Analyzing the impacts of urbanization on runoff characteristics in Adama city, Ethiopia

Abstract Background It has been increasingly recognized that urbanization is responsible for alterations of land use/land cover globally with substantial environmental impacts on all temporal and spatial scales. Particularly, it significantly affects the hydrologic cycle. Floods are the major threats to several cities worldwide with more effects in developing countries. Likewise, urban water management has become the main focus of sustainable urban development and poses higher demand for information related to the interaction between the urbanization process and hydrological attributes, but little is known in the context of Ethiopian urban centers. For this, Adama city, a fast grown and flood vulnerable urban area is considered to examine the impacts of urbanization on the storm runoff at different spatial scales from 1995 to 2019. Preparing land use/land cover (LULC) maps for different periods, the dynamics of LULC transformations were analyzed. The SCS-CN method was used to compute runoff at respective years from which spatiotemporal changes of the city’s hydrology were assessed at the city and watershed levels. Regression analysis was used for exploring the relation between the spatiotemporal changes of imperviousness ratio and runoff.Results The findings show that the urban built-up area undergone about 22% expansion annually from 1995 to 2019. Besides the runoff is increased by 23% in the City and 31% and 16.6% in the watersheds. Moreover, the significant direct linear relationship is found between the spatiotemporal variations of runoff and imperviousness ratio at both spatial scales.Conclusions Adama city has experienced significant LULC transformations over the last 24 years with significant effects on hydrological attributes, which pressed an alarm for increasing flood hazards. Hence, in order to realize sustainable growth of the city, future developments should be guided by impervious surface-based land use regulations.