Estimating water storage change from GRACE satellite data over the Breede Water Management Area, Western Cape, South Africa

Abstract Groundwater levels in the Breede Water Management Area (WMA) have steadily declined, driven by climatic extremes and anthropogenic pressures. The lack of representative aquifer storage parameter values, inadequate groundwater monitoring wells, and inconsistent observation networks complicate the assessment of groundwater storage changes. This study employs GRACE (Gravity Recovery and Climate Experiment) satellite data, complemented by GLDAS (Global Land Data Assimilation System) soil moisture and surface water data, to estimate groundwater storage anomalies (GWS) in the Breede WMA from 2009 to 2022. Despite the region’s sparse monitoring network, GRACE-derived GWS was validated using limited in situ measurements, showing a strong negative correlation ( r = −0.84). Results indicate a cumulative groundwater storage loss over the 14-year study period (2009–2022), corresponding to an average annual decline in groundwater levels of 0.08 cm. This decline is attributed to decreased precipitation, the expansion of irrigated agriculture from 2009 to 2020, and increased groundwater abstraction for water-intensive crops. These factors, compounded by limited recharge during drought periods, highlight the vulnerability of the region’s fractured bedrock aquifers to over-exploitation. The study demonstrates the potential of GRACE satellite data to assess groundwater storage in regions with limited monitoring infrastructure. Findings emphasize the need for integrated water resource management (IWRM) strategies, including improved irrigation practices, enhanced groundwater monitoring and policies to regulate abstraction. This research contributes towards understanding groundwater dynamics in semi-arid regions and provides a foundation for sustainable resource management in water-scarce areas like the Breede WMA.