Projections of climate and land use changes on water erosion in the Tocantins-Araguaia Basin

Abstract

The climate change scenarios, reported in recent studies, combined with the improper use and management of the soil, are an aggravating factor for the sustainability of agroecosystems. These facts tend to lead to the degradation of natural resources such as soil, water and forests, limiting the sustainable development of production systems. Among the aggravating factors, water erosion resulting from the possibility of increasing the erosive potential of rainfall and land use change is a relevant factor in studies involving future scenario changes. Therefore, modeling factors related to soil water erosion is essential, mainly in regions of Brazil with great agricultural and hydroelectric potential. The objective of this study was to evaluate the potential risk of water erosion under climate change in the Tocantins-Araguaia basin, the largest entirely Brazilian watershed, based on the rainfall erosivity factor - R factor of the Universal Soil Loss Equation (USLE). The R-factor was simulated for the condition of control of the near present climate and for future conditions from daily rainfall data obtained from a climate model ensemble in two climate change scenarios - RCP 4.5 and RCP 8.5. These scenarios originate from the fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) and are based on radiative forcing to simulate climate variables throughout the 21st century. In addition to the climate-related factor, the mapping of variables related to land use and land cover is of great importance for the analysis of changes arising from the expansion of agricultural activity within the Tocantins-Araguaia basin and its impact on climate change. In this context, future land use and land cover scenarios were predicted using cellular automata and Markov chain (CA-Markov) in two sub-basins, with the large industries for agriculture and cattle-raising prevailing in Tocantins-Araguaia basin. Working from a smaller scale of planning (sub-basin) to a large scale, the relationship between the potential risk of water erosion and the behavior of the NDVI was evaluated in a historical series in the Tocantins-Araguaia basin. The results showed how the expansion of pasture and agriculture areas based on their own patterns of change has been distributed in the sub-basin scale. This study revealed how future land use and land cover changes and water erosion predictions based on R-factor simulations interact in watersheds. The results reported here help research institutions, government, and farmers to act together facing climate change.