A multi-proxy approach to evaluating Drought in Southern Africa: climate, vegetation, and water table

Southern Africa is increasingly vulnerable to long-term drought, particularly in arid to semi-arid regions. However, insufficient monitoring makes the timing and extent of groundwater response to droughts difficult to quantify. Here, we combine evidence of past drought in the satellite record with water table modeling to evaluate the spatio-temporal relationship between agricultural and hydrological drought across Southern Africa from 1981-2025. We use the normalized difference vegetation index (NDVI) from the STFLNDVI dataset as a proxy for agricultural drought. We simulate monthly water table depth (WTD) at 30 arcsecond resolution using the Water Table Model (WTM), which dynamically couples surface and subsurface hydrologic processes. By defining standardized anomalies derived from NDVI and simulated WTD, we aim to examine spatio-temporal drought propagation characteristics between agricultural and hydrological drought. Drought periods are compared against documented droughts to evaluate whether the human experience of drought is reflected in simulated groundwater changes. The goal of this study is to provide a regional assessment of drought propagation into groundwater across Southern Africa and to identify where groundwater systems may be vulnerable to drought.