Spatial multi-criteria analysis for identifying suitable sites for integrated managed aquifer recharge and rooftop rainwater harvesting systems in Kumasi, Ghana

Abstract

Groundwater is essential for sustaining livelihoods and urban water security worldwide. In Kumasi, Ghana, rapid urbanisation, extensive impermeable surfaces, and significant population growth have substantially reduced natural groundwater recharge, presenting risks to long-term water security. To address this challenge, this study employs a novel GIS-based Multi-Criteria Decision Analysis (MCDA) framework that integrates managed aquifer recharge (MAR) with rooftop rainwater harvesting systems (RRWHS) to identify suitable recharge locations. Thirteen thematic criteria, including surface characteristics, hydro-socio infrastructural, and subsurface hydrogeological factors, were systematically evaluated using the Analytical Hierarchy Process (AHP). Suitability maps generated through weighted overlay analysis were validated using Monte Carlo, one-at-a-time (OAT) sensitivity analysis and the Receiver Operating Characteristic curve (ROC-AUC) methods. Results indicated that: (1) approximately 54.8 km² (27.2 %) of the Kumasi metropolis, mainly in the northern, northeastern and southern areas, is highly suitable due to favourable aquifer conditions (high transmissivity and hydraulic conductivity) and ample rooftop harvesting potential. (2) The study pinpoints conducive locations for the implementation of MAR-RRWHS to enhance groundwater recharge, particularly in impermeable urban settings. These findings provide strong, scientifically supported guidance for urban planners, water managers, and policymakers to effectively adopt MAR-RRWHS, promoting sustainable urban groundwater management in Kumasi and other rapidly urbanising areas worldwide.