Assessing changes in water availability involves a range of topics and methodologies, including global circulation, observational data, regional studies, biogeochemistry, atmospheric processes, anthropogenic influences, and extreme events.
A major aspect of this Grand Challenge is the predicted shift from short term changes to long term changes in global circulation. To examine this shift, we will build on expertise from the WCRP Working Group on Coupled Modeling (WGCM), the WCRP Working Group on Seasonal to Interannual Prediction (WGSIP), and the Climate and Ocean – Variability, Predictability, and Change (CLIVAR) project and its programs. GEWEX is leading several activities that are linked to this issue, such as the Land Surface, Snow and Soil Moisture Model Intercomparison Projec (LS3MIP), the Land Use Model Intercomparison Project (LUMIP), and the High Resolution Model Intercomparison Project (HighResMIP) experiments within CMIP6.
Working on the problem of changing water availability requires access to long term global observations, which the GEWEX Data and Analysis Panel (GDAP) allows. These may include data from networks such as the Baseline Surface Radiation Network (BSRN) and the GCOS Reference Upper-Air Network (GRUAN).
The regional aspect of the Challenge, particularly modeling, will be tackled in conjunction with the Working Group on Regional Climate (WGRC) and the Coordinated Regional Climate Downscaling Experiment (CORDEX). Close collaboration between the GEWEX Hydroclimatology Panel and its Regional Hydroclimate Projects (RHPs) and Cosscut Projects (CCs) is central to its execution. In examining the cryospheric component, particularly high elevation mountainous regions, we will involve the Climate and Cryosphere (CliC) project and rely on GEWEX activities such as the International Network for Alpine Research Catchment Hydrology (INARCH) and MOUNTerrain. In the Himalayas, the Third Pole Environment (TPE) program will contribute to cold regions studies.
In examining the biogeochemistry portion of the Grand Challenge, we will liaise with sister projects from Future Earth, with the integrated Land Ecosystem-Atmosphere Processes Study (iLEAPS) playing a key role. Connecting to the water-energy-food nexus is a priority, and we will be collaborating with the Global Water Systems Project (GWSP) and its follow-up activity, the Sustainable Water Future Programme, which focuses on this nexus.
At the process level, the GEWEX Atmospheric System Studies (GASS) Panel and the Stratosphere-troposphere Processes And their Role in Climate (SPARC) program will focus on tropospheric-stratospheric processes and exchanges, and on the Grand Challenge on Clouds, Circulation, and Climate Sensitivity.
Improvement in land-atmosphere interactions through better parameterizations, observations, and modeling will be handled by the Global Land/Atmosphere System Study (GLASS) in collaboration with iLEAPS and GHP. This is especially important for the anthropogenic subsurface processes components.
Since water availability is strongly linked to phenomena such as droughts and floods, an overlap exists with the Grand Challenge on Understanding and Predicting Weather and Climate Extremes, presenting another opportunity for collaboration.
