Potential impacts of climate change on groundwater recharge in South Africa using stable isotopes of water

Potential impacts of climate change on groundwater recharge in South Africa using stable isotopes of water

KE Ramudzuli, JA Miller, T. Vennmann, A Watson and JD van Rooyen

Department of Earth Sciences, Stellenbosch University.

Unimodal wet season precipitation plays a significant role in ensuring sustainable and continuous replenishment of groundwater resources, especially in arid to semi-arid climates that only recharge during heavy rainfall events. For this reason, changes in precipitation patterns (i.e., the frequency, intensity, duration and seasonality of precipitation events) may impact the reliability and sustainability of groundwater resources. This study investigates the relationship between the stable water isotope precipitation vs groundwater composition from across different climatic zones in South Africa. The analysis was done to examine the record of evaporation recorded in the stable water isotopes of precipitation before groundwater recharge, in order to extrapolate how variable changes in climatic conditions would translate to groundwater recharge (e.g., induced evaporative loss of rainfall). Both precipitation and groundwater samples showed a strong alignment with the Global Meteoric Water Line (GMWL) and respective LMWLs with a dispersion that increased from the O- and H- isotope depleted sections towards the enriched areas. Groundwater samples generally recorded the same characteristics as wet season precipitation irrespective of whether this was winter or summer rainfall regions, and plotting with the same regionality for Local Meteoric Water Lines (LWMLs). Secondary evaporation of precipitation, noted by the deviation of groundwater samples from the GMWL and respective LMWLs, increased from the south-eastern and east coasts, which receive relatively higher precipitation amounts, towards the interior along with south and west coast of the country, which are somewhat dryer. This analysis will assist in the forecasting of future groundwater recharge patterns in response to climate change and represents an important step in assessing the impact of climate variability on groundwater sustainability.