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

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.