Erosão Hídrica na América do Sul: situação atual e projeções futuras

Abstract

Accelerated soil erosion is one of the most relevant natural processes in terms of environmental degradation, especially in tropical and subtropical regions, with implications for soil fertility, nutrient cycling, pollution of rivers and reservoirs, among other environmental impacts. In the humid tropics, the potential for water erosion increases due to the amount and intensity of rainfall, especially in areas with intense land use. The main erosive agent is rain, which has the ability to disintegrate soil particles, as well as transport sediments and nutrients. Therefore, this study aims to model soil water erosion in South America (S.A.) through the parameterization of the Revised Universal Soil Loss Equation (RUSLE) using available datasets, and to characterize the sediment delivery rate (SDR) for the basins of the continent, and, based on climate change projections, estimate it over the course of the present century. RUSLE is a model that combines the active factor (rainfall erosivity) and the passive factors (soil erodibility, slope length and slope, soil cover and conservationist practices). One of the most relevant applications of RUSLE is to predict the vulnerability of different regions to water erosion, enabling the mapping of average annual soil losses. To evaluate the SDR, the relationship between the modeling data that simulated the transport of sediments in 27 hydrographic basins of the S.A. with the water erosion of the soil of each basin was used. To estimate erosion throughout the 21st century, average annual precipitation data was used between 2010 and 2099 for S.A., obtained from the average of global climate models (GCMs-Ensemble) BESM, CanESM2, HadGEM2-ES and MIROC5, regionalized by the model Eta/CPTEC under the premises of the "Representative Concentration Pathway” (RCP's) 4.5 and 8.5. RUSLE performed satisfactorily for AS. The average soil loss was 3.8 t ha-1 year-1 . The highest soil losses were identified for Chile (>20.0 t ha1 year-1 ) and Colombia (8.1 t ha 1 year-1 ); Suriname, French Guiana and Guyana had the lowest values (< 1.0 t ha-1 year-1 ). The greatest soil losses were projected in the Andes Mountains and in the South-Central Region (SCR). In the first, the combination of “high” K factor, “very high” C factor and “very high” LS factor was the cause of the high soil loss values, being vulnerable to water erosion. In SCR, agriculture, livestock and deforestation were the causes of high soil loss as well as aggressive R-factor. The basins with the highest SDR values are in the Andes Mountains, due to the high sediment transport capacity, and in the Amazon River basin. The average potential erosion under the influence of climate change indicates an increase of 37%, reaching soil losses of the order of 5.2 t ha-1 year-1 over the 21st century for S.A. The projections indicate high soil losses for the region under the influence of the Andes Cordillera (SAR and CAR) and, for the SCR and SR (areas of agricultural and livestock use), less severe losses. For the northern region of S.A. (NAR, NER and NR), under the influence of native forest cover, projections show a reduction in water erosion by 2099. The impact of climate variation is projected more significantly for the last time slice (2071-2099), enhanced for RCP 8.5.