Climate Change Impacts in Soil-Water Balance in Semi-Arid Region, Southeast of Spain: The use of Eco-Hydrological Model

Predictions of climate change have a high interest in semiarid regions like the province of Alicante (SE Spain). It is expected that the decrease of precipitation and the increase of air temperature according to climate change forecasts, could impact on the recharge to aquifers. In this context, the aim of this study was explore the possible impact of climate changes forecasts on recharge in a small aquifer southeastern Spain. Air temperature and precipitation data in two climate change scenarios, B2-low and A2-high have been coupled to HYDROBAL model. The HYDROBAL software is a useful eco-hydrological model with daily resolution for assessing water balances in different vegetation types in a semiarid region of southeastern Spain. Based on two models, HYDROBAL and DISRUM, water balance was calculated on two scales (vegetation plots and watershed). Over the latter period (2071-2099), we expect reduced average annual groundwater recharge, of up to 17% (49 mm), if compared to the baseline period (1961-1990). Research Article


Introduction
Global climate change will produce a strong impact on the hydrologic cycle and therefore on water resources in many regions of the world, especially in semiarid regions, which seems to be a general agreement for academics and governments. The latest Assessment Reports of the Intergovernmental Panel on Climate Change [1], projects increase in precipitation on northern Europe indicate from 1-2% per decade, while in southern Europe shows a decrease up to 1% per decade (it may be up to 5% in summer). On the other hand, the frequency and duration of very wet periods have signifi cantly decreased in recent decades in many regions.
These general simulations have been specifi ed for Spain as it will be an increase of the mean annual temperature of 2.5 ºC and a decrease of the annual rainfall, range from 2 % in the basins of the North to 17% in the South basins. This study was carried out in the Ventós-Castellar aquifer ( Figure 1) located in the Municipality of Agost, Alicante Province, southeast Spain (38º 28'N, 0º 37'W). In this context, the aim of this study was assessing the impact of climate change forecasts on soil water balance and natural groundwater recharge in a semiarid area (SE, Spain) Air temperature and precipitation data in two climate change scenarios, B2-low and A2-high, were predicted using downscaled climate data from the HadCM3 Global Climate Model. These databases were coupled to a HYDROBAL hydrological model to determine the soil water balance and aquifer recharge.

Data processing
We selected regional projection precipitation and air temperature (maximum and minimum) data based on the   a General Linear Model univariate analysis was performed. Data were analysed by two-way ANOVA using two factors: (1) the period's factor (1961-1990, 2011-2040, 2041-2070 and 2071-2099) and (2) the emission scenarios factor (A2-high and B2-low). Annual precipitation (Figure 4a) and mean annual air temperature (maximum and minimum; Figure 4b) were used as the dependent variables.

Results
After applying the HYDROBAL model's water balance (Table   1)  and Jackson [5], indicated that the mean annual recharge rates will decrease by 14%. The same reduction value for the emission scenario A2-high (14%) has been reported by Pulido-Velazquez et al. [6], in the Serral-Salinas aquifer in Altiplano, Murcia, SE Spain, after applying different Regional Climate Models (RCMs).
The study area has a high potential vulnerability to climate changes. The changes projected in the precipitation and air temperature regime will signifi cantly infl uence the average annual recharge of the Ventós-Castellar aquifer. We will observe that during the last 2071-2099 period, the change in the percentage of aquifer recharge vs. the baseline period  will considerably decrease by up to 17% (49 mm).
This will imply a signifi cant reduction in the groundwater level, and will affect the main drinking water source of the town of Agost (5000 inhabitants).
The temporal variation analysis of the HYDROBAL model's output variables indicated a signifi cant decrease in water balance components (recharge, actual evapotranspiration, runoff and soil moisture; p < 0.01) with different amplitudes.
In both scenarios (A2-high and B2-low), a temporal decrease in the HYDROBAL model's output variables from the baseline period to the end of this century ( Figure 5).