THE EFFECT OF LANDUSE/LAND COVER CHANGES ON WATER BALANCE COMPONENTS USING QSWAT MODEL: A CASE STUDY AT SHAYA WATERSHED, ETHIOPIA

Abstract

Ethiopia has experienced considerable land-use/land cover changes which altered the hydrological processes in many watersheds due to expansion of agriculture and population growth. This change can affect the water quality and quantity in space and time; thus, contribute to the deterioration of living conditions. Therefore, to address this concern, the semi-distributed model must able to reveal the effect of land-use/land cover changes on water resources for integrated watershed management. In this study, the change in land-use/land cover at Shaya Watershed in Genale-Dawa River Basin were evaluated by ERDAS IMAGINE software and using satellite image data (Landsat 5TM,7ETM,8OLI) for the proposed four land classification (1989,2002,2011,2019). The dominant classes were classified such as agriculture, forest, shrubland, grassland, bareland and settlement. The overall kappa statistics of land-use/land cover classification for each of the land map were found to be in the range of acceptance criteria based on literature (i.e. > 0.8). The result revealed that forest, grassland, bareland and shrubland coverage decreased from (38.47% to 27.84%), (18.8% to 8.92%), (3.26% to 1.12%) and (16.55% to 15.53%) between (1989-2019) period respectively. Whereas, agriculture and settlement coverage increased from (20.41% to 38.38%) and (2.54% to 8.25%) in the same period. The QSWAT model has been used to estimate water balance components under land use/land cover phases. The calibrated and validated of this model performance were evaluated based on R2 , NSE and PBAIS values which indicated good agreement between observed and simulated discharge. The effect of land-use/land cover changes were assessed by four land scenarios in which climate data (1989-2018), soil map and slope map were kept same, and only the land-use map were changed. The result showed that land-use/land cover have resulted in corresponding increase in surface runoff to streamflow, and decrease in base flow to streamflow and lateral flow to streamflow. Surface runoff to streamflow has increased from (26.4% to 30.7%), and base flow to streamflow has decreased from (65% to 61.1%) in the period of (1989- 2019). But, slightly decreased were seen in lateral flow to streamflow from (8.7% to 8.2%) in the same period. In addition, surface runoff increased by (14% & 2.8%) in rainy season(kiremt) and dry season(bega) while groundwater flow decreased by (11% & 6.3%) in the same season. The total flow increased by (1.6%) in kiremt and decreased by (3.9%) in bega; whereas ET increased by (0.4% & 0.8%) in kiremt and bega season. The change in water balances had been observed in past 30 years due to the factor of land-use/land cover changes in the watershed. The output of this study could be used for soil and water conservation in Shaya Watershed.