Improved understanding of Okavango Delta inundation using GRACE-derived terrestrial water storage

Hydrologic contributions from the Angolan Highlands sustain the Okavango Delta, one of the world’s largest inland wetlands. Observations show a clear link between the timing, intensity, and seasonal distribution of precipitation in the Highlands and flood extent in the Delta. However, the role of upstream water storage remains poorly understood, largely due to limited and uneven hydrological data. Here, we combine satellite-derived terrestrial water storage anomalies from the NASA Gravity Recovery and Climate Experiment (GRACE) and follow-on (GRACE-FO) missions with precipitation from the Climate Hazards Center Infrared Precipitation with Station dataset to assess interannual drivers of maximum flood extent in the Okavango Delta from 2003–2024. We show that GRACE-based terrestrial water storage explains 62% of the variance in annual inundation extent (90% CI: 32%–83%), outperforming precipitation alone (52%, 90% CI: 18%–80%), and that combining both explanatory variables increases explained variance to 73% (90% CI: 52%–89%). Spatial analyses of terrestrial water storage identify the Angolan Highlands as the key source region to the Delta, consistent with prior hydrological and modeling studies. These findings provide the first demonstration, to our knowledge, of GRACE-based terrestrial water storage improving flood modeling in the Okavango Delta and motivate future work to better monitor water towers driven by both precipitation and subsurface aquifer contributions.