Coupling MCDM-based ensemble and AHP for the sustainable management of erosion risk in a tropical Sub-Saharan basin

Intensified erosion threats are one of the major ecological problems ravaging global basins. To address this problem, it is crucial to identify erosion-prone areas at the sub-watershed level. In this study, a seven multi-criteria decision-making (MCDM) models ensemble was developed to prioritize sub-watersheds in the Anambra Basin based on erosion risk. The integration of the MCDM models with the Analytical Hierarchical Process and Geographic Information System with 23 geomorphometric parameters (specifically 12 linear, 6 shape, and 5 relief parameters), enabled a comprehensive ranking approach. The accuracy of the models was tested using normalised Spearman's rank correlation to compute a uniform sub-watershed ranking. The results revealed that the study area is a 7th order basin with drainage densities between 0.54 km/km² to 0.62 km/km², average peak flow between 88 m³/sec to 361 m³/sec, texture ratio between 2.54/km to 11.25/km, and mean basin slope values between 10.9° to 22.2°. Out of the eight sub-watersheds, as indicated by the MCDM models, H returned the highest aggregate rank (1st), making it the top priority for erosion risk mitigation while B ranked the least (8th) suggesting the presence of some environmental conditions that are less erosion prone. The top-ranked MCDM models, MOORA (multi-objective optimisation based on ratio analysis) and COPRAS (complex proportional assessment), show that they are the best options for managing erosion in the Anambra Basin. These findings offer prospects for sustainable erosion risk control at the sub-watershed level and a scientific basis for resource management for basins with similar characteristics around the world.