Evaluation of the impact of climate change on the inflow to lubov reservoir; the case of usurhu catchment, swaziland

According to IPCC global average temperature is predicted to increase by 1.4-5.8oC by year 2100. Carbon concentration is expected to increase from 377ppm to 490-1260ppm by the end of the country. In as much as global precipitation is expected to increase however in some regions especially in Southern Africa precipitation is expected to change by ± 20%. The Lubovane Reservoir has been constructed to address water shortage for low income subsistence farmers during the dry season when Usuthu River flows are minimal. To address this constrains a 218m ogee shaped weir across the Usuthu river was constructed to harvest flood water during wet season to fill an off river 155 MCM Reservoir. This development aimed at providing irrigation water for 11500 hectares for mainly sugarcane production. There is no evidence that the impacts of climate changes on stream flows were considered and it is uncertain whether the reservoir will fill up with decrease in surface runoff. Three GCMs (CCMAD2, ECH5D2 and IPSLD2) in Magic/Scengen5.1 version 2 were used to simulate using a calibrated rainfall runoff model (watbal) developed by Yates in 1996. Inputs to the Watbal model were year 2075 rainfall and potential over transpiration and current runoff. Simulation results revealed an average of 4.83% and 4.13% decrease in annual runoff for dry and wet-year condition respectively compared to present situation. With initial reservoir storage of 0 to 10% in year 2075, the reservoir will not fill up and the irrigation of 11500 ha will face challenges. This is however not attributing to climate change but mainly due to the limiting size of the diversion canal.