Groundwater recharge from heavy rainfall in the southwestern Lake Chad Basin: evidence from isotopic observations

Abstract

We examine groundwater recharge processes and their relationship to rainfall intensity in the semi-arid, southwestern Lake Chad Basin of Nigeria using a newly compiled database of stable isotope data (δ 2 H, δ 18 O) from groundwater and rainfall. δ 18 O signatures in groundwater proximate to surface waters are enriched in 18 O relative to regional rainfall and trace focused groundwater recharge from evaporated waters via ephemeral river discharge and Lake Chad; groundwater remote from river channels is comparatively depleted and associated with diffuse recharge, often via sand dunes. Stable isotope ratios of O and H (δ 2 H, δ 18 O) in groundwater samples regress to a value along the local meteoric waterline that is depleted relative to weighted mean composition of rainfall, consistent with rainfall exceeding the 60 th percentile of monthly precipitation intensity. The observed bias in groundwater recharge to heavy monthly rainfall suggests that the intensification of tropical rainfall under global warming favours groundwater recharge in this basin.

Water and Food Sustainability in the Riparian Countries of Lake Chad in Africa

“…Numerous factors have contributed to the conditions of Lake Chad, and one of the major contributors is the climatic conditions in the region. Indeed, it is seated in the Sahel, where there is scarcity and uneven distribution of rainfall [36], compounded with continuous drought prevalent in the region [29,37]. It is worth noting, however, that the recent observations depicted in Figures 2 and 3 suggest that there have not been significant changes in the patterns of rainfall and temperature.…”

Nitrate contamination of urban groundwater and heavy rainfall: Observations from Dakar, Senegal

“…In dryland areas of sub‐Saharan Africa, groundwater recharge occurs disproportionately from heavy, often extreme rainfall (Cuthbert et al., 2019; Goni et al., 2021; Seddon et al., 2021; Taylor et al., 2013). The mechanisms by which water surpluses from heavy rainfall events are transmitted to groundwater are often unclear but have been shown to include: (a) focused recharge via leakage from ephemeral streams or ponds (Favreau et al., 2009; Goni et al., 2021; Seddon et al., 2021), (b) rapid infiltration via macropores in low‐permeability weathered soils (Beven & Germann, 2013; Owor et al., 2009; Sorensen et al., 2021), and (c) permeable Quaternary sands (Cissé Faye et al., 2019; Goni et al., 2021; Kotchoni et al., 2019). Rapid responses in groundwater levels to heavy rainfalls observed from collated piezometric records in many of these cited studies have highlighted the vulnerability of groundwater to contamination.…”