Document Type : Special Issue: New Approaches to Water and Soil Management and Modeling
Authors
1
Ph.D. scholar of Hydraulic Engineering, Faculty of Hydraulic & Water resources Engineering, Arba Minch University, Arba Minch, Ethiopia
2
Professor, Faculty of Hydraulic & Water resources Engineering, Arba Minch University, Arba Minch, Ethiopia
3
Associate Professor, Faculty of Hydraulic & Water resources Engineering, Arba Minch University, Arba Minch, Ethiopia
Abstract
Evapotranspiration (ET) is the second most important element of the hydrological cycle after rainfall. Despite rising attention in hydrological responses to environmental change, limited extensive evaluations of AET have been conducted in the study watershed that integrates the combined influences of LULC and climate change. Previous research has largely focused on broader areas, such as the LTSB and the Abbay Basin, offering a limited understanding of localized relations between these factors. Therefore, this study investigates the synergistic impacts of LULC dynamics and climate change on AET within the Guna Tana Watershed (GTW) using the physically based MIKE SHE hydrological model, aiming to improve understanding of watershed-scale hydrological responses under future environmental conditions. ENVI 5.3 and QGIS 2.18.15 were used to assess the LULC classification and prediction, respectively. Ensembles of GCM were used after bias correction, and calibration of the model was done using streamflow. Agriculture was expanded from 2047.02 km2 to 2268.82 km2, whereas forest will decline to 103.38 km2 from 127.64 km2 in the 1991-2021 period. Built-up showed the least amount of coverage (0.02%, 0.11%, and 0.31%). The results of the calibration and validation show that MIKE SHE is capable of modeling the AET effectively. Excellent results were indicated in two watersheds by both calibration and validation (R =0.87-0.94). The rise in AET may be detrimental to the watersheds because it reduces streamflow and groundwater recharge. Moreover, soil moisture stress increases the risk of drought. Projected changes in AET relative to the baseline period indicate increasing trends in both the Gumara and Ribb watersheds under future climate scenarios. In the Gumara watershed, mean annual AET is expected to rise moderately, with increases of 3.25% and 1.19% in the 2020s and 2050s under SSP2-4.5, and 5.09% and 8.01% under SSP5-8.5. The Ribb watershed shows a stronger response, with AET increasing by 16.92% and 19.30% under SSP2-4.5, and 14.13% and 22.07% under SSP5-8.5. All of this presents problems for the environment and water balance downstream, such as Lake Tana. Future research should include additional climate models and ground truth data regarding plant characteristics to increase model accuracy and reduce uncertainty.
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