Assessing basin scale irrigation potential in the Kafue catchment under global warming levels

Climate change threatens the agriculture sectors of many countries and irrigation is often proffered as a potential adaptation strategy. However, the viability of irrigation as an adaptation strategy depends on the availability of water for irrigation, and this is not assessed in many climate change impact assessments for the agricultural sector. In this study, we assess the hydrological potential of the Kafue catchment in Zambia to sustain and increase agricultural production through the implementation of large-scale water storage and irrigation under climate change. We use a 5-member ensemble of global circulation models to assess the changes in hydrologically relevant variables under 1.5°C, 2.0°C and 3.0°C global warming levels (GWL). These were used to assess the changes in crop water demand (CWD), irrigation water need (IWN), water availability (WA) and the difference between water availability and irrigation water needs, here referred to as basin irrigation potential (BIP) for each GWL. Results show high spatial variability in precipitation in the catchment under current conditions, with corresponding changes under the GWL levels. Changes in precipitation under all levels are inversely related to the current amounts of rainfall with highest rainfall areas having the highest decreases in rainfall while lower rainfall areas projected to have increases in rainfall. CWD is highest in the south of the catchment and follows both the rainfall and temperature gradients. Under climate change, the CWD is projected to increase for all considered global warming levels with the highest increases in the south, resulting in increased IWN. WA will decrease for the most part of the catchment against a decreasing BIP. It is therefore concluded that limiting global warming to 1.5°C will have minimal impact on potential for irrigation in the Kafue catchment. Long-term planning for irrigation development in the catchment should therefore consider these potential impacts to avoid maladaptation.