COMBINED EFFECT OF CLIMATE AND LAND USE LAND COVER CHANGES ON HYDROLOGY: GILGEL ABBAY WATERSHED, ETHIOPIA

Abstract

This study aims to evaluate the impacts of climate and land use change on the hydrology of Gilgel Abbay’s watersheds using the Soil and Water Assessment Tool (SWAT). The study analyzed the hydrologic impacts of climate and land use changes in two ways. The first aspect consists of characterizing hydrological changes two historical land use maps (Land Sat_8 1985 and Land Sat_8 2015) were used to represent land use change on the watershed, and historical climate datasets (1986-2012) was used to create SWAT models for Gilgel Abbay watershed. Land use change detection was done using remote sensing techniques and the maps were processed using ERDAS Imagine 14 and Arc GIS 10.1 software. Climate and Land use are two main factors directly influencing the hydrological processes of the watershed. Gilgel Abbay watershed. RCP 4.5 scenarios were used to project the future climate of 2030’s, and 2060’s. An increase in precipitation from 67.01 mm to 165.03 mm in the 2030’s and decreases from 136.79 mm to 82.96 mm at the period during 2060’s. An increase of average annual maximum temperature is expected to increase 2.3°C in 2030’s while for the period of 2060’s the maximum temperature is expected to increase by 2.9°C, respectively, in future periods. Similarly, average annual minimum temperature is expected to increase by 1.9°C in 2030’s while for the period of 2060’s the minimum temperature is expected to increase by 2.1°C.Combined effects of land use and climate changes showed that 229.87 m3 /s for baseline, 95.57 m3 /s more in 2020-2049, and 70.69 m3 /s more in 2050- 2079 for stream flow compared to climate change scenarios. The combination of climate and land use changes would lead to an increase in stream flow (-63.55% to 24% in 2020-2049 and -54.98% to -4.67% in 2050-2079). SWAT outputs to baseline run (1986-2012). Climate and the land use land/cover change and its driving force on Gilgel Abbay watershed using LANDSAT_8 image to produce two the hydrological model result indicates that the flow was sensitive to land cover change by reducing base flow and increase peak flow this is due to increase agricultural land and deforestation.