1. User Needs & Essential Water (Cycle) Variables (EWVs) (1) Water Strategy Report (WSR)—GEOSS-Water- CoP (2) GEO Societal Benefits Area (SGA)—Water-- Report Unninayar (NASA/GSFC-GESTAR)

2. User Needs and Essential Water Cycle Variables (EWVs) Developed by (1) GEO-UIC-SBA-Water (2010) & GEOSS Water Strategy Report CoP—(2015) Through review process with wide acceptance by the community EWVs are linked to applications and end-users. They are derived by reviewing/consolidating user- needs/requirements (for observations of water variables) in all GEO user sectors as defined by the GEO SBA’s Community agreement reached by review (process) and consensus EWVs are linked to international bodies (GEO and collaborating Member Organizations) Data base with information on EWVs: Various, as maintained by national, regional and international organizations and programs.

3. Broad User Categories Water Cycle Monitoring Water Cycle Modeling/Prediction Decision Support—Agriculture Decision Support--Climate Decision Support—Energy Decision Support—Ecosystems Decision Support—Biodiversity Decision Support—Health Decision Support--Land Management Decision Support—Oceans (Coastal) Decision Support—Water/Water Resources (Management) Decision Support—Weather

4. Broad User Categories 9 GEO SBA’s Agriculture Disasters Health Biodiversity Ecosystems Water Climate Energy Weather [ EWVs include/incorporate ECV’s (Essential Climate Variables—ECVs- -as per GCOS, UNFCCC, IPCC] [Each User Category was expanded into functional elements before requirements were consolidated. E.g., WRM includes stream flow forecasting, reservoir management, drought monitoring/forecasting…etc.]

5. Definitions: Essential Water Variables (EWV) are defined as water variables/parameters that address “user”-defined critical requirements for one or more of the following: (1) Observational “monitoring” of key elements of the global and regional/local water cycle, (2) Observations required by diagnostic and/or land surface/hydrological prediction models that are used to generate derived products for the end-user communities, and (3) Observational and model-derived variables and parameters required by users of water data/information products as applied to various inter-disciplinary decision support systems and tools. [Capture Key Elements of the Earth-Climate System—Figure-1]

6. Figure 1. The water cycle dominates the Earth-climate system, as shown in this schematic of the water cycle (USGCRP,2003).

7. EWVs PRIMARY Precipitation ET Snow Cover (& Depth, Freeze/Thaw Margins..) Soil Moisture/Temp Ground Water Run0ff/Streamflow/River Discharge Water Quality Water Use/Demand (Agro, Hydro, Energy, Urban,…) Glaciers/Ice Sheets

8. EWVs SUPPLEMENTARY VARIABLES Surface Meteorology Surface & Atmospheric Radiation Budget Cloud & Aerosols Land Cover & Vegetation, Land Use Permafrost Elevation/Topography and Geological Stratification [The above can be expanded into much more detailed sub- parameters/variables. E.g., Water Quality alone could have 10 to 100 or more constituents elements]

9. Essential Water Cycle Variables (EWC-V’s) [Structured following the Water-SBA analysis as being of approximately equal high priority when averaged across all user sectors. Some variables/parameters have been combined for simplicity] Water Cycle Monitoring Water Cycle Modelling/Prediction Decision Support:--Agriculture Decision Support--Biodiversity Decision Support--Climate Decision Support-- Ecosystems Decision Support--Energy Decision Support--Geohazards Decision Support--Health Decision Support--Land Management Decision Support—Oceans (Coastal) Decision Support--Socio-Economic Decision Support--Water Management Decision Support--Weather Cross-Ref.--ECV’s (Essential Climate Variables as per UNFCCC, IPCC) PRIMARY PrecipitationXXXXXXXXXXX XXX Evaporation & EvapotranspirationXXXXXX X Snow Cover (& Depth, Freeze Thaw Margins) XXX XXXXXX XXX Soil Moisture/TempXXXXXX X X X X GroundwaterXXX XX X X Runoff/Streamflow/River DischargeXXXXXXXXX X X X Lakes/ Reservoir Levels and Aquifer Volumetric Change XX XXX X X X Water QualityXX X X XXXXX Water Use/Demand (Agro, Hydro, Energy, Urban,...) XXX X XXXXX X Glaciers/ ice sheetsXX X X X X X SUPPLEMENTARY VARIABLES Surface MeteorologyXXX X X XX Surface & Atmospheric Radiation Budget XXX X X Cloud &AerosolsX X XX Land Cover &Vegetation + Land UseXXXXXX X XX X PermafrostXX X Elevation/ Topography & Geological Stratification XXX X X X

10. EWVs—Obs. Requirements Space/time resolution requirements (User Needs) vary substantially between user sectors From hours to days, week, month, season, year, decade, century,… Space/time resolutions also vary substantially with observing instrument/platform Data assimilation models are frequently needed to derive variables that are not measured directly, or measured with insufficient spatial/time density Requirements vary with early warning/prediction system and the “observable/variable” [ Detailed in the Water-SBA Report, and the WSR]