Grace-Based Observations for Near Real-Time Assessment of Groundwater Drought Severity Index

We propose in the this contribution a satellite-based method for regional assessment of the Palmer-type index of groundwater drought severity (GDSI) at monthly time scale in the North-Western Sahara Aquifer System (NWSAS). The proposed method is based on groundwater storage anomalies derived from GRACE satellites (Gravity Recovery And Climate Experiment) and GRACE Follow On (GRACE-FO) observations, combined with global hydrological models. We have applied an efficient strategy to estimate a (1°x1°) grid-cells time-series of GGDI (GRACE Groundwater Drought Index) from these anomalies, based upon a statistical analysis and procedures to filter out the anthropogenic trends. In second step of our methodology, an approach based on wavelet coherence was applied to the GGDI grid-cells to perform the climate teleconnections analysis, to detect an eventual relationship with climatic factors inducing extreme climate events. By comparing the obtained GGDI along NWSAS regions to other hydrological drought indices as PDSI (Palmer Drought Severity Index) and SPEI (Standardized Precipitation-Evapotranspiration Index), we have allowed us to highlight the performance of the proposed method to monitor in near-real time the droughts/floods events occurred on the studied area. The obtained results have also revealed the existence of some correlation between the GGDI and ENSO time series and other climate indices not presented herein, reflecting some periods of drought/flood, occurred in different regions of NWSAS. These findings can be a novel information support to evaluate the natural effects on the groundwater recharge and depletion rates.