Impact of climate changes on groundwater levels and dependent ecosystems

Groundwater is naturally present below the ground level and is a fundamental resource which supports the activity of the surface-level ecosystems. In the semiarid region of Portugal the vegetation ecosystems have been adapted by developing root systems which enable them to access deep soil water to cope with recurring droughts. As a result of environmental changes linked to climate change, water availability in the soil is expected to decrease as consequence of temperature increment and decline in precipitation. These changes will cause a drop in the aquifer recharge and phreatic level with possible impacts on the groundwater-dependent ecosystems. Within this framework, the objective of the project is to estimate the impacts of climatic changes on the groundwater system present in the study area, which is characterized from the geotechnical, meteorological and hydrogeological points of view. To address the problem, a numerical model of the portion between ground level and the water table, referred to as the “vadose zone”, is obtained. The model acts as an investigation tool to estimate the ecosystem water balance and the water table fluctuations for different scenarios. A present scenario is modelled to understand the processes taking place in a soil vertical profile and the effects of vegetation and water table position on water dynamics. Model calibration is done using experimental data from tests performed on collected soil samples to find soil hydraulic properties, then adjusted using in-situ data. The model is used to simulate future conditions in a climate change scenario and to evaluate their impact on the overall water balance, making predictions about the evolution of the groundwater position. The results show a high dependency of the ecosystem on the soil water availability, meaning that significant impacts are expected in a climate change scenario. In this case, the model predicts a general decrease in water table level, of up to 8 m by year 2100.