SIMULATION OF WATER SUPPLY AND DEMAND IN KIPKAREN RIVER SUB-CATCHMENT OF UPPER NZOIA CATCHMENT

Abstract

Water allocation and planning have faced significant challenges globally, particularly in sub-Saharan Africa, where rapid population growth, climate change, and insufficient infrastructure exacerbate existing pressures. This study focused on the Upper Nzoia Catchment in Kenya, specifically the Kipkaren Micro-Catchment, which is experiencing rising water demand and variability in supply. The primary objective was to simulate water supply and demand, assess current availability, model future scenarios using the WEAP Model, and determine optimal allocation strategies for the period 2020–2050. The study is grounded in theoretical frameworks including Integrated Water Resources Management (IWRM), Simulation and Modeling Theory, and Decision Support Systems (DSS). Using a mixed-methods approach, the research collected data on hydrological conditions and sector-specific water demands—agriculture, domestic use, industry, and livestock. This data was integrated into the WEAP model, which was calibrated using historical streamflow records to improve accuracy between simulated and observed results. Scenario analysis included a Reference Scenario, High Population Growth, Increased Agricultural Capacity, Extended Dry Climate, and Wet Climate Sequence. These scenarios accounted for land use changes, climate variability, and population growth trends. The model analysis included evaluation of key parameters and statistical comparisons across scenarios. Results showed strong model performance, with high Nash-Sutcliffe efficiency, r², and correlation coefficients during both calibration (1990–2000) and validation (2001–2010). Streamflow analysis (1959–2019) revealed high variability, with a projected peak flow of 554.87 m³/s in 2024 and minimums down to 6.35 m³/s. Seasonal variation was evident, with October showing peak flows. In 2019, domestic water demand was approximately 9,796 m³/day for a population of 287,000, while agricultural demand reached about 100,200 m³/day. The study found that total demand exceeds average availability during dry periods. Scenario projections showed demand may rise from 71.5 million m³ in 2019 to about 114.3 million m³ by 2050, particularly under drier climate or high-growth scenarios. These findings emphasize the impact of seasonal and climate-driven variability and the risks of water shortages without adaptive planning. To address these challenges, integrated strategies are recommended, including water conservation measures, rainwater harvesting infrastructure, and broader implementation of IWRM. The WEAP model proved effective for simulating water dynamics and informing future planning. The study contributes to the broader understanding of water resource management in the region and highlights the need for further research into remote sensing, adaptive decision support systems, policy evaluation, and the socio-economic implications of water scarcity.