Current and Projected Climate Change Impacts over Inner Niger Delta Wetland of Mali

Abstract

This study aimed to evaluate the ability of selected RCMs and GCMs of CORDEX-CORE in reproducing the spatio-temporal patterns of some climatic variables, analyse the future climate scenarios over West Africa sub-region and assess the projected impact on changes in water density of the Inner Niger Delta (IND) wetland of Mali. A combinational metrics of three RCMs driven by three GCMs was used from 1970 to 2005 for evaluation. Three major climate variables, such as precipitation, air temperature, and evaporation, were evaluated using statistical parameters such as correlation coefficient (R), Mbias and RMSE compared to ERA5 data as observation. Results produced R values of 0.91 for the Sahel, 0.95 for the savannah, and 0.88 for the Guinea Coast for precipitation. Negative Mbias values reveal an underestimation of precipitation by the RCMs compared to ERA5. RMSE values range from 27.34mm to 151.53mm overall. For evaporation, R values are 0.93 for the Sahel, 0.93 for the savannah, and 0.86 for the Guinea Coast, with negative Mbias values except for CCLM5 simulations. RMSE varies from 9.54mm to 61.41mm overall. Air temperature R values are 0.86 for the Sahel, 0.93 for the savannah, and 0.93 for the Guinea Coast, with positive Mbias indicating that RCMs overestimate air temperature. Annual changes in precipitation, evaporation, air temperature, and runoff for West Africa were assessed under RCP 2.6 and RCP 8.5. RCP 2.6 shows moderate, regionally varied changes. Under RCP 8.5, precipitation and runoff decrease sharply, especially in the Sahel and coastal zones, while evaporation and temperature increase significantly, intensifying water stress across the region. Seasonal change in the precipitation, evaporation, air temperature and total runoff for the near and far future periods relative to the historical of the IND under RCP 8.5 and RCP 2.6 scenarios were then analysed. Precipitation shows high inter-model variability. Under RCP 8.5, the decrease is marked in MAM and JJA, with an increase in SON. Evaporation follows complex patterns across models. Temperature increases systematically. Runoff varies across seasons and models, which could affect water availability in the Inner Niger Delta (IND). SWAT hydrological model was used to assess the impacts of climate change on streamflow and runoff at three hydrometric stations of the IND with continuous and reliable data: Mopti, Diré and Tombouctou. The results showed a general increase in streamflow and runoff over the three stations studied. Under RCP2.6, increases were particularly pronounced in the months of September, October, November and December (SOND), reaching up to 90% in some localities. In contrast, under RCP8.5, although increases were still significant, they were more moderate and more concentrated in the wet season (JJA and MAM). These hydrological changes will have major implications for water availability, flood frequency, and water resource management in the Inner Niger Delta, while increased seasonal variability could impact the resilience of ecosystems and socio-economic activities dependent on the Niger River.