Land use change-driven streamflow fluctuations and implications for soil erosion modeling in Southern Brazil

The expansion of cropland has been demonstrated to be a significant disturbance to the environment, capable of altering hydrological processes, often resulting in modified streamflow characteristics and sediment fluxes. South America, especially Brazil, has undergone a significant - nearly double - increase in cropland since 2000, alongside temporally fluctuating land use and land cover (LULC) changes. However, the hydrological consequences of these changes continue to be a subject of debate in this region.

Here, we investigate the reciprocal effects of climate and LULC alterations on streamflow by conducting trend analysis and analyzing long-term time series data of streamflow and precipitation (i.e., 38 years of data provided by the National Water Agency (ANA) of Brazil) over 78 catchments. Additionally, we use the WaterSed model to simulate runoff and soil erosion in response to specific sequences of rainfall events occurring in the selected catchments.

A considerable and statistically significant increase has been observed in soybean croplands following a shift from other temporary crops (such as maize, wheat, oats, etc.), which was also associated with a statistically significant reduction of 34% in the catchment’s runoff coefficient. In contrast, we found that the annual trends related to rainfall and streamflow were statistically insignificant. A 27 % increase in water demand is also interpreted as an important proxy that is linked to the expansion of soybean croplands, supporting a decrease in the runoff coefficient. Consequently, we may primarily attribute these alterations to LULC changes. These outcomes will be used to calibrate a soil erosion model (WaterSed) to understand the impact of potential LULC changes on water and sediment fluxes in the future.