A groundwater drought indicator for South Africa
Vermeulen, Lendl Marcell
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South Africa experienced one of its most severe droughts from 2014 to 2016. The drought affected water resources in the country, and signs of recovery were first observed in 2019. Droughts circulate through the hydrological cycle and affect both surface and groundwater resources. Drought indices (DIs) are used to analyse and identify drought periods. All DIs require accurate and complete data sets, such as precipitation. Drought indices like the standardised precipitation index (SPI) and the standardised groundwater level index (SGI) are precipitation-based and groundwater-level-based. The SGI required complete groundwater level data sets in order to perform the simulation. Groundwater balance models were used to simulate groundwater levels, where insufficient groundwater level data was present in the selected study areas. Therefore, a developed index namely the groundwater drought strength index (GDSI) was used to accommodate the lack in data. The study areas were identified based on their geologies, in order to assess the developed groundwater drought indicator’s ability to indicate groundwater droughts in different lithologies. Groundwater droughts were distinguishable, provided that the lag between rainfall and recharge were taken into consideration. The trend of groundwater level simulations was found to be an added benefit in understanding how groundwater levels responded to climatic conditions. The results showed groundwater drought periods and periods of groundwater level decline. By identifying these periods, sustainable management of groundwater resources can be implemented with the use of a groundwater drought indicator.