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.
