Integrated AHP and GIS based flood risk assessment and mapping in Wonji area of Awash River Basin, Oromia Region, Ethiopia

Abstract

Flooding poses a significant threat to communities, agricultural systems, and infrastructure in low-lying, intensively managed landscapes. This study employs an integrated Analytic Hierarchy Process (AHP) and Geographic Information System (GIS) approach to assess and map flood risk in the Wonji area of the Oromia Region, Ethiopia. Eight key geo-spatial and hydrological parameters such as rainfall, distance from stream, land use/land cover, population density, elevation, slope, drainage density, and soil type were selected based on literature and local context. Factor weights were derived via the AHP, with a satisfactory consistency ratio (CR = 0.088), revealing distance from stream as the most influential factor (weight = 0.459). The weighted factors were integrated using a Weighted Linear Combination (WLC) in a GIS environment to generate a Flood Risk Index (FRI). The resulting map was classified into five risk zones: Very low, low, moderate, high, and very high. The findings reveal that over 56% of the study area (265.82 km2) falls under high to very high flood risk, predominantly along major stream networks and in densely populated, low-lying zones. These areas correlate with agriculture, vertisol-dominated soils, irrigated sugarcane plantations, and settlements with high water tables. The findings underscore the acute vulnerability of the Wonji area driven by its anthropogenic modifications, and hydrological conditions. This study provides a scientifically robust and spatially explicit risk zonation map essential for designing flood mitigation measures such as early warning mechanisms, land use and settlement planning, and environmental resilience strategies to reduce flood vulnerability and risk in the Wonji area.