Drought risk and climate change impacts on Querença-Silves aquifer and Odelouca watershed (Algarve)

Abstract

The evolution aquifer recharge and runoff in Querença-Silves aquifer and Odelouca watershed under three emissions scenarios (IS92a, SRES A2 e SRES B2), for year 2100, was calculated using BALSEQ daily water balance and a methodology developed by Oliveira et al. (2012) to generate the hydrological data required by this model. The results hint at a future drier climate regimes, with significant runoff reductions of 11 to 12% in Odelouca watershed and Querença-Silves aquifer while recharge decreases 17% in IS92a scenario; in SRES A2 (the most dry) recharge reductions in Querença-Silves are predicted to reach 54% and in Odelouca (dominated by low permeability formations) circa 63%; runoff reductions reach 67% (base runoff) in Odelouca and circa 50% in Querença-Silves. Drought risk analysis performed for Querença-Silves for today’s conditions, using precipitation data series for the past 30 years in São Bartolomeu de Messines, show that 10% of the years were very dry and 16.7% extremely dry, with extremely dry years having less than 394 mm/year precipitation. Comparing values between drought risk analysis with average precipitation and direct recharge for Querença-Silves show that in A2 scenario, average direct recharge is 136 mm/year, which is almost half of today’s and only slightly below today’s recharge for dry years (143 mm/year); in scenario IS92a (less dry) recharge (186 mm/year) is circa 83% of today’s. However, besides direct recharge and recharge due to irrigation losses, Querença-Silves also receives alochtonous recharge, which amounts to 16.7% of direct recharge. Bearing in mind that the above results of recharge and runoff will be the future “average” conditions, this means that for A2 scenario alochtonous recharge will suffer reductions of 50%. In any case and scenario, it seems that a dryer climate might be our future and the ensuing reductions in recharge and runoff will generate significant reductions in water availability, be it surface (dams) or groundwater. A very careful integrated management strategy will be required to ensure water supply and ecosystem preservation.