Assessing the Impacts of Climate Variability and Climate Change On Groundwater Recharge in Data-Scarce Tropical Basins

Groundwater recharge, a major limiting factor for the sustainable use of groundwater, can be affected by climate variability and by climate change. Although many aquifers and basins in tropical regions are being affected by these impacts, the limited climate and hydrogeologic data in those areas hinder application of groundwater models and the estimation of groundwater recharge under future scenarios. The objective of this work was to identify a suitable methodology for the estimation of the impacts of interannual climate variability and climate change on diffuse groundwater recharge in tropical basins where detailed climate and hydrogeological information is lacking. In order to illustrate the procedure, it was applied to the Femeas river basin, a tropical watershed in northeastern Brazil. Groundwater recharge in the period between 1977 and 2006 was estimated by an automated hydrograph recession-curve-displacement method, and the results compared well with those of other studies. Although yearly temperature and precipitation presented statistically significant increasing and decreasing trends in the period 1977-2006, respectively, groundwater recharge time series was considered stationary.  An empirical relationship obtained between observed monthly precipitation and monthly recharge was used to estimate groundwater recharge in future scenarios, using downscaled ETA GCM outputs. Though the expected reductions in the basin annual rainfall were 30% and 34% in 2080 (B2 and A2 scenarios, respectively), annual groundwater recharge would be reduced by only 7 and 8%. The possible explanation for this small sensitivity of groundwater recharge to reductions in annual precipitation in both actual and future conditions is that the intense storm events, responsible for effective groundwater recharge, would not be significantly affected by decreasing precipitation volumes.