One possible way to evaluate the influence of the climatic changes on the groundwater flow regime is the use of numerical models based on distributed parameters. This kind of models can be used to investigate the aquifers hydraulic behaviour and, additionally, after calibration and validation, to simulate the pollutant or heat transport associated to a vector flux field.
The existence of a numerical model, which was calibrated using the field data for the karstic aquifer of Escusa, also called Castelo de Vide, in the central part of Portugal (Fig. 26.1), created a possibility to evaluate the impacts of different climate change scenarios for this aquifer. The model using the finite element numerical technique has some new potentialities when compared with the most commonly used ones to simulate the groundwater flux in a very heterogeneous media, as it is the case of karstic systems. This model permits the simulation of fluid fluxes simultaneously in one-dimensional, bi-dimensional and tri-dimensional domains. This potential permits the simulation of the duality of flow processes in karstic environments, reflected in the processes of recharge (diffuse and concentrated infiltration), in the vector flux field inside the aquifer (quick in caves and conduits and slow in the rock mass) and, finally, in the occurrence of concentrated discharge (karstic springs) and diffuse discharges in contact with wetlands or with porous hydrogeo-logical unities connected with the karstic system .
Four different scenarios were analysed with respect to the influence of climatic changes on the aquifer discharge rates in the future. The climatic models used were based on different scenarios created by the Hadley Centre for Climate Prediction and Research, with predictions for 50 and 100 years, using global and regional models defined for the latitude of Portugal. The study was based on the 40 years of climatic measurements, with evaluation of monthly recharge rates to the aquifer. Then, the expected variation of the discharge rates to the main stream crossing this aquifer, the Sever River, depending mainly on its groundwater, was studied according the four different future scenarios, as well as the variation in groundwater discharge rates from the aquifer to the granitic rocks in contact with the aquifer in its northern part.
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