Flood susceptibility zoning in Botswana’s Notwane Urban Catchment: A triangulated and blended analytical hierarchy process-geographical information systems-based multi-criteria analysis

Abstract

Botswana’s economy is highly exposed to floods, estimated to cost an average of $90 million, about 0.56% of the total annual country gross domestic product. Flooding is common in urban catchments, including Botswana’s Notwane Catchment. The catchment is characterised by increased population anchored in the capital Gaborone, infrastructure expansion and altered natural drainage. The effects of floods necessitate proactive interventions that consider blended approaches for selecting, assessing and mapping flood conditioning factors (FCFs). This study aimed to demonstrate a triangulated, multicriteria approach for flood susceptibility mapping in the Notwane Catchment. The FCFs were identified through questionnaire surveys, key informant interviews and literature, and these included land-use, rainfall, elevation, flow accumulation, slope and soil type, among others. The analytical hierarchy process (AHP), supported by principal component analysis (PCA), was employed to derive the weights of factors using the Business Performance Management Singapore AHP tool in Microsoft Excel. Weighted factors were integrated into ESRI’s ArcMap 10.8 for spatial analysis and mapping. Cumulative rainfall (38.79%) emerged as the most critical factor, while altered land-use (21.35%), with statistically significant clustering of risk around built-up areas and water bodies (GiP-value = 0.062), was the second-largest contributor. Approximately 57.6% (5201.2 km²) of the catchment area is at moderate risk of flooding, covering Greater Gaborone, Mochudi, Ramotswa, and Kanye.
Contribution: Research and promotion of triangulated and blended approaches anchored on geospatial technologies to investigate flood susceptibility will influence targeted and site-specific risk-informed development in urban catchments while addressing Goal 11 of the 2030 Agenda for Sustainable Development.