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

Urbanization is a global trend with a substantial environmental impacts, particularly hydrologic cycle. With this respect, storm water management has become the main target of sustainable urban development and has posed the higher demand for information related to the interaction between the urbanization process and hydrological attributes in both temporal and spatial scales, but little is understood in the context of Ethiopian urban centers. For this, the fast grown and flood vulnerable urban area, Adama city, is considered to evaluate the hydrologic influences attributable to urbanization. By preparing the land use/land cover (LULC) maps of the study area for different periods, the dynamics of LULC transformations were analyzed. The SCS-CN method was employed to determine the runoff at respective years, and the spatio-temporal changes of runoff were assessed at the city watershed and its sub-watersheds. The relation between the spatio-temporal changes of imperviousness ratio and runoff depth was explored through regression analysis. The findings show that the urban built-up area undergone about 22% expansion annually from 1995 to 2019. Likewise, the runoff depth is increased by 9.5% in the City administration and 12.9% and 6.9% within the two sub-watersheds. The results also reveal that at all spatial scales, the temporal change of runoff depth is linearly associated with the rise of imperviousness ratio. This study would help planners in the formulation of effective land use plan to manage the hydrological influences of urbanization, thereby supports the efforts being made to ensure the sustainable development of urban areas.