Assessment of the Impacts of Climatic variables on the Lower Usuma Reservoir

This study evaluated the impact of climate variables on the volumes of the Lower Usman Reservoir. The anticipated reservoir inflow, outflow and storage capacity based on the future climatic variable scenarios was investigated. Possible trend scenarios for mean temperature, precipitation, evapo-transpiration and reservoir water level for a 21-years period (2000 to 2020) were determined using Mann Kendall and Sen’s slope. Time series of monthly runoff was simulated for this period consequent upon which the reservoir water level was modeled as a function of temperature, precipitation and evapo-transpiration using Artificial Neural Networks. The modeling output indicates that precipitation, evapo-transpiration and reservoir water level exhibited positive trends at Lower Usma River while temperature exhibited a negative trend. This is with absolute assumption that land-use and land-cover effect on the area under study remained unchanged. Also, water resource feeding application through engineered channelization of precipitation and associated flooding and surface runoff harvesting activities, diverting water to the reservoirs, were observed as a contributing factors to the positive trend of the reservoir water level. The reservoir water level estimated with the Artificial Neural Networks forecast differed by 0.73m3 from the historical value. In the overall analysis, there is an indication of sustainability tendency of the reservoir to furnish public water supply and irrigation. However, the significance of these parameters as rightly capturing the influence of climate and effect, on the reservoir in the region is under continuous research.