Groundwater storage dynamics in the Lake Chad Basin revealed by GRACE and a multi-sensor signal separation approach

Abstract:

Groundwater resources, a crucial water supply in the Sahel regions of northern Africa, have to be evaluated to ensure its sustainability. In the last decade, Lake Chad Basin (LCB), experienced extreme variabilities in the surface water, which impacted groundwater levels as studied by different authors. Consequently, evaluating the modes of variability of each compartment of the terrestrial water storage (TWS) plays an essential role in LCB water resources management. Therefore, the main objective of this study is to invert groundwater storage (GWS) over LCB using surface water storage (SWS) derived from satellite altimetry and imagery, soil moisture storage (SMS) from the Global Land Data Assimilation System hydrological model (GLDAS), and TWS inferred from Gravity Recovery and Climate Experiment (GRACE) measurements. Here we apply a proper signal separation approach to extract GWS from TWS, which is taken as observations in a least-squares sense to reconstruct GWS. The analysis of the reconstructed GWS series using correlation coefficient, root-mean-square error, and the Nash-Sutcliffe efficiency, shows an improvement of 114%, 26%, and 147%, respectively, compared to the GRACE-based results. These findings could be crucial in the surface and sub-surface water management over LCB.

Keywords:
GRACE; groundwater; hydrological model; Lake Chad Basin; signal separation