Climate Change in the Niger Basin on Hydrological Properties and Functions of Kainji Lake, West Africa

Abstract

The Niger River Basin - home to over 100 million people - is a vital and complex asset for West Africa. Since the 1970s, the basin has been characterized by hydro-climatic changes with significant impacts on water resources. Climate change could potentially have large impacts on water availability in the basin, but its effective simulation is hampered by inadequate and diminishing number of reliable observation stations. Climate simulations in the basin have also been difficult to handle with existing models due to the complexity and diversity of processes to be represented. No consistent trend for either decreasing or increasing precipitation emerged from global climate model (GCM) products. Countries in the Niger River basin (West Africa) are planning to invest millions of dollars in the expansion of hydropower in the nearest future. With the impacts of climate change in the basin already occurring, there is a need to comprehend the influence of future hydro-climatic changes on water resources and hydro-power generation in the basin. This thesis integrates opinions of local populations with scientific approach in the evaluation of impacts of climate change on water resources in the Niger basin. The consistency of indigenous perceptions and adaptive responses to rainfall and river discharge observations was evaluated in the Niger Basin. Socioeconomic data were collected from 239 households in 30 communities across two settlements in the Niger basin. Historical data on rainfall and river discharge from 1950-2010 were analyzed and agreement with local perceptions assessed. Future climate trends were assessed with 8 GCMs and two emission scenarios (RCP4.5 and RCP8.5) from the Coordinated Regional Downscaling Experiment (CORDEX - CMIP5) framework. Future trends (2010-2100) and influence of bias correction on projected climate patterns from the 8 GCMs were also evaluated. Consequently, a hydrological model was adapted and used to evaluate impacts of climate change on runoff under present and future conditions. To determine impacts of climate change on hydropower production, a hydro electricity model based on gauged observations from the largest hydroelectricity dam (Kainji) in the Niger basin was developed. There was close agreement between observations and perceptions. Indigenous perceptions gave good indication of the most vulnerable sectors as well as communities who displayed the greatest willingness to combat climate change. Climate change will drive about 5-10% ensemble median increase in precipitation with high spatial variability in the Niger basin. Larger parts of this increase in precipitation will be experienced in the Sahelian region. Close GCM agreement on projected precipitation pattern shows great confidence in the CMIP5 projected precipitation pattern across the Niger basin. Bias correction improved the quality of rainfall projections from the 8 GCMs by improving their fitness to the observed. Means of 0.74(NSE), 0.92(d), 0.80 (md), 0.89(r), 0.79(R2) and 0.76(KGE) were recorded for climatological comparison between GCMs and satellite modeled observed precipitation before bias correction while means of 0.86(NSE), 0.97(d), 0.86 (md), 0.93(r), 0.87(R2) and 0.92(KGE) were witnessed after bias correction. The improved IHACRES hydrological model presented in this thesis showed high suitability for the basin based on recorded high calibration (0.73(NSE), 0.92(d), 0.74 (md), 0.85(r), 0.73(R2) and 0.81(KGE)) efficiency coefficients. Climate change will drive increase in precipitation, temperature, PET on the Niger basin and runoff at Kainji and Malanville. Close GCM agreement on projected increasing runoff pattern in the basin shows great confidence in the modeling framework presented in this study. The invented hydropower model displayed high calibration (0.81(NSE), 0.94(d), 0.81 (md), 0.95(r), 0.90(R2) and 0.75(KGE)) efficiency coefficients between observed and simulated Kainji lake reservoir level which gives great potential for its applicability in the basin. Climate change will drive about 50MW (RCP4.5) and 100MW (RCP8.5) ensemble median annual average increase in hydropower production in the Niger basin. This potential could be positively exploited by expanding water storage for hydropower production, in parts of the basin where there will be significant increase in discharge as witnessed upstream the Kainji lake.