Basin Scale Analysis of Land Surface Hydrological Processes for Water Management in the Lake Turkana Basin

Abstract:

Lake Turkana is the world’s largest permanent desert lake. It is endorheic and located in the arid lands of Kenya making it very prone to anthropogenic and climatic influences. For the total annual freshwater influx, this lake is highly dependent on the Omo river originating in Ethiopia and providing approximately 80% of the inflow to the lake. The other 20% is provided by the Turkwel and Kerio rivers originating in Kenya. Within the last decade, irrigation expansion plans are underway both in Ethiopia and Kenya. This will, in turn, increase the potential water abstraction from rivers draining into the lake leading to the lake ultimately shrinking. Previous studies estimated that the expansion of irrigated land in the lower reaches of the Omo river could potentially abstract 50% of the river water. This will, in turn, result in a significant irreversible ecological damage to the Lake’s ecosystem. This study aims to assess the implications of irrigation area expansion over the last 20 years on the land surface hydrological processes in the basin. The study employs the Land Surface Model (LSM), Simple Biosphere including Urban Canopy (SiBUC) which can consider the irrigation influence on the land surface through a vertical water and heat balance analysis in a mesh. Gradation of soil moisture from the upstream areas to the downstream was reproduced and runoff to the lake calculated. The model is still in the process of being calibrated to improve the runoff output to consider changes in the lakes water balance. This study will be beneficial to advise on the limit of acceptable changes in the expansion of the irrigated area to prevent irreversible changes caused by the permanent shrinking of the lake.