Analysis of Climate Change Impact on the Availability of Water Re-Sources in the Niger River Basin, with Focus the Niger Inland Delta (Nid)

Abstract

The Niger river basin is characterized by hydro-climatic changes induced by land use and climate change that have significant impacts on local populations. The Niger Inland Delta (NID) wetland comprises a large flooded area that plays an important role in the ecosystem services. A significant fraction of the river flow is lost through evaporation and water use in the NID and the conditions are likely to change with increasing population and changing inflow conditions. In this study, we evaluate the recent hydro-climatic trends in the upper basin and Niger inland delta of the Niger River basin in order to assess the potential climate change. Trend of Niger inland delta pan-evaporation were also analyzed. An overall decrease of precipitation (1950-2010) and runoff (1950-2010); and an increase of temperature (1980-2010) and pan-evaporation (1970-2009), were observed. However, when a long study period is considered, all the trends are not statistically significant. In the same way, when IPCC standard period (1981-2010) is considered; all the climatic data show a significantly increas-ing trend in the NID except the evaporation whose trend is not significantly decreasing over the area. In this period, significant decreasing trends are found for mean annual discharge at a 0.05 significance level. A comprehensive understanding of the NID’s hydro-climatological functioning is therefore crucial for assessing the water resources in the basin under changing conditions in the future. This study focuses on a comprehensive understanding of the NID’s hydro-climatological functioning using water balance model approach to develop NIDWat. After a clear description of the water budget’s elements specific to the NID catchment, a spatial and temporal dynamics of the annual flood across the NID over the period 2000-2009 was performed using data from satellite QuickSCAT and its associated sensor SeaWinds. The estimated areas were used along with observed discharge and remotely-sensed climatic data to quantitatively evaluate each water balance component. The results indicate: (i) a clear spa-tiotemporal of the flooded areas varied between 25,000 km2 in wet periods and 2000 km2 in dry periods; (ii) an average evapotranspiration loss of 17.31 km3 (43% of the total inflow) was assessed in the catchment; (iii) precipitation’s contribution to the NID’s budget totals 5.16 km3 (12.8% of the total inflow); and (iv) the contribution of return flow from irrigated fields totals 1.8 km3 (4.5% of the total inflow, among which 1.2 km3 are from “Office du Niger”) to the flooded areas, refined the NID’s water balance estimates. The NIDWat model vii was validated against observed river discharge and water abstractions and shows a good per-formance. We then implemented the model as a module in a hydrological model to assess the water balance in the NID and the downstream water availability under changing condi-tions. We use a multi model approach using regional climate data from the CORDEX initia-tive. Results suggest, despite decreasing runoff, an increase in ET losses and changes in the temporal dynamics of flooding that impact water resources availability downstream. Knowledge gained on NID’s water balance analysis will be used to develop and calibrate hydrological models in the Niger Inland Delta of the basin.