What if the deforestation stops: impact on water budget components in West Africa

The land cover degradation in the Anthropocene under a changing climate threat remains one of the significant concern for water resources preservation and planning. The reciprocal effects of land degradation and climate change is reported as a complex scenario with direct and indirect impact on land surface processes (IPCC, 2023). The purpose of this work is to simulate the water fluxes and states under the anthopogenic influence (control - CTRL) and natural evergreen (EBF) conditions using the hydrological model WRF-Hydro with NoahMP as the Land Surface Model (LSM). The change in the temporal and spatial patterns is evaluated in terms of the potential impact associated with preserving the natural land cover in WA. To achieve this, the offline mode of WRF-Hydro is forced with meteorological dataset from ERA5-land for the two land cover scenarios at ~11km spatial resolution between 2011 and 2023. The water budget outputs are post-processed with the R package “rwrfhydro” which computes the total precipitation partitioning into surface runoff, evaporation, and water storage in the surface and subsurface components. The water budget terms are analysed with Man-Kendall’s statistics and the difference between the two scenarios evaluated using multivariate techniques (Principal component analysis - PCA and Canonical correlation analysis - CCA), and Wavelet analysis.The results show that whatever the land cover scenario the leading temporal variations of the total precipitation (PC1) have a strong relationship with the water storage (groundwater, total soil moisture, and canopy water) while lags in the signals are more likely to have higher correlation with the surface and subsurface runoff. Further, the canonical loadings of the CCA modes of the water storage terms, evaporation terms and total precipitation indicate a shift towards the dry northern part (Sahel) of the study area. Compared to the CTRL simulation, the EBF scenario decreases the runoff fraction while increases the evaporation and storage change fractions. The natural land cover scenario simulated in this study provide considerable insight into the potential benefits of land reforestation actions in West Africa and offers opportunities for better decision making.