Impact Of Climate Change On Hydrology And Water Resources In The Upper Zambezi River Basin

Abstract

According to the Inter-Governmental Panel on Climate Change (IPCC), the Southern African region is regarded as one of the most vulnerable regions in Africa. The Zambezi River Basin (ZRB), the largest basin in Southern Africa is characterised by spatial and temporal rainfall variability, and in some cases, scarce water resources. Climate change is likely to affect nearly every aspect of human well-being; from agricultural productivity and energy use to flood control, municipal and industrial water supply to wildlife management. There are few studies focussed on hydrology and climate change at a local catchment scale in the ZRB, therefore, this research sought to investigate the severity of the impacts of climate change on hydrology and water resources for the purposes of evaluation for sustainable planning and management of the resources. The review of water resources linkage to climate variability showed occurrences of floods,droughts,uneven distribution of water resources,rising temperatures and high evapotranspiration rates. The technology of using Climate Forecasting System Reanalysis (CFSR) data to estimate water resources in data scarce regions such as Southern Africa showed results that were satisfactory. Providing Regional Climate Impact Studies (PRECIS) model results proved to be reliable with a sufficient model skill that predicted an increase in rainfall and temperature while predicting a decrease in other areas within the same basin. The results from six downscaled bias-corrected Global Climate Models (GCM) were focussed on 2020-2050.The results under RCP4.5 climate scenario, predicted a seasonal increase in rainfall,runoff and water yield in December, January and February (DJF) while the changes in the rest of the seasons were generally insignificant. The annual rainfall was predicted to decrease by 0.7% while water yield and runoff would increase by 5% and 6%, respectively. The results under RCP8.5 climate scenario predicted seasonal increases of runoff at 211% and rainfall at 35% indicating a strong likelyhood of occurrence of an extreme flood event. Annual statistics show a significant increase of 65%, 40% and 19% in runoff, water yield and rainfall, respectively. The basin under RCP4.5 climate scenario is predicted with insignificant changes with baseline in monthly, seasonal and annual flow regime. The majority of GCMs under RCP8.5 climate scenario indicate 4-8% increase in streamflow while the intra-annual and inter-annual streamflow variability will increase by a considerable margin. There is also a significant increase in seasonal streamflow that ranges between 34 - 134%. The future climate change impact studies need to focus on RCP4.5 and RCP8.5 for 2050-2100 in order to assess and evaluate any possible future impact on hydrology and water resources.