Satellite-based investigation of water stress at the basin scale: an integrated analysis of downscaled GRACE estimates and remotely sensed data

Freshwater availability is a very determining issue, especially in semiarid and arid regions, for sustainable development and secured food production. In this premise, the detection and assessment of water stress are of utmost importance. In this study, the satellite-based Potential Available Water Storage (PAWS) index is used to test its feasibility for a basin-scale analysis of water stress in the Western Mediterranean Basin (WMB) in Türkiye. The coarse-resolution GRACE (Gravity Recovery And Climate Experiment) estimates were downscaled based on the Random Forest (RF) model and then were integrated with fine-resolution precipitation data to derive fine-resolution PAWS values. The accuracy of the index was validated against the net water flux (NWF) and water storage deficit (WSD) values over the basin. The results revealed a good performance for the PAWS index for a local scale evaluation of water stress. The PAWS variations turned out to be highly correlated with the NWF (r = 0.72) and WSD (r = 0.66). The PAWS indicates that the WMB has suffered from a critical hydrological situation from 2003 to 2020 during which the basin has been under stress with the most critical situation in 2018 when the per capita water has fallen below 500 m3 suggesting an absolute water stress status.