Evaluation of adaptation options to flood risk in a probabilistic framework

Study region City of Niamey, Niger, West Africa. Study focus This paper aims to explore the possibility of implementing a probabilistic framework for flood risk estimation for the city of Niamey, Niger. A probabilistic set of flood maps were generated by forcing a HEC-RAS model with a stochastically generated ensemble of flood peaks representing the river regime at Niamey. Loss curves were derived from expert judgment, and various adaptation options to flood risk were examined by considering two main variables: a) buildings’ material; b) dike height (ranged from 180.5 m to 184 m, at a 0.5 m interval) within a scenario-based framework. Floods with return periods of 2- to 1000-yr were considered in estimating total loss, and benefits and costs of different adaptation options were compared. New hydrological insights for the region It was found that increasing the height of the dikes would lead to smaller economic losses, while rebuilding with better materials would increase the average annual economic losses, but might decrease the risk of human casualties. Individual and combined impact of decision variables on flood risk were estimated for the city of Niamey. Quantitative tools were developed to help decision-makers and regulators choose the best preventive measures to mitigate flood risk.