Agricultural demand and deforestation has transformed land use in Tropical South America in the last four decades. Changes in land use affect the hydrology of the region and can lead to a variety of hydrological and geomorphological changes. Previous studies (Costa et al. 2003 and Coe et al. 2009) have used models to correlate the increase in water discharge rate to deforestation of the area and climate variability. Coe et al. (2011) uses these methods to analyze discharge data and climate data in an 82,600 km2 basin of the Araguaia River in South America which is the center of agricultural and cattle production for the region. Discharge and precipitation data between two time periods (1970-1979 and 1990-1999) were used to compare low and high density land cover respectively. Two different simulations with different land cover (but identical climate forcing) were used. The first was IBIS-POT wand the second was IBIS-GRASS which represented undisturbed and disturbed land cover respectively.
Mean discharge for the basin increased by 25% between the two decades and the mean ratio of runoff to precipitation in each decade increased significantly by 4.8%. Although precipitation rate increased by 2.5% between the two investigated decades, this change was not enough to explain the increased discharge rate. This means that discharge increased between the two decades analyzed, but was not attributed to increased precipitation. Coe eta al. believe this change is a result of changed land cover because the climate data that was used to model the two-time period were exactly the same. This can be explained by the fact that changing the plants of the area often leads to increased discharge and soil erosion because water is not infiltrating the ground because agricultural crops often do not have the same root depth or density.
Coe, M. T., Latrubesse, E. M., Ferreira, M. E., & Amsler, M. L. (2011). The effects of deforestation and climate variability on the streamflow of the Araguaia River, Brazil. Biogeochemistry, 105(1-3), 119-131.
I have acted with honesty and integrity in producing this work and am unaware of anyone who has not. BP