Hydrological Modelling for Water Balance Components and Flood Hazard Assessment under Climate Change in Mono, Lower Basin, Benin and Togo

Abstract

Climate change is expected to increase both the magnitude and frequency of extreme precipitation events, which may lead to more intense and frequent river flooding. This study evaluated the impact of climate change on water balance components and flood hazard in the Lower Mono river Basin through rainfall- runoff modelling. The projection from two West African Science Service Center on Climate Change and Adapted Land Use (WASCAL) climate model, GFDL-ESM2M and HadGEM2-ES under RCP 4.5 and the hydrological model HBV (Hydrologiska Byråns Vattenbalansavdelning) - light is considered in this study. HBV model was set up for the study area and the modelcalibration and validation was performed against the observed discharge measurments. Statistical bias correction (empirical quantile mapping) was applied to daily precipitation, temperature and evapotranspiration. Uncorrected and bias corrected climate data was then used as input for HBV model to simulate the water balance components. Considering both uncorrected and bias corrected climate variables, the projected climate change signal for the Basin was analyzed through the comparison between two future periods (2020- 2049 and 2070-2099) and the historical time period (1983- 2005). The impact of the detected climate change signal on flood frequency was then assessed using HYFRAN software. The results indicated that: (i) precipitation will increase by 19% and 35%; temperature increases from 0 to 1.17°C and 1.17 to 3.20°C; actual evapotranspiration increase by 9% and 20% and discharge increase by 59% and 102% respectively for the periods 2020-2049 and 2070- 2099 according to HadGEM2-ES model. GFDL-ESM2M model also illustrates an increase in precipitation by 15% and 30%, temperature from 0 to 6.5°C and 6.5°C to 7.41°C but a decrease in discharges by 58% for 2050 and by 44% for 2100 repectively. In case of impact of the climate change signal on flood frequency, the average change resulting from the two models indicated a decrease for the return periods 50, 20, 10, 5, 3 for future periods 2020-2049 and return period 50 for the period 2070-2099 whereas an increase for the return periods 3, 2 (2020-2049) and 20, 10, 10, 5, 3 and 2 (2070-2099).These results suggest for future flood management under climate change in Mono river basin to consider both increase and decrease in the flood frequency as the study shows that both trends are plausible