GIS based water balance components estimation in northern Ethiopia catchment

Abstract

A tool to understand water balance components is crucial for developing water resources management strategies. However, there are inadequate reports on the application of water balance models integrated with Geographical Information System (GIS) at ungauged sub-catchment scale. The objective of this study was to estimate hydrological water balance components using a flexible, physically and GIS based WetSpass water balance model for the Dura sub-catchment, northern Ethiopia. WetSpass model input data included grid files of soil types, topography, slope, land use, temperature, precipitation, potential evapotranspiration (PET), wind-speed and groundwater, and parameter tables (dbf file). Descriptive and Inverse Distance Weighted were used to analyze the different data. Model outputs included actual evapotranspiration (ET), surface runoff and groundwater recharge. The PET of the area was computed using different methods and performance assessment showed < 2% of error, indicating all are robust for supporting decision making. In the study sub-catchment, the mean annual PET and actual ET were found to be 1560 and 576 mm, respectively. The model-estimated annual actual ET was calculated to be 78.4% of the mean annual rainfall. However, there is spatial and temporal variability in ET across the sub-catchment. About 77.5% of the annual actual ET was estimated during the summer season. In the study sub-catchment, about 7.9% and 13.7% of the mean annual precipitation are effective in contributing to groundwater recharge and surface runoff, respectively. On the basis of the model results, the majority of the Dura sub-catchment is generally characterized by low groundwater recharge and high actual ET. The water balance components estimated using the WetSpass model are closely comparable to the observed data as their fitness was showed using R2> 0.90 and D < 5%, indicating that the model outputs are important for supporting decision making. On the basis of the model results, it is thus suggested to introduce and implement appropriate site-specific integrated soil and water management schemes such as water conservation structures that enhance groundwater and reduce runoff in the study catchment conditions.