Hydroclimatic variability and flood risk on Naglanou and Akissa forests areas in Mono River Delta (West Africa)

This study aims to analyze hydroclimatic variation (meaning rainfall and flow decrease or increase, regime irregularity, …) in Mono River basin and flood risk for ecological conservation of Naglanou (Benin) and Akissa (Togo) hydrosystems. Climate, hydrology and planimetry data were used for descriptive statistical and spatial interpolation to determine rain/flow relationship, climate balance (rainfall less potential evapotranspiration), flow coefficient (relationship between rainfall and flow), flood risk thresholds (base on Standardized Precipitation Index) return period. Naglanou and Akissa forest areas record heavy rainfall ranging 161 to 277 mm in June and 90 to 130 mm in October, representing respectively 16 and 13% of annual rainfall (1961-2015). This unequal spatiotemporal rainfall distribution determines surface flows and moisture of these forest sites during water level rise periods. Moreover, increase of flow rate by 20.38% over 1961-2015 and 14% over 1961-2000 linked to rainfall since 1990 and impoundment of Nangbeto dam since 1987. Flood hazard thresholds are limited (424.8 m3.s-1), moderate (609.3 m3.s-1), significant (709.1 m3.s-1), and critical (824.1 m3.s-1). Return periods correspond to 2, 10, 20 and 50 years.   Key words: Naglanou and Akissa Forest, biodiversity, mono River Delta, standardized precipitation index, flood risk threshold.