The influence of land cover and vegetation on the hydrological balance and groundwater recharge in the Northern Cape Province South Africa

Groundwater water levels and the ability of aquifers to sustain water have been reportedly on the decline in specific areas in the Northern Cape Province in South Africa. The study area is located in an arid regional with mean annual precipitation of less than 400 mm/a, which is drought prone. The hydrological balances indicated that the required groundwater recharge to balance is at least 20 times less than the expected minimum natural recharge. Further investigation indicated that evapo-transpiration forms +95% of the hydrological balance. The models were very sensitive to evapo-transpiration, which focused the study towards land use and land cover. Research on land cover provided evidence that bush encroachment of especially alien species (e.g. Prosopis and Acacia Millefelera) could be responsible for increasing evapo-transpiration if compared to natural grassy vegetation with infestation levels of 5% to 8% in the study area. The hydrological models indicated that infestation of 2.5 % is sufficient to capture all the rainfall reducing groundwater recharge to zero. The study shows that infestation in combination with a thick soil cover of Kalahari Sand or associated formations provide a buffer for groundwater recharge as the soils have a high soil moisture retention capacity which is ideal for use by plants, especially deep rooted woody species. More detailed investigations are under way to compare present and historical land cover and evapo-transpiration potential to qualify the findings of the initial study. Land management and mitigation of bush encroachment is recommended to ensure the sustainability of future soil moisture and groundwater recharge.

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Northern Cape
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