Abstract:
Water scarcity for smallholder farming in West Africa has led to the shift of cultivation
from uplands to inland valleys. This study investigates the impacts of climate and land use/land
cover (LULC) change on water resources in an intensively instrumented inland valley catchment
in Southwestern Burkina Faso. An ensemble of five regional climate models (RCMs) and two
climate scenarios (RCP 4.5 and RCP 8.5) was utilized to drive a physically-based hydrological model
WaSiM after calibration and validation. The impact of climate change was quantified by comparing
the projected period (2021–2050) and a reference period (1971–2000). The result showed a large
uncertainty in the future change of runoff between the RCMs. Three models projected an increase
in the total runoff from +12% to +95%, whereas two models predicted a decrease from 44% to
24%. Surface runoff was projected to show the highest relative change compared to the other
runoff components. The projected LULC 2019, 2025, and 2030 were estimated based on historical
LULC change (1990–2013) using the Land Change Modeler (LCM). A gradual conversion of savanna
to cropland was shown, with annual rates rom 1 to 3.3%. WaSiM was used to simulate a gradual
increase in runoff with time caused by this land use change. The combined climate and land use
change was estimated using LULC-2013 in the reference period and LULC-2030 as future land use.
The results suggest that land use change exacerbates the increase in total runoff. The increase in
runoff was found to be +158% compared to the reference period but only +52% without land use
change impacts. This stresses the fact that land use change impact is not negligible in this area, and
climate change impact assessments without land use change analysis might be misleading. The
results of this study can be used as input to water management models in order to derive strategies
to cope with present and future water scarcities for smallholder farming in the investigated area.
