Assessment Of The Impact Of Land Use Land Cover Change On Surface Runoff: A Case Of Debre Markos Town, Ethiopia

Abstract

Urbanization is one of the most pervasive human endeavors, resulting in many physical and biochemical modifications to the hydrological system and its processes. However, the impact of urbanization driven LULC change on surface runoff remains unexplored. This study demonstrates the changes in surface runoff variables due to the changes in LULC during the period 1995-2022. The integration of remote sensing and GIS was applied to automate the estimation of surface runoff and analyzed its trends at different scales based on the SCS-CN model. Landsat TM, ETM+, and OLI/TIRS data from the USGS website was utilized to detect urban land cover changes. The area of each LULC classes in 1995, 2000, 2005, 2010, 2015 and 2022 were determined using supervised image classification approach. Accuracy assessment of image classification was processed using ENVI software and the result revealed that the overall accuracies are 97.2%, 96.6%, 96.8%, 96.4%, 90.33%, and 91.2% with the Kappa Coefficient of 0.96, 0.95, 0.96, 0.95, 0.88 and 0.89 for years 1995, 2000, 2005, 2010, 2015 and 2022 respectively. The increase in comprehensive socio-economic activities has resulted in considerable changes in the LULC of Debre Markos town. The LULC change analysis revealed that the urban area and barren land have increased annually by 17.36% and 3.3% respectively and that of vegetation, agricultural land, and meadow decreased by 1.19%, 1.32% and 0.73% respectively during the study period of 1995 to 2022. The depth and flowrate of direct runoff have increased over study period and the result showed that runoff depth and flowrate of the town increased by 3.7mm and 147.9m3/s respectively from 1995 to 2022. High increase in runoff variables has shown at wuseta watershed than wutrin watershed. Correlation coefficient (R) and coefficient of determination (R2) were computed to explore the associations between imperviousness and runoff variables and the result showed that +0.98 and +0.99 respectively, which revealed their strong direct relationship. Overall, urbanization lowered potential maximum storage, and thus increased runoff coefficient values. An area that experienced more urban growth had a greater potential for increasing surface runoff depth and its flowrate. Runoff responses identified in the spatiotemporal analysis emphasize the importance of monitoring and assessing the hydrological regime in Debre Markos.