SURFACE WATER POTENTIAL AND DEMAND SCENARIO ANALYSIS: A CASE STUDY OF DIJO WATERSHED, CENTRAL ETHIOPIA

Abstract

Insufficient understanding of the available water resources and inadequate coordination in their management frequently lead to competition among users for these limited water resources. This study assessed surface water potential and water demand in the Dijo watershed to optimize benefits while maintaining ecological requirements. To achieve this goal the SWAT model was used to analyze surface water potential, following sensitivity analysis, calibration, and validation using SWAT_CUP. Additionally, the Water Evaluation and Planning (WEAP) model was utilized to determine water demands. Various scenarios were developed to analyze future water demand, supply requirements, and unmet demand from 2025 to 2050. The determination of water demand for crop water requirements and irrigation water requirements was conducted using the CROPWAT 8.0 model. The results showed that the available surface water potential in the watershed was 411.31 MCM in 2024. calibration and validation results showed satisfactory performance, with R² = 0.73, NSE = 0.68, and PBIS = -4.7 for calibration, and R² = 0.79, NSE = 0.62, and PBIS = -9.1 for validation. The analysis conducted during the study period of 2024 revealed that the water demands were 20.54 MCM for domestic consumption, 2.054 MCM for industrial activities, 35.06 MCM for irrigation, 12.54 MCM for livestock, and 41.13 MCM for environmental flow requirements. The total water demand for the year 2024 was recorded at 111.33 MCM, accounting for 27% of the surface water potential available and there was no annual unmet demand; however, shortages occurred in November, December, and January due to low flow conditions. The study recommends harvesting rainfall during the rainy season to mitigate shortages in November, December, and January. The reference scenario was projected in two time horizons, the total water demand will increase to 125.8 MCM in 2035 and 156.92 MCM in 2050. For a high population growth scenario, the total water demand will increase to 133.11 MCM in 2035 and 187.85 MCM in 2050. For the irrigation farm expansion scenario, the total water demand will increase to 134.34 MCM in 2035 and 180.54 MCM in 2050. For the combination scenario(both High population growth rate and Irrigation farm expansion), the total water demand will increase to 141.62 MCM in 2035 and 211.43 MCM in 2050. Keywords: Dijo watershed, SWAT, WEAP, CROPWAT, SWAT_CUP water demand, and