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

The impacts of climate change on groundwater are poorly constrained, particularly in regions such as sub-Saharan Africa where global circulation models (GCMs) project different directions of precipitation change. Moreover, the timing of when climate change impacts on groundwater can be differentiated from natural variability has not been quantified. Here, for the first time, we estimate the time of emergence (ToE) of climate change impacts on groundwater levels, using time series from eight sites across Burkina Faso, West Africa. We apply output data from historical and RCP8.5 runs of CMIP5 GCMs to lumped groundwater models for each site, and estimate ToE by calculating signal to noise ratios for each site and CMIP5 model. We show that in addition to inconsistent direction of climate change impacts across different GCMs, there is inconsistency in the ToE of climate change signals in future groundwater levels, particularly in drying GCMs. Across the eight sites, between 5 (4) and 13 (13) CMIP5 GCMs of a possible 23 show a ToE associated with decreases (increases) in groundwater levels. ToE from CMIP5 GCMs producing decreases in groundwater levels (i.e. drying) is highly variable between sites and GCMs (across all sites, median ToE = 2049, interquartile range = 48 years). For CMIP5 GCMs producing increases in groundwater levels (i.e. wetting), ToE appears to occur earlier and with less variability (across all sites median ToE = 2011, interquartile range = 11 years). These results underline the need for development of no-regrets adaptation measures in parallel with reductions in GCM uncertainty

In-situ observations and lumped parameter model reconstructions reveal intra-annual to multi-decadal 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 multi-decadal (c. 1980s – 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 multi-decadal variability (five sites). We postulate that group 1 is controlled by anthropogenic influences (land use change and abstraction). Correlation of modelled water table depth and groundwater response times with hydrograph autocorrelation suggests that hydrogeological properties and structure control differences between group 2 and 3. Group 3 shows a small recovery in groundwater levels following the 1970/80s drought. Differences in intra-annual to multi-decadal 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

La gestion de l'eau et des infrastructures des petits perimetres irrigues

Sally, H. (Ed.), Ameliorer les performances des perimetres irrigues: Les actes du Seminaire Regional du Project Management de l'Irrigation au Burkina Faso, 24-26 Juillet 1996, Ouagadougou. Ouagadougou, Burkina Faso: IIMI. Burkina Fas