Likely effects of land use changes on the runoff and aquifer recharge in a semiarid landscape using a hydrological model

A hydrological model for the estimation of the water balance components was developed for a semiarid landscape of Spain. These components were: the soil water content, the actual evapotranspiration ( E ta), and both the aquifer recharge (deep drainage) and runoff, which reflected water recharge, human use and soil erosion impacts. Combining the model predictions with the land cover vegetation units on the aquifer recharge area, created through a GIS (IDRISI), we compared the effects of some management policies on the deep drainage and runoff in five simulation scenarios. These scenarios included wildfires and vegetation management policies (afforestation and land abandonment). In order to implement the simulations, three precipitation levels were taken into account: mean annual rainfall in the area (300 mm), a wet year with 400 mm, and a very wet year (553 mm), where one of the rainfall events was an extreme rainfall event (153 mm), with a very high intensity. The results indicated that afforestation would produce a reduction of both the annual aquifer recharge and the runoff for the next 20 years and a wildfire would cause dramatic increases in the present aquifer recharge at current annual average precipitation. The results were not so marked if we took into account wet years and extreme rainfall events. Substantial variation occurred with the increased effect of wildfire on the risk of erosion at current annual average precipitation, but extreme precipitation during a wet year led to a higher erosion risk.