Rainfall variability and groundwater availability for irrigation in Sub-Saharan Africa: evidence from the Niayes region of Senegal

Recent research on climate change, within the context of Sub-Saharan Africa, has shown the vulnerability of groundwater resources to climate change and variability. In Senegal, agriculture is among the most important users of groundwater resources, especially in the northern coastal area called ‘Niayes’ where farmers practice irrigated agriculture and use almost exclusively the quarternary sand aquifer for their irrigation needs during the dry season – which is the main growing period. However, in Senegal, irrigated agriculture, particularly that of horticultural crops, mostly grown in the Niayes, has attracted less research attention in terms of studies focused on climate change or variability, compared to staple-growing rainfed regions. In the Niayes region, farmers grow most of Senegal’s horticultural production. Combined with human use of water resources, climate variability may threaten future irrigation water availability in the area. This paper uses an integrated hydroeconomic model and a rainfall generator to evaluate the impact of rainfall variability on irrigation water availability and simulate its implications on producers’ responses and groundwater management policy measures. Results show that groundwater availability is diminishing over time, resulting in higher water table depth and smaller water withdrawals by farmers who will tend to decrease the area allocated to crops and favor the higher-valued crops. These trends are accelerated under a drier climate regime. A taxation policy to stabilize the aquifer would induce a reduction of the area under cultivation and have negative implications on revenues. Supply-side measures to enhance recharge may not be technically or financially feasible. This suggests that Senegal needs to develop groundwater management options that favor sustainable use of agricultural water resources without hindering national horticultural production