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Climate change will affect worldwide weather and crop development. Agriculture is a major concern around Groot Letaba catchment (South Africa), and future irrigation supply for avocado crops is at risk but remains unclear. This research focused on the impact of climate change on future irrigation demand of avocados, with a case study in Limpopo province, South Africa. The objective was to compare water demand between the baseline data (1982-2010) and projections for 2050 and 2080 and determine the potential effect of climate change on avocados’ irrigation requirements in the future. First, a weather generator was used to create 1000 future daily time-series of rainfall and temperature, following nineteen different General Climate Models, for two emissions scenarios. The outputs were used in a soil-water balance model to simulate irrigation requirements of avocados according to the different scenarios and years studied. Models’ average irrigation demand was found to increase by at least 8.7% by 2050, and up to 17.4% by 2080, with a notable dispersion of values and few models predicting a decrease. The frequency of exceeding annual irrigation capacity could reach 45% with mitigation and 58% without mitigation by 2080. Farmers are expected to have more difficulties providing sufficient irrigation to avocados trees and facing possible multi-year droughts. Mitigation appeared as essential to ensure the sustainability of avocado business. MSc in Environmental Engineering

South Africa is a water scarce country with future water availability threatened by climate change, an increasing population leading to urbanization, increasing agricultural production, and industrialization. Past droughts have highlighted the country’s vulnerability to drought leading to economic losses in the Agricultural sector, inadequate water, and supply for basic domestic needs and failure to meet ecological water requirements. A case study was carried out in the water scarce, 4,937 km² agricultural intensive Groot Letaba catchment located in the Limpopo province. Water Evaluation and Planning (WEAP) model was used to simulate the water supply system in the catchment, from 1981 to 2016. The Nash–Sutcliffe Efficiency was used to validate the model’s accuracy providing a value of 0.91 and 0.86 during calibration (1981-2000) and 0.69 and 0.65 during validation (2001-2016) for streamflow and Tzaneen reservoir levels, respectively. A reference scenario to assess water resources and water demand sites’ vulnerability should droughts experienced between 1981 to 2016 be repeated under current demand was developed. 10% Agricultural water supply reduction, 50% per capita use rate reduction, Tzaneen reservoir storage increase and rerouting domestic return flow to the river were explored as drought adaptation measures. Drought response measures prevented reservoir drawdown in moderate droughts and delayed drawdown in severe droughts, reducing their temporal extents. Improvements in water resources availability correlated with improving demand coverage and reliability. Pairing drought response scenarios amplified benefits realized resulting in 100% demand coverage and reliability for two demand sites. All drought response measures were insufficient to fully circumvent droughts with a magnitude like the 1992-1996 drought. These findings show that effectiveness of response measures is dependent on the intensity and duration of the drought. MSc in Advanced Water Management