Land Use and Climate Change Impacts on Water Resources and Water-Related Ecosystem Services Using a Multi-Model Approach in the Ouriyori Catchment (Benin)

Abstract

Predicting and supplying freshwater resources in West Africa remain major concerns and challenges, basically due to factors such as lack of operational governance frameworks, socio-economic factors, poor resources at political/decision-making levels, and scarcity of reliable hydro-meteorological observations and related factors. This study investigated the impacts of climate change and land use on water availability in the Ouriyori catchment. The catchment is a meso-based headwater catchment and covers an area of about 14.51 km2 of the sudanian north-eastern Volta basin of Benin. The annual growth rate of the population over the study area was about 2.54 % (2002-2013). First, land use/land cover (LULC) change was assessed using Landsat images over the period 1988-2016. Next, soil infiltration measurement was carried out over the catchment considering the major LULC (cropland and fallow) using the hood infiltrometer along the transect lines. Afterwards, based on field investigations and spatio-temporal LULC, field measurements on soil hydraulic properties and the daily climatic and hydrological observed data, two distributed and physically based hydrological models, the Water Simulation Model (WaSiM) and the Soil and Water Assessment Tool (SWAT) were successfully calibrated, validated and used to evaluate the catchment water balance for the study area. From the models’ outputs and demographic data, some Hydrological Ecosystem Services (HES) were assessed in line with the ecosystem accounting framework to identify changes in the capacity of the catchment to provide services such as crop water and household water supply. Finally, five climate model datasets of the Coordinated Regional Climate Downscaling Experiment project using the Representative Concentration Pathways 4.5, were used to analyze the projected climate change signal in the catchment. In addition, the climate models’ ensemble was applied in WaSiM and SWAT to determine the ability of the climate models to reproduce the catchment discharge. LULC in the catchment showed an increase in cropland of about 42 % and decreased inversely with natural vegetation. These changes were attributed to the population growth and the conversion of natural vegetation to agricultural land and the environmental conditions. The good performance between observed and simulated daily discharge of both models was indicated by the goodness of fit coefficients (R2, NSE and KGE) with values ranging between 0.75 and 0.89. Both models were found suitable for discharge modelling exercises. Added to that, the HES-service capacity was found to be in general higher than the HES-service flow for crop water supply, surface water supply (SW) and groundwater (GW) supply with a general annual decrease in service capacity of both SW and GW. Results of the climate signal indicated that rainfall will increase by about 3.5 % to 5 % for CNRM-CERFACS and ICHEC-HIRHAM whereas a decrease of 1.5 % to 3 % is shown by ICHEC-REMO, MPI-REMO and MPI-RCA. The mean temperature will increase by 2 ˚C under RCP4.5. However, the individual models showed a mixed trend in discharge change. In addition, due to the large associated uncertainty, the results of the ensemble RCMs-GCMs do not give a clear path of the future hydrological behavior. For the development of suitable adaptation strategies, a mixed trend may be considered. Despite these findings, this study has demonstrated that more appropriate strategies would have to be implemented for the adequate and sustainable management of land and water resources of the catchment.