Impacts of Climate Change on Water Availability in Zambia: Implications for Irrigation Development

Water resources are important for current and future socioeconomic development of any country. To manage water resources sustainably requires a good understanding of the current and future availability of these resources at local level: how much water is available, where is it available and when? This paper assesses the spatial and temporal distribution of water resources and the impacts of projected climate change on water resource availability, and draws implications for irrigation development in Zambia. Unlike past studies done at national level, this study is at river basin level. Using a water balance model in a hydrological modeling framework and statistical downscaling of future climate scenarios from the Intergovernmental Panel on Climate Change, the paper simulates the impacts of climate change on water availability in Zambia’s main river basins from current periods until the end of the century in 2100. The main results indicate that temperature increases in Zambia are projected to reach 1.9o C and 2.3o C by 2050 and 2100, respectively. Rainfall is projected to decrease by about 3% by mid-century and only marginally by about 0.6% towards the end of the century across the country. However, there are large differences across the different regions, with the southern, western and eastern regions projected to be much more affected compared to the northern region. These changes in rainfall and temperature will reduce water availability by about 13% from current (observed) levels of about 97 km3 to about 84 km3 by the end of the century at national level. At the river basin level, the northern basins are likely to stay the same or experience slight increases in water resources compared to those in the southern and western parts of Zambia. In particular, Zambezi, Kafue, and Luangwa River Basins are projected to have less water resources available due to reduced rainfall and higher temperatures . These findings have implications for smallholder irrigation development in Zambia. First, this implies that contingent on costs, current and future irrigation schemes will need to adopt more water efficient technologies such as overhead irrigation systems (e.g., center pivots and drip irrigation) as opposed to the prevalent surface irrigation methods. Second, reduced water availability will increase access and irrigation costs, which in turn may reduce its profitability among smallholder farmers as they tend to have limited capital and capacity to adapt to higher cost structures. Third, competition for the reduced available water resources will disadvantage the smallholder farmers. Policies to protect them against the large scale users are required. Options for bulky water transfer from low-demand, high-water areas in the north to the high-demand, low-water areas in the south should be explored. Fourth, water resources management and regulation need to be strengthened, for example by ensuring that water user rights and fees become mandatory, even among smallholder farmers. There is also need to improve rain water harvesting and storage by investing in more efficient reservoirs. How these reservoirs should be managed to ensure equitable access to water resources and to reduce water loss due evapotranspiration requires further thought.