson and upper Mississippi basins in North America,and theNiger River in Africa(for full validation results refer to

117、 FigureA6 in theAnnex).The location of the gauges with observed river discharge data is critical for reliable model validation,as presented in the Annex,FigureA5;in some locations,such as the Amazon river basin,gauges used for validation were too far away from the modelled outlets,which can undermin

118、e thevalidation results.This underlines the importance of the availability and comparability of the observed data and the modelled data.With respect to the historical period,the year 2023 was characterized by mostly drier-than-normal to normal conditions(Figure4).Similarly to 2022 and 2021,in more t

119、han 50%of global catchment area river discharge exhibited deviations from normal conditions;it was predominantly lower than normal,with a smaller proportion of basins exhibiting above-and much-above-normal conditions.At the global scale,the river discharge conditions in 2021 and 2022 followed a simi

120、lar pattern,with more areas experiencing drier-than-usual conditions compared to areas with wetter-than-usual conditions.In 2022,more area globally was under normal conditions than in 2021.27 A comparison of the areas under different river discharge conditions for every year from 1991 to 2023 using

121、a constant historical normal(19912020)showed a rising trend in dry areas over time,with 2023 being the driest in the last 33years,followed by 2021 and 2015.The last five consecutive years showed some of the lowest percentages of area under normal conditions over the past 33years.In 2023,below-and mu

122、ch-below-normal conditions prevailed in the Americas:across North America,except for Alaska,2023 mean discharge was lower to much lower than normal.Figure 4.The distribution of the area under different river discharge conditions for the years 19912023 1991202341%40%42%43%46%46%47%37%47%47%48%51%49%4

123、7%49%48%45%39%46%40%47%50%37%37%34%40%19%26%17%15%14%19%19%19%17%23%27%30%29%31%30%30%21%22%28%23%28%26%23%26%34%27%24%21%30%27%37%33%45%31%27%27%23%20%15%13%13%16%18%23%23%20%25%26%20%24%20%19%20%22%22%26%22%20%17%33%34%35%33%28%37%29%29%46%45%45%47%47%46%abovenormalbelow9The2023 drought in the Mis

124、sissippi and Ohio tributary basins,along with reduced groundwater from three consecutive years of drought in the Missouri tributary basin,resulted in record low water levels in the Mississippi River.28 The Yukon river basin in North America experienced above-and much-above-normal discharge condition

125、s.Below-to much-below-normal conditions gripped almost the entire territory of Central America and South America.On 26October2023 water levels in the Amazon river basin at the port of Manaus reached their lowest recorded level since 1902(12.70m).29 The transition from LaNia(2022/2023)to ElNio(2023)a

126、ppears to have been a key climatic driver in this record-breaking dry and warm situation,combined with a widespread anomalous warming over the worldwide ocean.30The east coast of Africa was characterized by above-and much-above-normal discharge as in the Limpopo and Zambezi river basins,and coastal

127、catchments in Tanzania,Mozambique and the Horn of Africa.The Horn of Africa,which had suffered five consecutive dry rainy seasons,was affected by flooding,triggered by ElNio conditions.31 In Libya the annual discharge conditions were indicated as above normal.The Niger,Lake Chad,Nile and Congo basin

128、s were characterized by below-normal discharge conditions.In Europe,the basins of the Danube and Dnieper were characterized by above-normal conditions.Additionally,central and western Europe saw normal discharge conditions,and in Italy river discharge remained normal.In Northern Europe,the entire te

129、rritory of the United Kingdom and Ireland saw above-normal discharge,as did southern Sweden,Norway and Finland.In the Russian Federation,the basins in the European part of the country and in Siberia(the Volga,Ob,and Northern Dvina)were characterized by lower-than-normal conditions,while a number of

130、river basins in eastern Siberia and the far eastern part of the country(such as the Lena and Ussuri)and the Kamchatka Peninsulas rivers saw above-and much-above-normal discharge conditions.Across the Middle East and Central Asia,discharge conditions remained lower than normal.In Asia and Oceania,lar

131、ge river basins such as those of the Ganges,Brahmaputra and Mekong experienced lower-than-normal conditions over almost the entire basin territories.In Australia,basins on the northern coast saw above-normal discharge conditions,while the MurrayDarling basin had predominantly normal conditions.The N

132、orth Island of New Zealand and the Philippines exhibited much-above-normal annual discharge conditions.10This chapter presents the state of the reservoirs in 2023 based on data from two sources:modelled inflow into selected reservoirs globally and anomalies in reservoir volume in 2023,obtained from

133、NASA,as a combination of satellite-based products,described in Biswas et al.32 INFLOW INTO SELECTED RESERVOIRSThe inflow data were obtained from three sources that comprise satellite-based(Global Water Watch)and GHMSs products,namely,the Wflow_sbm,33 CaMa-Flood with Dam34,35 and World-Wide HYPE(WWH)

134、models36(more details listed in TableA3 in the Annex).All available reservoirs from the above sources were included for analysis and were identified by their GRanDID.37 Daily inflow data into the selected GRanD reservoirs were computed from the three GHMS models for the historical period between 199

135、1 and 2020 and for the year 2023.Inflow anomalies were then calculated following the same method as for river discharge(seeBox2).Results are presented in Figure5.Water inflow into the reservoirs was selected as an indicator due to its low dependency on water resources management strategies such as r

136、eservoir operations.Inflow into reservoirs in 2023 generally reflected the overall discharge conditions,with the global balance being mostly below normal or normal.Specifically,reservoirs in India,particularly along the west coast,experienced below-and much-below-normal inflows.Similar conditions we

137、re observed on the east coast and the South Island of New Zealand.InAustralia,the MurrayDarling River also recorded below-normal inflows.In North and South America,reduced water availability was evident with lower-than-usual inflows into reservoirs,particularly in the Mackenzie River in North Americ

138、a,across the entire territory of Mexico,and in the Paran River in southern Brazil and Argentina.Across the Middle East and Central Asia,inflows into reservoirs remained lower than usual.ReservoirsFigure 5.Mean annual inflow into selected reservoirs in 2023 as compared to the historical period 199120

139、20.The size of the dots corresponds to the maximum storage volume of the reservoirs.The inset(bottom left)shows the percentages of reservoirs under the given conditions.normalbelowmuch belowabovemuch aboveMax.volume,km351030World reservoir conditions in 2023NormalAbove and much aboveBelow andmuch be

140、low17%40%43%11In contrast,South African reservoirs saw higher-than-usual inflows following wetter-than-usual discharge conditions.Northern Europe,particularly Sweden and southern Norway,also experienced increased reservoir inflows.However,in the far north of Norway,inflows were below normal.RESERVOI

141、R STORAGEThis section presents the results on basin-wide reservoir storage anomalies in 2023.Theapproach used involves merging several satellite-based datasets,as described in Biswas etal.38 Monthly individual reservoir storage time series were calculated and then accumulated into monthly basin-wide

142、 reservoir storage time series for 237basins(Figure6).Reservoir storage is influenced not only by climatic conditions and inflow into reservoirs but also by anthropogenic regulation of the storage.The effects of management can lead to results that differ compared to the inflow;for instance,inflow ca

143、n be low,but water can be stored,resulting in increased volume and decreased discharge downstream of the reservoirs.In Africa,the Orange,Zambezi,Congo,and Nile river basins exhibited much-above-normal reservoir storage levels.In Europe,the Danube and Rhine basins and the Iberian Peninsula experience

144、d much-below-normal reservoir storage.In contrast,Eastern European catchments such as the Dniepr in Ukraine saw much-above-normal storage,as did the Volga,Enisey and Ob river basins.In North America,the Nelson River and upper parts of the Mississippi River had much-above-normal basin-wide storage.Ho

145、wever,catchments in the eastern and southern United States and Mexico experienced much-below-to below-normal reservoir storage.In South America,reservoirs in the Amazon and Paran basins had much-above-normal storage levels.In Asia,the Ganges Basin in India and the Yangtze Basin in China saw above-no

146、rmal reservoir storage.InAustralia,the MurrayDarling Basin experienced much-above-normal reservoir storage levels.Figure 6.The annual mean of monthly basin-wide reservoir storage in 2023 with respect to the reference period(20002023)normalbelow normalmuch below normalabove normalmuch above normal12T

147、he water levels in 30 selected large lakes were obtained from the GloLakes product.39 TheGloLakes product estimates lake and reservoir storage data by combining measurements of water levels and water body extents from various satellites,with additional local topography information when needed.40,41

148、The data record starts in 1984 and is regularly updated as part of the Global Water Monitor and associated annual summary report.To determine the dynamics of lake and reservoir surface water extents,high-resolution optical remote sensing data from Landsat and Sentinel-2 satellites were used.The anom

149、aly was calculated with respect to the 19912020 historical period,and the 2023 annual volume anomaly is presented in Figure7.In the Amazon,the volume of Lake Coari was below normal.Record-breaking heatwaves and reduced water levels caused the water temperature rise to 34C,leading to an algae bloom a

150、nd causing the death of a substantial number of pink dolphins(Inia geoffrensis).42,43 The volume of Lake Superior,the largest lake in North America,was above normal in 2023;this began in December2022.44 Despite the drought event that affected Central America,Lake Nicaragua saw above-normal water vol

151、umes in 2023.Similarly,Lake Balaton in Central Europe experienced much-above-normal volume levels,as did Lake Peipus in Estonia and Lake Mlaren in Sweden.In Asia,the Small Aral Sea and Lake Aydar in Kazakhstan and Uzbekistan,as well as Eling Lake,Kaoyu Lake and Bositeng Lake in China,saw normal volu

152、mes in 2023.Hulun Lake and Lake Khsanka,which is shared by China and Russia,also experienced above-normal water volumes.Tonle Sap Lake in Cambodia,located in the Mekong river basin,exhibited above-normal water volumes as well.Lake Turkana,the worlds largest desert lake,which is shared between Kenya

153、and Ethiopia,had above-normal water volumes,following much-above-normal discharge conditions.Lakes Figure 7.Volume of 30 large lakes in 2023 as ranked with respect to the historical period 19912020 based on the GloLakes product 25 000450 000Capacity,109 litersTurkanaZhari Namco199120202023900 000230

154、000220000210000GL1 2 3 4 5 6 7 8 9 10 11 12Month1 2 3 4 5 6 7 8 9 10 11 12Month230000220000210000GLMonthly capacity,109 litersmuch belowbelownormalabovemuch above13This section provides an evaluation of groundwater levels in 2023 in comparison with historical records.45 It relies on in situ groundwa

155、ter level monitoring data made available by the national(subnational,in some cases)institutions in charge of groundwater monitoring.Intotal,groundwater level monitoring data were collected for over 160000wells in 40countries.Data were collected over the period covering the last 20years,from 2004 to

156、2023.Where it was not possible to collect the data over this entire period,for instance in countries where groundwater monitoring is less than 20years old,data covering the last 10years were used instead.This is the case for Brazil,Bulgaria,Costa Rica and Israel.Groundwater level monitoring data wer

157、e first filtered to guarantee a certain level of data consistency and completeness.After filtering,data could be analysed for some 35459 of the wells.46 In total,the average groundwater level in 2023 was much below normal in 6756wells(19%),below normal in 4087wells(11%),normal in 14030wells(40%),abo

158、ve normal in 3489wells(10%)and much above normal in 7097wells(20%).The results are shown on a world map and on a selection of regional maps(Figure8a and8b).Theresults show that the ranking is rarely uniform over a given area,because of the heterogeneous nature of aquifers and the importance of local

159、 variables influencing groundwater levels,such as a pumping well or the vicinity of a river.Nevertheless,regional patterns are observed,indicating that groundwater is also subject to regional influences.The average groundwater level in 2023 was below normal or much below normal in a high proportion

160、of wells over a large part of North America,in particular in the western and midwestern United States,and in central and northern Chile,western and southern Brazil,Southern Europe(Portugal,Spain,most of France),Central Europe(Hungary,Austria,Bavaria(Germany),the north of Poland),as well as in wester

161、n and southern Australia.Conversely,the average groundwater level in 2023 was above normal or much above normal in a high proportion of wells in New England(United States),the Maritime provinces of Groundwater levelsFigure 8a.Mean groundwater levels in 2023 as compared to the historical period of 20

162、042023(20142023 in the case of Brazil,Bulgaria,Costa Rica and Israel).Note:There are 3 175 monitoring sites comprising two or more monitoring stations.The results of these stations have been slightly displaced in the map to keep them from overlapping.BulgariaSouth AfricaCubaJordanIndiaRepublic of Ko

163、reamuch above normal above normal normalbelow normal much below normalAverage groundwater level in 202314Figure 8b.Snapshots for selected countries showing mean groundwater levels in 2023 as compared to the historical period (as in Figure 8a)010S20S30SLatitude80W 70W 60W 50W 40WLongitudeBrazil and C

164、hileCentral America and the Caribbean85W 80W 75W 70W 65W20N15N10NLongitudeLatitude10W 0 10E 20E 30E70N60N50N40NLongitudeLatitudeEuropeOceania120E 135E 150E 165E 15S30S45SLongitudeLatitudeIndia and Thailand30N20N10NLatitude70E 80E 90E 100ELongitudeNorth America60N45N30NLatitude120W 105W 90W 75W 60WLo

165、ngitude15Canada,along the Atlantic coast of north-eastern Brazil,Northern Europe(the British Isles and Scandinavia),Israel,Southern Africa,several parts of India,the Republic of Korea,eastern Australia,and the North Island of New Zealand.It is not straightforward to identify the reasons behind these

166、 regional trends,because groundwater is under the influence of climatic variables and other anthropogenic variables,such as abstraction and land use.Some aquifers have a rapid response time between the change in the boundary conditions(such as a groundwater recharge)and the corresponding change in g

167、roundwater level,47 however the response time in other aquifers can be several years or decades long.Nevertheless,some explanations can be put forward.In South Africa,the high proportion of wells where the average groundwater level in 2023 was above normal is consistent with the above-normal amount

168、of rainfall received in 2023 and the years before,48 while some of the wells with groundwater levels below normal can be linked to over-abstraction for irrigation.The impact of high precipitation in recent years on groundwater levels has also been observed in some parts of India,49 in Ireland,50 in

169、Australia51,52 and in Israel,for example.High precipitation directly contributes to an increase in groundwater levels through the recharge of aquifers.In countries where groundwater abstraction is significant,such as Australia,high precipitation also tends to reduce groundwater abstraction,as more s

170、urface water is available and the soil moisture is higher,which indirectly contributes to an increase in groundwater levels.The high proportion of wells where the average groundwater level in 2023 was below normal in Chile and in Jordan cannot be explained by climatic factors,reflecting instead the

171、long-term decline of groundwater levels due to over-abstraction.53,54 Theresults from India are mixed,however they rely predominantly on data collected in shallow dug wells(80%of total),55 where groundwater levels reflect the impact of the climate.It would be necessary to distinguish the monitoring

172、data collected in boreholes to assess the impact of over-abstraction due to groundwater irrigation,which is particularly significant inthe north-west of the country.56,57,58 Finally,the high proportion of wells where the average groundwater level in 2023 was below normal could reflect a combination

173、of climatic drought and over-abstraction.North America,for instance,was affected by the 20202023 North American drought,but is also subject to groundwater depletion,in particular in California and in the High Plains.59 Europe has also been affected by droughts in recent years,but there are cases of

174、groundwater over-abstraction,mostly in the southern part of the continent,for example in France,Hungary and Spain.60Despite the significant number of countries covered in this evaluation,the data availability is such that large parts of the world are missing from this analysis,in particular in Afric

175、a and in Asia.This does not mean,however,that there are no data.There are several countries where groundwater level monitoring data have been collected for less than 10years(such as theGambia,Rwanda and Somalia).It will be possible to include these countries in the evaluation within a few years,whic

176、h is a promising prospect.There are also challenges inaccessing the latest data.Data from Croatia and Qatar could not be used because most of the data from 2023 were not yet available for sharing.16Surface soil moisture is one of the crucial variables for hydrological processes.It influences the exc

177、hange of water and energy fluxes at the land surface/atmosphere interface,impacts streamflow generation,is important for biogeochemical cycles and co-controls vegetation development.Understanding soil moisture patterns is essential for sustainable water resources management and for the assessment an

178、d understanding of food production.61,62 OBSERVED SOIL MOISTURE FROM THE INTERNATIONAL SOILMOISTURENETWORKFor the 2023 assessment,ISMN63 applied strict filtering,selecting about 160stations globally,each with a minimum of 15years of data and more than 50%data availability(monthly),to visualize soil

179、moisture in three categories:below normal,normal and above normal.Thereport focuses on soil moisture at two depths:near-surface(up to 10cm)and deeper(down to 0.5m).The analysis includes data from up to 154near-surface stations and 90deeper stations.Thesoil moisture observations do not account for ir

180、rigation and may be influenced by human activities.The data show variability in soil moisture across regions.In Europe,47%of near-surface stations reported below-normal or normal conditions,while the United States exhibited 81%normal or above-normal conditions,although significant regional differenc

181、es were noted(Figure 9).It is reported that July was a very diverse month in terms of soil water availability.While substantial parts of the United States were under dry conditions,simultaneously wet conditions were observed over other parts of the country(10%of the contiguous United States).64 Note

182、 that the surface soil moisture is very dynamic compared with deeper soil layers where soil water is more persistent.A similar spatial clustering of in situ data can be observed in thedata fromthedeeper stations(Figure10).Within these clusters the majority Soil moistureFigure 9.Soil moisture in July

183、 2023 compared with all Julys 20082022(15-year reference period)for the top layer of soil(down to 0.11m).Theleft panel shows the situation in the contiguous United States,whereas south-west Europe is shown on the right.Due to limited data availability(data were available from 150stations 135 in the

184、contiguous United States and 15 in Europe all of which are displayed in the maps above),only limited data coverage is achieved by using in situ soil moisture data.120W 110W 100W 90W 80W45N40N35N30NLongitudeLatitude43.5N42.0N40.5N39.0N37.5N36.0NLatitude8W 6W 4W 2W 0 2E 4ELongitudebelow normalnormalab

185、ove normal120W 110W 100W 90W 80W45N40N35N30NLongitudeLatitudebelow normalnormalabove normalFigure 10.Soil moisture status down to 0.51m depth in September2023 in the contiguous United States.The reference data are the monthly averaged soil moisture of all Septembers 20082015.Due to limited data avai

186、lability,data from only 88stations located inthe United States could be analysed.17of soil moisture observation points reported above-normal conditions.Such conditions were reported for the western United States,while other parts of the country endured drought conditions.These findings highlight the

187、 need for long-term,widespread data to assess soil moisture conditions accurately at regional and global scales.MODELLED SOIL MOISTUREThe anomaly in surface soil moisture in 2023 has been obtained from three GHMSs(see TableA1 in the Annex for model names)and ranked relative to the historical period

188、19912020 on a monthly basis to understand root zone soil moisture patterns(2m depth).The anomaly calculation used was the same as for river discharge and reservoir inflow(as per Box1).The results are presented in Figure11.Figure 11.Soil moisture in 2023(Dec.2022Feb.2023 and Jun.Aug.2023)as ranked wi

189、th respect to the historical period 19912020.Greenland is masked in accordance with the Global Land Ice Measurements from Space(GLIMS).DecemberJuneJulyAugustJanuaryFebruarymuch belowbelownormalabovemuch above18Soil moisture in 2023 was predominantly below normal and much below normal across large te

190、rritories globally throughout the year.For example,almost the entire territories of North America,South America,North Africa and the Middle East experienced much-below-normal soil moisture levels,particularly during June,July and August.In fact,according to the United States Department of Agricultur

191、e(USDA),the proportion of the nations topsoil classified as dry or very dry peaked at 58%in mid-September.The year 2023 ranks just behind 2022 in therecent historical record for dry soils.65 Over the same period of JuneAugust,almost the entire territories of Europe,the Russian Federation,Central Asi

192、a and China experienced below-to much-below-normal soil moisture conditions.The same was observed in sub-Saharan Africa,including the Horn of Africa,which was actually affected by flooding.Only in South Africa,where 2023 was much wetter than usual,were soil moisture conditions above normal.Alaska,no

193、rth-eastern Canada,India and the north-eastern Russian Federation had much-above-normal soil moisture conditions.Similar conditions were observed along the northern and south-eastern coasts of Australia,as well as on the North Island of New Zealand,which was affected by flooding.Due to a mismatch in

194、 spatial representativeness and variation in the depth of the measurements between the modelled soil moisture data and the data from ISMN stations,the validation of modelled results was not possible.This highlights the importance of ensuring that observations are accessible and applied with good spa

195、tial coverage.Additionally,there was a variation inthescale of spatial representativeness between the modelled and observed data:the observed soil moisture is only representative for a few cm3 whereas the models represent a few km3.19Actual evapotranspiration(AET),which is one of the key elements in

196、 the hydrological cycle,refers to the process by which water is evaporated,encompassing evaporation from the soil or vegetation surface(including interception evaporation)and transpiration from plants.66 Elements influencing the rate of evapotranspiration include the level of solar radiation,atmosph

197、eric vapour pressure,humidity,air temperature,wind,soil moisture content and vegetation type and cover.This process is responsible for a large part of the water loss from thesoil during acrops growth cycle and is critical for understanding the state of water resources.Therates of AET are controlled

198、by the amount of water that is available(which is dependent on theexisting hydrological conditions in the basin)in addition to the meteorological forcing.This chapter presents an anomaly of AET at the global scale for four seasons in 2023 with respect to the historical period 19912020,derived from f

199、ive GHMSs(listed in the Annex,TableA1)and averaged over the river basins derived from the Hydrobasins level4 delineation.67 The seasons considered are:DecemberJanuaryFebruary(DJF)(includes December 2022),JuneJulyAugust(JJA),MarchAprilMay(MAM)and SeptemberOctoberNovember(SON).As presented in Figure12

200、,during the DJF and JJA months,AET rates were normal to below normal in sub-Saharan Africa,except for West Africa,the Niger and Lake Chad catchments,and the coastal basins in South Africa.In the Horn of Africa,the situation changed in the MAM and SON months,showing above-normal AET.In October,intens

201、e rainfall and associated flooding impacted the region.Territories in Libya,which were struck by Cyclone Daniel inSeptember,exhibited much-above-normal AET over the SON period.In India,the entire territory experienced much-above-normal AET during MAM,as did the Arabian Peninsula and parts of the Vol

202、ga and Don catchments in Eastern Europe.IntheRussian EvapotranspirationFigure 12.Seasonal actual evapotranspiration(AET)in 2023 as ranked with respect to the historical period 19912020 based on anensemble of five GHMSs June-July-AugustSeptemberOctoberNovemberMarchAprilMayJuneJulyAugustDecemberJanuar

203、yFebruary much belowbelownormalabovemuch above120W60W60E120E0120W60W60E120E020Federations far eastern catchments,such as the Ob and Enisey,AET was much above normal in both JJA and SON.Central Asian catchments,such as the Syr Darya,also saw much-above-normal AET during SON.In Central and South Ameri

204、ca,which were severely impacted by heatwaves and drought in2023,Brazil and Argentina experienced much-below-normal AET over large areas during SON.Mexico saw much-below-normal AET in DJF,JJA and SON.In the central part of theUnited States,AET was below normal or normal throughout the year,while nort

205、hern catchments like the Mackenzie had above-normal AET in MAM,JJA and SON.New Zealand had much above-normal AET throughout the entire year.Australian catchments were normal to below normal in AET during SON,mostly normal in MAM,and above normal in the northern territories during DJF and JJA.In Euro

206、pe,the Iberian Peninsulas catchments saw much-below-normal AET during MAM.Over SON,the entire territory of Central,Eastern and Northern Europe exhibited above-and much-above-normal AET.21Satellite gravimetry is a remote-sensing-based method(used by GRACE and GRACE-FO satellites)68,69 that is capable

207、 of observing all large-scale mass changes on and below theEarths surface.This includes,in particular,those caused by water storage changes,including insurface water,soil moisture,groundwater,as well as snow and ice.Terrestrial water storage(TWS),defined as the sum of all these storage compartments,

208、is expressed as an anomaly relative to its long-term mean in equivalent water heights in centimetres as an area-averaged height of the water column over the area being considered.This chapter provides results of the TWS anomaly in the year 2023 obtained from the GRACE/GRACE-FO-based product.The sect

209、ion on Terrestrial water storage in the Annex provides more details on TWS and how TWS anomalies were calculated.Figure 13 provides the TWS anomalies for 2023 in comparison to the 20022020 historical period,that is,the same reference period as for the State of Global Water Resources 2022(WMO-No.1333

210、).The TWS observations for 2023 reflect anomalies presented in previous chapters for other variables and further emphasize several critical hotspots for the year 2023.It should be noted that the integrative TWS signal shown here,also represents water storage variations in the unsaturated zone deeper

211、 than the soil moisture data shown in a previous chapter,besides groundwater.In particular,large territories around the globe saw below-and much-below-normal TWS values in 2023:Canada,Mexico and the southern United States as well as large parts of Southern,Central and Eastern Europe.Also,Northern Eu

212、rope saw some hotspots of much-below-normal TWS conditions in Sweden and Norway.In Africa,the entire area of sub-Saharan Africa exhibited much-above-normal TWS in 2023,as did the Horn of Africa.These positive TWS anomalies reflect the strong overall and longer-term water storage increase in these ar

213、eas after 2019 in particular,that is,a signal with longer persistence or memory effects,while below-average soil moisture conditions Terrestrial water storageFigure 13.Terrestrial water storage in the year 2023 ranked with respect to the historical period 20022020,that is,the same reference period a

214、s for the State of Global Water Resources 2022(WMO-No.1333).Note that Greenland and Antarctica are not included,as their ice mass balance trends are large and therefore hide the other TWS anomalies when plotted with the same colour range.much belowbelownormalabovemuch above22inparts oftheregion in 2

215、023(see Soil moisture chapter)represent the short-term near-surface dynamics.At the same time,TWS in Libya and Algeria remained much below normal in 2023.The entire territory of the Middle East,Central Asia and northern India saw much-below-normal TWS.On the other hand,in India,the upper Godavari ri

216、ver basin and basins in the central and western part of the country experienced much-above-normal TWS anomalies in 2023.In South America,dry conditions,with below-normal TWS,were experienced in the LaPlata region,with observations similar to those for soil moisture(see Soil moisture chapter).Much-be

217、low-normal TWS was also visible in South America along the Andes range,in particular in Patagonia,caused by ice-mass loss.In Australia,TWS was above normal to much above normal in the MurrayDarling catchment.The North Island of New Zealand saw normal TWS,while the South Island,on the contrary,saw mu

218、ch-below-normal TWS.CASE STUDY ON THE WATER STORAGE SITUATION IN CENTRAL EUROPE DURING 2023Figure 14 shows the simulated yearly anomaly for 2023 with regard to 20112022 for subsurface water storage(shallow groundwater from the land surface down to 60m depth)and near-surface subsurface water storage(

219、which includes the root zone,from 0 to 2m depth).Note that contrary to TWS from satellite gravimetry discussed above,these water storage data do not represent storage anomalies in surface water bodies,snow cover and glaciers.Much-above-normal subsurface water storage is simulated in the Kingdom of t

220、heNetherlands and north-western Germany due to a positive precipitation anomaly,leading to floods at the end of the year in that region.Dry conditions prevailed in France,southern and eastern Germany,the Alps,northern Italy and around the Baltic Sea.This dry anomaly is a continuation from the 2022 d

221、rought and preceding drought years in the area.However,near-surface water Figure 14.Total subsurface water storage(060m)and near-surface subsurface water storage(02m)in Central Europe in the year 2023 ranked with respect to the historical period(20112022)5E10E15E05E10E15E056N54N52N50N48N46N56N54N52N

222、50N48N46NTotal subsurface water storageNear-surface subsurface water LongitudeLongitudeLatitude23storage modelling shows a weakening of negative anomalies in 2023,caused by above-normal rainfall during spring and autumn.This is indicative of memory effects and the persistence associated with such ne

223、gative groundwater anomalies.70All data have been computed with the uncalibrated,physics-based model ParFlow/CLM at aresolution of 0.6km.71 Modelling approaches like this allow for a spatially continuous analysis,eventually leading to a better planning and management of water resources.For example,t

224、his hydrological modelling approach is used in a quasi-operational forecasting system,which produces daily forecasts with a lead time of nine days(see the German Wasser-Monitor for plant available water,www.wasser-monitor.de)as well as an experimental Water Resources Bulletin(www.adapter-projekt.de/

225、bulletin)providing seasonal forecasts four times per year of the total subsurface water storage over the upcoming seven months.However,the simulation results also show the need for in situ observations of various components of the water cycle(soil moisture content,groundwater level,river discharge,e

226、tc.),for example for validation,data assimilation and model-data fusion,72 which is only possible through dense hydrological monitoring networks and open data sharing.24This chapter present the state of snow cover and glaciers in 2023,focusing on snow water equivalent in March,peak snow mass over th

227、e northern hemisphere and glacier mass balance.SNOW WATER EQUIVALENTThe March SWE in the northern hemisphere was obtained as an ensemble mean over the 19912023 period from four individual gridded products:(1)The European Space Agency Snow CCI SWE version2 product derived through acombination of sate

228、llite passive microwave brightness temperatures and climate station snow depth observations;73(2)The Modern-Era Retrospective Analysis for Research and Applications version2(MERRA-2)daily SWE fields;74(3)SWE output from the ERA5-Land analysis;75(4)The physical snowpack model Crocus76 driven by ERA5

229、meteorological forcing.March mean data from each product were regridded to a common 0.50.5 regular grid and averaged together(Figure15).This is the same suite of products currently used to produce annually updated SWE data for the Arctic Report Card77 and the Bulletin of the American Meteorological

230、Society(BAMS)State of the Climate Report.78 March2023 SWE values were converted to anomalies using the 19912020 reference period on a pixel-wise basis,as perBox1.In March,the SWE was much above normal in the northern catchments of the Lena and Khatanga Rivers in the far eastern Russian Federation.Th

231、e basins of the Dnieper,Don,Danube,Ural,Yangtze and Amur all experienced below-to much-below-normal March SWE levels likely due to earlier onset of snowmelt compared to the reference period as a result of increasing temperatures.In North America,March SWE in the Nelson catchment was above normal,and

232、 in the Columbia catchment,it was much above normal.The SWE in the Mackenzie and parts of Yukon catchments was normal.Snow cover and glaciersFigure 15.March 2023 snow water equivalent anomaly compared with the reference period(19912020).Results are based on four gridded products(see the Snow water e

233、quivalent section in the Annex for more details).much belowbelownormalabovemuch above25PEAK SNOW MASS IN NORTH AMERICAN BASINSDaily frequency SWE output from the Crocus-ERA5 snow model79 was aggregated over a given land region to produce daily snow mass time series.Peak snow mass values were then ca

234、lculated for each water year,and the resulting series of values were used to calculate 2023 percentiles relative to the 19912020 reference period(Figure16).In the majority of the North American basins the peak snow mass in 2023 was within the historical normal.Only in the Yukon,Nelson-Saskatchewan,C

235、hurchill and Colorado river basins and the Great Basin was the peak snow mass above or much above normal.Seasonal peak snow mass for 2023 was much above normal in North America and much below normal on the Eurasian continent.GLACIERSThe present assessment of global glacier mass loss is based on a co

236、mbination of glaciological field measurements(500glaciers or 1%of global glaciers)and geodetic satellite measurements(200000 glaciers or 96%of global glaciers)derived from the Fluctuations of Glaciers(FoG)database compiled by the World Glacier Monitoring Service.80,81 Winter and summer regional bala

237、nces are calculated by downscaling the annual values using seasonal observations from FoG and the sine function analytical model proposed by Zemp and Welty(Figure17).82 GLACIER CONTRIBUTION TO SEASONAL RIVER RUNOFFThe annual mass balance of a glacier,defined as the difference between winter snow acc

238、umulation(mass gain)and summer melt(mass loss),reflects atmospheric conditions and serves as a key indicator of climate change.The global net loss of glacier mass contributes to sea level rise.Seasonal melting of ice and snow contributes to runoff.Therefore,glaciersFigure 16.Box and whisker plot(lef

239、t)showing seasonal peak snow mass for 2023 compared to historical spread(19912020)over various regions:entire northern hemisphere(NH),Eurasian continent(EA),North American continent(NA)and selected North American basins(numbered).Box and whiskers illustrate historical spread with percentile values a

240、s shown in legend.Values for 2023 shown by red lines.Map(right)illustrates category rankings for 2023 snow mass compared to reference period.1234567891011121314 Arctic Seaboard North Arctic Seaboard South Mackenzie River Yukon River Alaska Seaboard North Alaska Seaboard South Fraser/Pacific North Co

241、lumbia River Great Basin Colorado River Atlantic Canada St.Lawrence River Nelson-Saskatchewan River Churchill River 1234567891011121314much belowbelownormalabovemuch aboveBasin-aggregate peak snow mass for 2023 and historical spread North American basinsQ202390th75th25th10th5004003002001000North Ame

242、rican Snow Mass(Gt)5 0004 0003 0002 0001 0000Hemispheric snow mass(Gt)NH EA NA 1 2 3 4 5 6 7 8 9 10 11 12 13 1426Figure 17.Annual and seasonal mass changes in gigatonnes(Gt)from 1976 to 2023 for the 19 GTN-G glacier regions.Annual net mass loss is represented in red and net mass gain in blue with wh

243、ite corresponding to balanced years.The colour scale is set to the regional annual net mass change range,with darker colours representing the most negative and positive years,respectively.83AlaskaWestern Canada and USAArctic Canada NorthArctic Canada SouthGreenlandIcelandSvalbard and Jan MayenScandi

244、naviaNorth AsiaRussian ArcticCentral EuropeCaucasus and Middle EastCentral AsiaSouth Asia WestSouth Asia EastTropicsSouthern AndesNew ZealandAntarctic and Subantarctic27contribute to seasonal runoff even in years with balanced conditions or positive annual mass balance.This can be seen in Figure17,w

245、here negative summer mass balance values(ice mass loss contributing to river flow)are measured even in years in which regions experienced anet positive annual mass balance(blue bars,for example the early 1990s in Scandinavia,or 1983 in most regions).In many regions,precipitation and snowmelt primari

246、ly drive seasonal streamflow,but glaciers play a crucial role during specific months,especially in arid and semi-arid regions.Here,thedelayed release of meltwater from glaciers helps sustain river flows during the driest months and periods of drought.84,85,86,87,88As glaciers respond to warming,thei

247、r runoff initially increases,reaching a point of“peak water”,89 after which it declines as glacier volumes shrink.90 If temperatures continue to increase,the glacier will disappear,and with it,its hydrological contribution.This trend is expected globally,with significant reductions in glacier runoff

248、 by the centurys end,particularly in Central Asia and the Andes,where glaciers provide over 50%of basin runoff.Many regions with smaller glaciers have likely already passed peak water.91THE YEAR 2023 IN CONTEXTIn 2023,glaciers lost more than 600Gt of water,the largest mass loss registered in the las

249、t five decades.This is about 100Gt more than in any other year on record since 1976,equivalent to 1.7mm of contribution to global mean sea level rise.After 2022,2023 is the second consecutive year in which all glaciated regions in the world reported ice loss.Global estimates of annual glacier mass l

250、oss are good indicators of annual glacier contribution to global sea level rise.However,because winters and summers occur at different times of the calendar year in the two hemispheres,looking at global winter and summer estimates is not as good a proxy to understand the impact of annual glacier mas

251、s loss on the hydrological cycle.Regional winter and summer mass balances,however,can provide a better understanding of the evolution and impact of glacier contribution to runoff.Glaciers in many regions were close to balanced or had slightly negative conditions during the 1970s and 1980s,with alter

252、nating years of positive and negative balances.Since the 1990s,ice loss has been increasing in almost all regions,and it accelerated considerably after 2000.92 This is mostly due to regions consistently presenting larger summer melt than winter accumulation after the 1990s(Figure18).In most regions

253、dominated by small glaciers,peak water has already been reached,or it is expected to occur within the coming decades.93 The slightly reduced summer balance trends observed in Central Europe,Scandinavia,the Caucasus and Middle East,Arctic Canada North,South Asia West and New Zealand over the last yea

254、rs might indicate that these regions have passed peak water conditions.In contrast,the Southern Andes(dominated by the Patagonian region)and Russian Arctic,as well as Svalbard and Jan Mayen,seem to present melt rates that are still increasing slightly(Figure17).In Central Asia,approximately 28000gla

255、ciers in the Tien Shan and Pamir mountains serve as vital sources of fresh water,providing essential meltwater for agricultural,domestic and industrial use in the densely populated lowlands.However,over the years,most glaciers in Central Asia have shown a negative trend in mass balance.Small glacier

256、s,in particular,exhibit more intensive retreat,evidenced by a significant reduction in area and surface elevation.28Figure 18.Glaciers and their mass balances as measured by glaciological expeditions conducted in Central Asia in 2023Source:Nikolay Kassatkin,Central Asian Regional Glaciological Centr

257、e under the auspices of UNESCO;Kabutov Khusrav,Center for Glacier Research of the National Academy of Sciences of Tajikistan;Abror Gafurov,GFZ;Gulomjon Umirzakov,National University of Uzbekistan;Ryskul Usubaliev,CAIAG,Iulii Didovets,Potsdam Institute for Climate Impact Research,Green Central Asia p

258、rogrammeGlacier No.139TuyuksuPakhtakorBarkrakAbramovBarkrakPakhtakorTuyuksuGlacier No.139BarkrakAbramov,Golubin,West Suek,354,599TuyuksuGolubin599354West SuekAbramovKyrgyzstanChinaKazakhstanSource:Nikolay Kassatkin,Central-Asian regional glaciological centre of category 2 under the auspices of UNESC

259、O;Kabutov Khusrav,Center for Research of Glaciers of the National Academy of Sciences of the Tajikistan;Abror Gafurov,GFZ German Research Centre for Geosciences;Gulomjon Umirzakov,National University of Uzbekistan;Ryskul Usubaliev-Central-Asian Institute for Applied Geosciences(CAIAG);Iulii Didovets

260、,Potsdam Institute for Climate Impact Research,Green Central Asia program Boundaries of the terminal part of the glacier tongueGeodetic mass balance Glaciogical mass balance14914192429mm w.e.0200400600800Barkrak Sredniy Barkrak Sredniy East branch2017 2018 2019 2020 2021 2022 20230500 1 0001 5002 00

261、0Abramov Golubin No.354 No.599 West Suek2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023mm w.e.29For instance,the Central Tuyuksu Glacier in Kazakhstan recorded a mass balance of 28.0m or 0.42m water equivalent per year from 1958 to 2022.In Uzbekistan during the 2022/2023 season the

262、Barkrak Glacier experienced its highest melt since surveys began in 2016,with a change of 81cm.Figure18 presents the mass balance data for the Barkrak and Tuyuksu glaciers,alongside photos from other glaciers in the region obtained during expeditions in 2023,highlighting these changes.Similarly,the

263、glaciers of tropical areas(low latitudes)in northern South America(specifically in Colombia)are also natural indicators of the climate change trend.The glacier area in Colombia continues to decrease,despite the occurrence of the LaNia climate variability phenomenon in 2021 and 2022.At the beginning

264、of 2022,it was 33.090.63km2,which,compared to the area at the beginning of 2021(34.200.67km2),shows a reduction of approximately 1.11km2(3.2%)of the national glacier cover.9430This chapter presents a non-exhaustive review of selected major extreme events that occurred in 2023(Figure 19).The events w

265、ere selected based on the number of deaths(100)or overall impact on people affected/displaced,using data from several sources,including the EM-DAT database,95 WMO State of the Global Climate 2023(WMO-No.1347),direct communication of WMO Members to the WMO Secretariat through an online form and other

266、 public sources such as ReliefWeb.FLOODING IN LIBYAThe extreme Mediterranean tropical cyclone Daniel reached north-eastern Libya on 10 and 11September,leading to unprecedented rainfall.Al-Bayda station recorded an extraordinary 414mm of rain within a 24-hour period,which caused severe flooding acros

267、s the area.Themost catastrophic effects were witnessed in Derna,where significant portions of the city centre were destroyed and swept into the sea due to floodwaters and the collapse of two dams.96 The disaster was unprecedented,leading to at least 4700 deaths,with more than 8000 missing.97 It affe

268、cted nearly 22%of the nations population.98 The estimated cost for reconstruction and recovery from the devastating floods amounts to USD 1.8billion,which represents 3.6%of Libyas gross domestic product(GDP)for 2022.99 The housing sector was particularly hard hit,with over 18500homes either destroye

269、d or damaged,accounting for 7%of all housing in the country.100FLOODING IN DEMOCRATIC REPUBLIC OF THE CONGO AND RWANDAFrom 2 to 5May2023,a significant flooding event accompanied by landslides impacted theLake Kivu area,situated on the border between Rwanda and the Democratic Republic of the Congo,in

270、 Central Africa.On 2May,Mushubati in Rwanda recorded 182.6mm of rainfall,setting a new national daily record.101 The event resulted in at least 574casualties,with 443in the Democratic Republic of the Congo and 131 in Rwanda.102FLOODING IN THE HORN OF AFRICAFollowing five consecutive seasons of below

271、-average rainfall,which led to one of the most severe droughts ever recorded in the region,the Horn of Africa experienced significant flooding in 2023,especially later in the year,due to heavy rains linked to ElNio and the positive Indian Ocean Dipole.103 Starting in October,this persistent rainfall

272、 caused almost 4million people to be displaced throughout Somalia,Kenya and Ethiopia.104 In these devastating events,more than 350persons lost their lives in Somalia,Kenya and Ethiopia.105 FLOODING IN MOZAMBIQUE AND MALAWIIn March 2023,Malawi and Mozambique faced one of the most severe tropical cycl

273、ones on record,Tropical Cyclone Freddy,which originated in the Western Indian Ocean and tracked eastwards.106 This storm brought unprecedented rainfall to southern Malawi.The most devastating effects of Freddy occurred during its final landfall,affecting both Mozambique and Malawi with exceptionally

274、 intense rainfall,reaching up to 672mm in Mozambique.107 High-impact hydrological events31Figure 19.Selected notable high-impact hydrological events across the globe in 2023DroughtFlood/Heavy rainfallData sources:WMO Members,State of the Global Climate 2023(WMO-No.1347),EM-DAT and othersOn 7 to 9 Au

275、gust,storm Hans caused extreme flooding and 700 landslides,damaging major train lines,roads and buildingsExtreme river flooding event at Sutlej River,August 2023:160 000 people afected,600 km2 inundatedTyphoon Doksuri(Egay):flooding led to 45 deaths in the Philippines and 56 in China,and more than U

276、SD 13.2 billion in lossesDrought in Central America,Mexico and the USA throughout 2023:21%below-average precipitation in MexicoDrought in Argentina led to 3%GDP loss,Rio Negro in Brazil recorded historic low in October 2023Flooding in Italy afected100 municipalities,12 000 people evacuatedFlood in L

277、ibya afected 22%of countrys population:4 700 deaths,8 000 missingOn 2 to 5 May 2023,a flooding event led to 443 deaths in the Democratic Republic of the Congo and 131 in RwandaTropical Cyclone Freddy:679 deaths in Malawi and 165 in Mozambique,and USD 680.4 million in losses in MalawiFlooding caused

278、by Cyclone Gabrielleresulted in between USD 5.3 billion and USD 8.6 billion in economic lossesAfter 5 seasons of drought,flooding hit the Horn of Africa in 2023,resulting in 352 deaths32Bothcountries were still reeling from storms in 2022.108,109 Malawi,in particular,was significantly affected by Fr

279、eddy,with at least 679lives lost,110 and Mozambique reported a further 165fatalities.111 The total cost of recovery and reconstruction is USD680.4million in Malawi.112 DROUGHT IN CENTRAL AMERICA AND THE SOUTHERN UNITED STATES Throughout 2023,a severe drought spread from the southern United States ac

280、ross much of Mexico and Central America.113 Initially emerging in Honduras and Panama in April,the drought extended to most of eastern Central America by May and reached much of Mexico by June and July.114 By late August,areas in eastern Texas and Louisiana(United States)were experiencing exceptiona

281、l drought conditions.Mexico recorded its driest year ever,with precipitation levels 21%below normal,impacting nearly all regions at various times throughout the year.However,late in the year,tropical cyclones brought significant rainfall that alleviated drought conditions in Baja California and some

282、 Pacific coastal areas.115 Also,in August2023,the negative precipitation anomaly showed slight improvement in eastern Central America,specifically Honduras,Nicaragua and Guatemala,yet meteorological drought conditions continued to persist across the region.116 Heatwave and associated drought caused

283、USD14.5billion losses in the United States.117DROUGHT IN ARGENTINA,URUGUAY AND BRAZILFrom August 2022 to March 2023 in Argentina,rainfall was 20%to 50%below normal across much of the northern and central regions,marking the fourth consecutive year of significantly reduced precipitation.118 Uruguay f

284、aced critically low water storage levels,affecting water supply in Montevideo and other large centres.119 In Brazil,the Amazon saw below-normal rainfall,with eight states experiencing the lowest rainfall from July to September in over 40years.120 On 26October the Rio Negro at Manaus saw the lowest l

285、evel recorded since 1902,with water levels reaching 12.70m.121 The Amazon region experienced a loss of storage between 2022 and 2023,resulting in the longest drought ever recorded in the basin.122,123 In the central and north-eastern regions of Brazil,the gain in groundwater storage can be associate

286、d with intense precipitation processes between 2022 and 2023,124,125 interrupting a long trend of storage loss.126 In a complementary way,in the south-eastern portion of Brazil a loss of storage was observed in the monitoring wells with a probable origin in the typical pattern of precipitation induc

287、ed by LaNia a dipole of anomalies between the north-east and the south-west.127 The drought led to a 3%GDP reduction in Argentina in 2023.128DROUGHT IN PERU During January 2023,several rivers on the Lake Titicaca drainage(TLD)in Peru presented hydrological droughts characterized as extreme by the Na

288、tional Meteorological and Hydrological Service of Peru(SENAMHI).Thus,the river discharges of the TLD tributaries to Lake Titicaca in Peru(Ramis,Coata,Huancan and Ilave)presented anomalies characterized by SENAMHI as“well below normal”;these droughts had been more extreme since the 1990s.129 These ri

289、vers discharge anomalies in the TLD are associated with the precipitation deficits that occurred during the pre-rainy-season period(OctoberDecember2022),when the TLD and the adjacent AndeanAmazon region experienced reductions of up to 60%in precipitation.Consequently,Lake Titicaca water levels decre

290、ased by 0.05m from December to January.Such conditions had not been seen since the ElNio-related drought of 1982/1983.Thisnew 33historic drought was associated with southern moisture flux anomalies,which reduced theinput of moisture-laden winds from the Amazon Basin to the TLD.Anomalies of this type

291、 inmoisture transport had not been observed since at least the 1950s.130FLOODING ON THE NORTH ISLAND OF NEW ZEALANDIn early 2023,the east coast of New Zealands North Island faced severe flooding during Cyclone Gabrielle on 1314February,which delivered over 500mm of rainfall in a day in some areas,re

292、sulting in 15deaths131 and economic losses estimated between USD5.3billion and 8.6billion.132,133 FLOODING IN CHINA AND THE PHILIPPINESIn July 2023 Typhoon Doksuri(Egay)caused substantial flooding in both the Philippines and China,with some of the most significant flooding occurring in the Beijing r

293、egion from the remnants of the storm.A 24-hour total of 744.8mm was observed at Wangjiayuan Reservoir,in the hills near Beijing.Doksuri led to 56fatalities in China,and 45 in the Philippines.134,135 Officials in China have estimated an economic loss of more than USD13.2billion.136FLOODING IN ITALY T

294、wo intense rainfall events in the first half of May(13May,1618May)led to extensive flooding in Italy.137 The hydrological combination of the two intense weather events,which had similar amounts of rainfall(210mm total precipitation in the first one,240mm in the second one),138 amplified the impacts

295、of the second one,resulting in the flooding of an area of 540km2 with approximately 350million cubic metres of water.139 This impacted 100municipalities in the Emilia-Romagna region.Twenty three rivers overflowed,due mainly to diffuse levee breaches,and 13others rose to alarming levels,resulting in

296、thousands of landslides,which led to 15persons losing their lives and 23067individuals being evacuated.140 The majority of evacuees were in the Ravenna area(16445),with 4462 in the province of Forl-Cesena and 2160 in the Bologna area.141 The flood caused USD8.69.75billion in losses.142,143 Early war

297、ning systems in Italy144,145STATE OF EMERGENCY AND ACTIONS TAKEN DURING THE EMILIA-ROMAGNA FLOODS,MAY 2023The national early warning service(network of regional coordinated centres)issued red alerts on 16May with 24hours notice and the description of the expected impacts,in particular,a forecast of

298、floods close to the embankment levels and historical maximums in the Romagna basins and tributaries of the Reno River,and the possibility of numerous and extensive landslides.The precipitation observed in the first half of May was eight times the climatological monthly average.146 Twenty three river

299、s had overflowed by 25May2023,and 13 had reached threatening water levels,resulting in thousands of landslides,15 deaths,the evacuation of more than 23 000 people and theclosure of almost 700 roads.147,148,149Role of the Early Warnings for All(EW4All)initiative:The advance prediction of the event,wi

300、th the issuing of the civil protection red alert,allowed the highest level of mobilization to be put in place,through the activation of the national Crisis Unit and the regional mobile columns,150 with numerous evacuations,both preventive and during the event.34SynthesisThis 2023 edition of the Stat

301、e of Global Water Resources report continues to build on the increasing engagement from WMO Members,NMHSs and global hydrological modelling communities.The 2023 report benefitted from a significant increase in observed data points.The number of in situ discharge measurement stations rose from 273 in

302、 14countries in the previous annual report to 713stations(out of 1595stations that were available in total,many of which could not be used because of gaps in the time series)in 33countries.There was also a substantial increase in groundwater data collection,with data from over 35000 wells in 40count

303、ries being used(out of more than 130 000 from which data were originally collected),compared to 8246wells in 10countries in 2022.This increased availability of data has been crucial for assessing water resource conditions more extensively and validating the modelling tools used.The majority of data

304、points for discharge were concentrated in Europe and North America,with 46%and 21%of the stations,respectively.Meanwhile,Africa,South America and Asia were still underrepresented,underscoring the need for increased and improved hydrological monitoring efforts and data sharing in underrepresented reg

305、ions,particularly in the developing countries.Also,stations in Europe were located mainly in Scandinavia,which could influence the interpretation of the results,as the signal from Southern/Central Europe will be missing from any analysis based on in situ observation only.The contribution from the In

306、ternational Soil Moisture Network(ISMN)underscores the importance of in situ soil moisture data.These soil moisture measurements are foundational for validating satellite and modelled soil moisture products and are crucial for environmental assessments.However,challenges persist with in situ data(ou

307、t of 3000stations in the ISMN network,only 160 could be used for this study due to data gaps),including their localized nature,lack of standardization across institutions and difficulties in maintaining data continuity when sensors are replaced.Despite these challenges,in situ data remain vital as t

308、he only direct measure of soil water availability.The 2023 report also highlighted the potential usage of Earth observation-based products to augment existing observation data by infilling gaps.In general,an urgent need remains for more support from WMO Members to build better monitoring networks an

309、d use innovative methods to improve data management and data sharing.The 2023 report includes new chapters and variables,such as lake volumes,reservoir volumes and snow water equivalent,thus offering a more comprehensive picture of the global water cycle.This expanded scope contributes to a better u

310、nderstanding of the interconnectedness of different hydrological factors and their impact on water resource management.Substantial contributions from the global hydrological modelling community strengthened the analysis of variables such as evapotranspiration,soil moisture,snow and ice cover and ter

311、restrial water storage(TWS).These contributions are particularly valuable for data-sparse regions and help reduce uncertainty in the findings,providing more reliable information for policymaking.Validation of modelled results for 2023 showed agreement in over 73%of basins between observed and simula

312、ted anomalies,especially in Central and Northern Europe,New Zealand,Australia,the upper Paran River in Brazil and Paraguay,the Ganges in India and the Irrawaddy River in Myanmar.However,discrepancies between modelled and observed anomalies were noted in South Africa,the upper Amazon basin,the Lule b

313、asin in Sweden,the Nelson and upper Mississippi basins in North America,and the Niger River in Africa.While models are able to provide a coherent and trustworthy picture of the discharge conditions in many catchments around the world,validation of the results plays a critical role in the assessment

314、of the results.In general,a global systematic observing system for the global hydrological cycle is still lacking,due to lack of in situ measurements and/or data exchange.This report highlights the benefit of having both better monitoring and the implementation of the WMO Unified Data Policy for hyd

315、rological observations to ensure that Members are able to calibrate and run hydrological models which help in assessing the current status as well as make 35forecasts,thus aiding water management.The principle of having a common method,used across the globe,for the indicator calculations and common

316、variables also underpins the WMO HydroSOS initiative to unite hydrological monitoring and forecasting systems worldwide.The year 2023 was marked by unprecedented heat,becoming the hottest year on record at 1.45C above pre-industrial levels.Europe,North America and China faced heatwaves,while Canada

317、experienced its most extreme wildfire season ever,with over 18million hectares affected.The transition from LaNia to ElNio conditions contributed to this extreme heat and varied weather impacts,including heavy rains,floods and droughts.Total precipitation in 2023 exceeded the long-term normal in sev

318、eral regions,including East and Central Asia,parts of North Asia,the western Indian summer monsoon area,and parts of Africa,Europe and North America.Significant rainfall deficits were observed in south-eastern South America,the Amazon basin,much of Central America,southern Canada,the western Mediter

319、ranean region,and parts of Africa and Asia.The year 2023,compared to the historical period,was marked by mostly drier-than-normal to normal discharge conditions.Similar to 2022 and 2021,over 50%of global catchment areas showed river discharge deviations from near-normal conditions,predominantly lowe

320、r than normal,with fewer basins exhibiting above-and much-above-normal conditions.In the Americas,below-and much-below-normal conditions prevailed across large territories.Throughout most of North America,except for Alaska,2023 was characterized by below-to much-below-normal discharge conditions.In

321、fact,in the southern United States drought conditions had already been in place for more than three years.In 2023 Central America and South America also experienced below-normal to much-below-normal conditions across almost their entire territories.In 2023,every country in the Amazon basin saw recor

322、d low levels of rainfall.As a result,reservoir inflows were lower than usual across North and South America,particularly in the Mackenzie River in North America,Mexico and the Paran River in southern Brazil and Argentina.Groundwater levels in North America were also below normal,particularly in the

323、western and central United States,as they were in central and northern Chile,and in western and southern Brazil,likely due to prolonged drought conditions.Also,soil moisture was below normal across North and South America during JuneAugust.As reported by the United States National Oceanic and Atmosp

324、heric Administration(NOAA),151 2023 ranks just behind 2022 in the recent historical record for dry soils in the United States.Following reduced water availability,the AET values were much below normal in Central America,Brazil and Argentina in SeptemberNovember,and over the entire year in Mexico.Muc

325、h-below-normal TWS values reflected significant water storage deficits in this region;for example,the La Plata region saw below-normal TWS,consistent with dry soil moisture conditions.North Americas Nelson and Columbia catchments saw above-and much-above-normal March SWE,respectively.Also,the peak s

326、now mass in the southern Colorado basin and Great Basin was much above normal.Glaciers in the southern Andes(dominated by the Patagonian region)presented slightly increasing melt rates.Discharge conditions in Europe saw varying patterns.Northern Europe,including the United Kingdom and Ireland,experi

327、enced above-normal river discharge,and groundwater levels were also above-normal.Reservoir inflows in Northern Europe,particularly Sweden,were higher than usual,reflecting the discharge patterns.Only the far north of Norway saw below-normal inflows.Central and Western Europe exhibited normal annual

328、discharge conditions;however,northern Italy was hit by a devastating flood.Much-above-normal subsurface water storage was observed in the Netherlands and north-western Germany due to positive precipitation anomalies,leading to year-end floods in those regions.Meanwhile,dry conditions persisted in Fr

329、ance,southern and eastern Germany,the Alps,northern Italy and the Baltic Sea area,continuing the drought trends from previous years,although near-surface water storage 36showed some improvement in 2023 due to above-normal spring and autumn rainfall.The TWS was below normal and much below normal acro

330、ss Southern,Central and Eastern Europe,with some hotspots in Sweden and Norway.The Iberian Peninsula faced much-below-normal AET during spring,while Central,Eastern and Northern Europe exhibited above-and much-above-normal AET over the autumn months.Groundwater levels were below normal in Southern E

331、urope,including Portugal,Spain and most of France,as well as Central Europe.Soil moisture conditions were predominantly below normal,particularly during June,July and August.March snow mass for 2023 was much below normal in the Eurasian continent,the basins of the Dnieper,Don,Danube,Ural,Amur and Ya

332、ngtze all experienced below-to much-below-normal March SWE levels.Groundwater levels in Southern Europe,including Portugal,Spain and most of France,as well as in Central Europe,were below normal.Glaciers of Europe and the Caucasus showed slightly reduced summer balance trends in 2023 as well as prev

333、ious years.Africa was hit by severe floods in 2023.Libya,Mozambique,Malawi,the Democratic Republic of the Congo,Rwanda and the Horn of Africa(which had suffered from five consecutive low rainy seasons)all faced severe flooding,likely triggered by ElNio conditions.The floods led in total to more than 12600casualties,with over 11000 victims in Libya alone.The east coast of Africa,including the Limpo