In Situ Observations and Lumped Parameter Model Reconstructions Reveal Intra‐Annual to Multidecadal Variability in Groundwater Levels in Sub‐Saharan Africa

Abstract

Understanding temporal variability in groundwater levels is essential for water resources management. In sub-Saharan Africa, groundwater level dynamics are poorly constrained due to limited long-term observations. Here, we present the first published analysis of temporal variability in groundwater levels at the national scale in sub-Saharan Africa, using 12 multidecadal (ca. 1980s to present) groundwater level hydrographs in Burkina Faso. For each hydrograph, we developed lumped parameter models which achieved acceptable calibrations (NSE = 0.5-0.99). For eight sites not showing significant (p < 0.001) long-term groundwater level declines, we reconstructed groundwater levels to 1902, over 50 years before the earliest observations in the tropics. We standardized and clustered the eight reconstructed hydrographs to compare responses across the sites. Overall, the 12 hydrographs were categorized into three groups, which are dominated by (1) long-term declines (four sites), (2) short-term intra-annual variability (three sites), and (3) long-term multidecadal variability (five sites). We postulate that group 1 is controlled by anthropogenic influences (land use change and abstraction). Correlation of modeled water table depth and groundwater response times with hydrograph autocorrelation suggests that hydrogeological properties and structure control differences between groups 2 and 3. Group 3 shows a small recovery in groundwater levels following the 1970/1980s drought. Differences in intra-annual to multidecadal variability in groundwater levels have implications for water management and highlight the value of long-term monitoring. Reconstructions contextualize current groundwater status, forecasts, and projections. The approach developed is generic and applicable where long-term groundwater level data exist.

Linkages between GRACE water storage, hydrologic extremes, and climate teleconnections in major African aquifers

“…Expansion of the limited GW level monitoring data that are reported by the International Groundwater Resources Assessment Centre (IGRAC) would help with understanding the dynamics of GW storage in Africa (figure S16). Groundwater level monitoring is clustered in certain countries, such as South Africa [64], Burkina Faso [65], and Uganda [66]. Previous regional-scale studies have evaluated representative long-term GW level hydrographs [67].…”

Towards a historical precipitation database for West Africa: Overview, quality control and harmonization

“…WASCAL ON is a joint collaboration between the West African NHMS, WASCAL and partner institutions to strengthen the observational infrastructure of the West African NHMS and to improve the availability of hydro‐meteorological observations for this region (Salack et al ., 2019). Subsets of the WAHPD and related data products were already used by various investigations, for example, for evaluation of regional climate model simulations (Dieng et al ., 2017) and seasonal forecasts products (Bliefernicht et al ., 2019), analysis of precipitation extremes and comparison with satellite products (Engel et al ., 2017), as input information for groundwater reconstruction (Ascott et al ., 2020) and as climate background data of the WASCAL hydro‐meteorological observatories (Bliefernicht et al ., 2018; Salack et al ., 2018b; Berger et al ., 2019).…”

Time of emergence of impacts of climate change on groundwater levels in sub-Saharan Africa

“…We hypothesize that in addition to the variability in the direction of climate change impacts on groundwater levels from GCMs, different GCMs show significant variability in the ToE of climate change signals. We address this hypothesis by applying transient climate data from the CMIP5 ensemble to eight lumped conceptual groundwater models across Burkina Faso developed by Ascott et al (2020b), and consider implications for management of groundwater resources in the SSA context.…”