Long-term increase in diffuse groundwater recharge following expansion of rainfed cultivation in the Sahel, West Africa

Abstract

International audienceRapid population growth in sub-Saharan West Africa and related cropland expansion were shown in some places to have increased focused recharge through ponds, raising the water table. To estimate changes in diffuse recharge, the water content and matric potential were monitored during 2009 and 2010, and modeling was performed using the Hydrus-1D code for two field sites in southwest Niger: (1) fallow land and (2) rainfed millet cropland. Monitoring results of the upper 10 m showed increased water content and matric potential to greater depth under rainfed cropland (> 2.5 m) than under fallow land (a parts per thousand currency sign1.0 m). Model simulations indicate that conversion from fallow land to rainfed cropland (1) increases vadose-zone water storage and (2) should increase drainage flux (similar to 25 mm year(-1)) at 10-m depth after a 30-60 year lag. Therefore, observed regional increases in groundwater storage may increasingly result from diffuse recharge, which could compensate, at least in part, groundwater withdrawal due to observed expansion in irrigated surfaces; and hence, contribute to mitigate food crises in the Sahel

Estimates of net infiltration in arid basins and potential impacts on recharge and solute flux due to land use and vegetation change

“…); it is not clear how important transition times for vegetation change are in the context of infiltration and recharge processes in the Trans-Pecos. The complex interactions between changes to vegetation and hydrological processes are a field of growing interest in arid/semi-arid regions (e.g., Bellot et al, 1999;Veatch et al, 2009;Gustafson et al, 2010;Royer et al, 2011;Ibrahim et al, 2014) and in wetter climates (e.g. Frankl and Schmeidl, 2000;Brown et al, 2005;Wilcox et al, 2006); incorporation of these processes into regional scale models may prove helpful in prediction of ecohydrological responses to disturbance and change moving forward.…”

Shallow groundwater recharge mechanism and apparent age in the Ndop plain, northwest Cameroon

“…The high recharge is probably enhanced by deforestation of the land for subsistence rainfed farming (Ibrahim et al 2014) that constitutes over 60 % of the land cover within the plain (Ndzeidze 2008). Similar high recharge rates have been reported in Uganda and Zambia (Taylor and Howard 1996 and references therein), and Ghana (Asomaning 1992;Yidana and Chegbeleh 2013) regardless of the varied methods used.…”

GRACE Detected Rise of Groundwater in the Sahelian Niger River Basin

“…The enlarged connectivity of surface runoff to underground aquifers generated increased focused groundwater recharge resulting in rising water tables even during droughts (Favreau et al, ). These counterintuitive phenomena are known as the “Sahelian paradox.” Furthermore, increases in diffuse groundwater recharge were explained by Ibrahim et al () as a response to expansion of agriculture in Nigerian Sahel. The rise in groundwater stocks continues until today (Favreau et al, , ; Ibrahim et al, ).…”