WITHDRAWN: Rethinking Urban Planning from the Perspective of Nature-based Stormwater Runoff Management in Hawassa City, Ethiopia

Abstract

A considerable area of land has been turned into a built surface due to urbanization in Ethiopia. Storm-runoff is the impact of land conversion into built areas, which is a threat every rain season in Hawassa city. GI-based urban planning plays a prominent role in runoff management. However, the potential benefit of GI remains unexplored in Ethiopia. This research aimed at evaluating the effectiveness of GI to alleviate stormwater runoff that cities have been suffering from. The i-Tree Eco model with pre-stratified random sampling techniques was employed to analyze the hydrological benefits of GI by considering the vegetation structural variables. The ArcGIS was further used to demonstrate the spatial distributions of annually avoided runoff and potential sites across the study area. The study shows that the total number of trees in the study area is 576,224, which contributes to 20.7% of tree coverage in the city. These trees annually intercepted 1,376,132.8 m3 water and avoided 288,372 m3yr-1 runoff, and in turn economically valued at $680,558 USD. However, the GI elements had different runoff reduction efficiency, according to the morpho-functional characteristics of tree species. GI types with large trees, high leaf area, and high number of broadleaved trees were more efficient. Stormwater runoff could be maximized through the incorporation of adequate GI coverage at the planning stage and proper execution on the ground. Hence, this research is expected to make planners and policymakers rethink the integration of GI with the spatial planning of cities in Ethiopia.