The impacts of climatic variations and human water use on global and regional terrestrial water storage changes

The impacts of natural climate variability and anthropogenic water use on our global water resources can be observed from space by dedicated satellite missions or simulated by global hydrological models. It is, however, difficult to quantify the relative contribution of fundamental drivers of terrestrial water storage (TWS) changes, e.g., due to a lack of data or processes in models and the limited vertical and spatial resolution of satellite data sets. Regions that are challenged by acute or constant water stress, as well as areas with increased flooding risk, would benefit from a better understanding and quantification of the main drivers of surface and sub-surface water storage changes.In this study, we identify the main drivers of TWS changes due to natural and human-induced impacts under changing climate. We analyse almost two decades (2003-2021) of TWS changes simulated by the WaterGAP Global Hydrology Model (WGHM) and compare them to observations from the satellite gravity missions GRACE and GRACE-FO. The relative contribution of individual water storage components to TWS is calculated. At large-scale, their variations are found to correlate with natural processes, i.e. precipitation, evapotranspiration, and river outflow. In addition, the influence of human interventions on the water cycle are identified as episodic and long-term effects on the surface water and groundwater extraction. We analyse the largest river basins (>200.000km2) world-wide to identify regions under acute or chronic water stress.