Climate change implications on water availability and crop production: Exploring adaptation strategies in the Olifants River basin, South Africa

Abstract

Climate change is expected to have direct and indirect impacts on water resources and agricultural production systems, which potentially threatens the livelihood of local, regional and global population as well as the economy. The level and trend of the impact caused by climate change is dependent on the specific location and adaptive capacity of local communities and food producers. The main aim of this thesis was to evaluate the impact of climate change on water availability and crop production as well as to assess the extent to which adaptation strategies can mitigate the impact in the Olifants catchment, South Africa. To achieve the stated aim of this study, three research objectives were analysed. - The first objective evaluated the impact of climate change on water availability and assessed the extent to which a range of adaptation measures can mitigate the impact. - The second objective investigated smallholder farmers’ perception of climate change and their adaptive responses using a questionnaire-based interview. - While the third objective quantified the impact of climate change on crop production and evaluated possible agricultural management practices adopted by farmers to improve current and future crop yield using a processed-based crop model. This model was driven by high resolution climate change simulations for current conditions (1975-2006) as well as future climate projections (2010-2039), (2040-2069) and (2070-2099) for representative Concentration Pathways (RCPs), RCP4.5 and RCP8.5. The findings of the first objective revealed that climate change is expected to cause an increase in temperature of 1℃ to 4℃, with precipitation decreasing by 5% to 30% for both RCP4.5 and RCP8.5 respectively. Results further revealed that water demand will not be met in the future due to increasing socio-economic development, coupled with decreasing streamflow resulting from increased temperature and decreased precipitation. In addition, results from the assessment of adaptation strategies indicated that the combination of management strategies provided a better and more efficient solution to water scarcity issues arising from climate change. The findings of the second objective showed that about 98% of smallholder farmers were aware of climate change. Their perception of these changes aligns with actual meteorological data of decreasing inter-annual rainfall and an increasing temperature trend. Results also revealed that 90% of smallholder farmers adopted several adaptation measures, among which, the use of improved seed varieties, application of chemical fertilizer, and changing planting dates, were the most commonly practised. Finally, the findings of the third objective revealed an increase in crop water requirement and a decline in crop yield, ranging between 19-65%, 11-38%, 16-42% and 5-30% for maize, soya beans, dry beans, and sunflower, under both RCPs climate change scenarios. The decline in crop yield was attributed to the increase in temperature accompanied by a decrease in precipitation. Among the various agricultural management practices (shifting of planting date with the application of full irrigation, use of irrigation efficiency techniques, application of deficit irrigation water, and the use of rainwater harvest) were evaluated to minimize the negative impacts of climate change, the integration of altering the planting date with the application of full irrigation as well as the use of rainwater harvest was found to be more effective in improving crop yield under the impact of climate change. The overall findings of this study provide insight to policy makers on the most appropriate strategies to be implemented in order to ensure future water resources and crop production in the context of climate change.