Observed controls on resilience of groundwater to climate variability in sub-Saharan Africa

Abstract

Groundwater in Africa supports livelihoods and poverty alleviation 1,2 , maintains vital ecosystems, and strongly influences terrestrial water and energy budgets 3. However, hydrologic processes governing groundwater recharge sustaining this resource, and their sensitivity to climatic variability, are poorly constrained 4,5. Here we show, through analysis of multi-decadal groundwater hydrographs across sub-Saharan Africa, how aridity controls the predominant recharge processes whereas local hydrogeology influences the type and sensitivity of precipitation-recharge relationships. Some humid locations show approximately linear precipitation-recharge relationships with small rainfall intensity exceedance thresholds governing recharge; others show surprisingly small variation in recharge across a wide range of annual precipitation. As aridity increases, precipitation thresholds governing initiation of recharge increase, recharge becomes more episodic, and focussed recharge via losses from ephemeral overland flows becomes increasingly dominant. Extreme annual recharge is commonly associated with intense rainfall and flooding events, themselves often driven by largescale climate controls. Intense precipitation, even during lower precipitation years, produces substantial recharge in some dry subtropical locations, challenging the 'high certainty' consensus that drying climatic trends will decrease water resources in such regions 4. The likely resilience of groundwater in many areas revealed by improved understanding of precipitation-recharge

The Lake Chad hydrology under current climate change

“…The water content of the subsurface can be separated in two components: the root zone soil moisture obtained from the Global Land Evaporation Amsterdam Model 25 (see supporting document for details of the GLEAM dataset), and the groundwater after removal of the root zone soil moisture from the subsurface storage. We estimate that Lake Chad's root zone soil moisture represents only 0.65 km 3 of the total annual amplitude, meaning that TWS variations are mostly driven by the changes in groundwater which is in agreement with groundwater data observations from Sahel 26 . Lake Chad's SWS and TWS exhibit similar time-variations (R = 0.81 over a 13-year period with one month of time lag).…”

The Impact of Land Use/Land Cover Change (LULCC) on Water Resources in a Tropical Catchment in Tanzania under Different Climate Change Scenarios

“…While climate change models show diverging trends of more dry or more wet conditions and changes in the seasonality, the impact of conversion from natural LULC into agricultural utilized fields is more explicit [3,4,81], although it still depends on the specific crops grown. Nevertheless, intensification of precipitation might foster groundwater recharge and therefore access to renewable water resources in the Kilombero Catchment as well as already described in other catchments in SSA [87]. This indicates a particular resilience to climate change and intensification of precipitation events.…”

“…This indicates a particular resilience to climate change and intensification of precipitation events. However, more observation-driven research is needed on the relation of surface water and groundwater resources on this topic [87]. Moreover, data availability on the hydrogeology of the Kilombero Catchment is still poor to be modeled precisely, although some data and a local conceptual model exists [88,89].…”

Drinking water quality from rural handpump-boreholes in Africa

“…Back et al 2018). The reasons for this are uncertain, but could be linked to more intense rainfall and/or flooding under wetter conditions (Bridgman et al 1995, Wu et al 2016 and the activation of rapid recharge pathways and/or shallower groundwater tables under wetter climate conditions (Gotkowitz et al 2016, Cuthbert et al 2019. It has been previously suggested that under wetter climatic conditions, microbiological contamination may be higher (Gotkowitz et al 2016), and with higher contamination during the wet season (e.g.…”

“…Understanding the quantity and accessibility of groundwater available for rural community supplies in Africa has been the primary focus of regional research to date (e.g. Macdonald et al 2012;Bonsor et al 2018, Cuthbert et al 2019. In contrast, the quality (both chemical and microbiological) of groundwater resources in Africa has tended to focus on areas with known natural water quality problems such as arsenic and fluoride (Reimann et al 2003, Edmunds and Smedley 2005, 2013, Rango et al 2013, contamination from mining (Smedley 1996, Von Der Heyden andNew 2004) or urbanisation (Lapworth et al 2017a).…”