Rethinking urban planning from the perspective of nature-based stormwater runoff management in Ethiopia

A considerable area of land has been turned into a built surface in Ethiopia. Flooding is one of the destructive consequences of such land conversion in the urban centers of the country. Thus, this research aimed at evaluating the effectiveness of urban green infrastructures to alleviate the impacts of runoff in the urbanized part of Hawassa City, Ethiopia. The i-Tree Eco model with pre-stratified random sampling techniques was employed to analyze the hydrological benefits of green infrastructure by considering the vegetation structure and land surface cover variables. Also, the spatial map that shows annually avoided runoff was created using the spatial interpolation method in the ArcGIS software. The outcome of the model-based analysis shows that 576,224 trees were recorded, which contributes to cover 20.7% of the city's total area. These trees intercepted 137,632.8 m(3) year(-1) rainwater and avoided 288,372 m(3) year(-1) runoff, economically valued at $ 680,558/year. However, the existing green infrastructures of the city had different performances in terms of water interception and runoff reduction efficiency, according to the morpho-functional characteristics of trees. Those green infrastructures with large trees, high leaf areas, and a high number of broadleaved trees were more efficient. Runoff reduction efficiency of the city could be maximized through the incorporation of adequate green infrastructure coverage at the urban planning stage and proper execution of structural plans. Hence, this research is expected to help planners and policymakers rethink the integration of green infrastructure in the spatial planning of cities and towns in Ethiopia.