The Influence of Precipitation and Land Use Changes on Water Balance for a Plain Basin

The Argentine Pampas, one of the largest plains throughout the world, has experienced during the last 50 years a strong rise in the water table level, with the consequent increase in the frequency of floods. This dynamics is associated to two processes which developed over this zone. In the first place, the annual rainfall has shown a positive trend. Secondly, field crops have expanded throughout the Pampas, displacing grasslands and pastures, i.e., there has been a significant land use change.

Based on numerical simulations with a distributed in space, continuous in time, and properly calibrated and verified hydrological model, this paper shows that though the increase in rainfall is the prime phenomenon explaining the increase in groundwater levels, vegetation also plays a very significant role. Moreover, the non linear response of the hydrological system to changes in precipitation and land use is put into evidence, as the combination of both effects produces a result that is much less intense than the sum of each of the individual effects by themselves.

Additionally, the model indicates that there is an exponential relationship between the water table depth and the flooded areas, identifying a value of 2 meters for the water table depth as a threshold below which the flooded area grows significantly.