Urban land cover and morphometric analysis for flash flood vulnerability mapping, and riparian landscape conservation in Kebena river watershed, Addis Ababa
The city of Addis Ababa has a degraded stream ecosystem and its watersheds are exposed to redundant flash floods that can destroy the existing urban infrastructures and utilities. This research aimed to map flash flood vulnerability of the watershed inside Addis Ababa, and evaluate the status of the riparian landscape. Methodologically, the study employed the Biophysical Composition Index (BCI) to detect the impervious surface, and the Normalized Difference Vegetation Index (NDVI) to classify the vegetation cover. Arc-hydro tool was used to identify the micro-watersheds and measure the morphometric factors then principal component analysis (PCA) elucidates the most important factors, and the fuzzy overlay analysis combined land cover and morphometric analysis result to produce the final flash flood vulnerability map. Moreover, riparian buffering 15, 30 and 90 m distances were defined to measure the degree of imperviousness, greenness and vulnerability to flash flooding. Accordingly, 969 hectares of land were depicted within the watershed as flash flood vulnerable areas. These are primarily found in the southeastern and southwestern parts where impervious land cover prevailed, and the northwestern portion where extremely rugged terrain covered by reduced vegetation. In all buffering distances the proportion of impervious surface is greater than the vegetation cover. Even within 15m buffering distance, which was set as the national urban planning standard. It is concluded that Kebena watershed is vulnerable to flash floods as the riparian landscape dominated by impervious and depleted vegetation cover. Integrating multiple geospatial techniques is helpful to devise a method for sustainable riparian landscape monitoring.