Browsing by Author "Nenweli, Ritshidze"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Evaluating groundwater storage changes under drought in the Western Cape using satellite and in-situ data
    (Stellenbosch : Stellenbosch University, 2023-03) Nenweli, Ritshidze; Chow, Reynold; Watson, Andrew; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: The Western Cape is a water scarce province of South Africa and has become more reliant on groundwater over the last few decades due to frequent droughts, which are anticipated to worsen in the future. While data on surface water use and storage levels in reservoirs are easily accessible throughout the year, the impact on groundwater storage at the provincial scale has not been evaluated yet. However, lack of monitoring boreholes, discontinuous measurements, unavailable monitoring data, and installation of boreholes without proper licensing has made it difficult to manage groundwater sustainably in the region. Remote sensing from National Aeronautics and Space Administration’s Gravity Recovery and Climate Experiment (GRACE) provides continuous and freely accessible datasets through which trends and variations in groundwater storage can be estimated. This research aims to understand how GRACE and Global Land Data Assimilation System (GLDAS) data can be used to monitor groundwater storage in the Western Cape. In-situ groundwater storage declined prominently in the Western Cape during droughts (2003-2006, 2009-2011, 2015-2018 and 2017-2019). While some aquifers are recovering, others (e.g., Vanhynsdorp Aquifer) are still declining, possibly from over-abstraction for irrigation. GRACE TWS (JPL-M) anomalies showed positive moderate correlation (r = 0.69) with in-situ groundwater measurements from the Adelaide Subgroup Aquifer possibly because of the unit’s large areal extent, unconfined nature, and large groundwater storage fluctuations. While the Table Mountain Group Upper Aquifer Unit (TMG UAU) and Cape Flats Aquifer both showed significant positive correlations with GLDAS CLSM (catchment land surface model) groundwater storage of 0.83 and 0.73, respectively; possibly because they are unconfined and their fast response to precipitation. GRACE TWS anomalies have the potential to monitor groundwater storage of the Adelaide Subgroup Aquifer, while GLDAS CLSM groundwater storage data has the potential to monitor groundwater storage of the unconfined TMG UAU and Cape Flats Aquifer. GRACE and GLDAS CLSM groundwater storage data have the potential to monitor groundwater in other parts of South Africa or data scarce regions of Africa to ensure that future generations have access to groundwater.