Soil is a natural resource that has been affected by human pressures beyond its renewal capacity. For this reason, large agricultural areas that were productive have been abandoned due to soil degradation, mainly caused by the erosion process. The objective of this study was to apply the Universal Soil Loss Equation to generate more recent estimates of soil loss rates for the state of São Paulo using a database with information from medium resolution (30 m). The results showed that many areas of the state have high (critical) levels of soil degradation due to the predominance of consolidated human activities, especially in growing sugarcane and pasture use. The average estimated rate of soil loss is 30 Mg ha -1 yr -1 and 59 % of the area of the state (except for water bodies and urban areas) had estimated rates above 12 Mg ha -1 yr -1 , considered as the average tolerance limit in the literature. The average rates of soil loss in areas with annual agricultural crops, semi-perennial agricultural crops (sugarcane), and permanent agricultural crops were 118, 78, and 38 Mg ha -1 yr -1 respectively. The state of São Paulo requires attention to conservation of soil resources, since most soils led to estimates beyond the tolerance limit.

ABSTRACT:The soil is a key component of the Earth System, and is currently under high pressure, due to the increasing global demands for food, energy and fiber. Moreover, the management of agricultural systems is often inadequate and ignores the agricultural suitability of lands, and particularly the vulnerability of soils. This paper demonstrates the application of the concept of the Soil Lifetime Index (SLtI) for the entire state of São Paulo, at a spatial resolution of 30 m. The SLtI methodology represents a tolerance criterion and a diagnostic tool to assess the level of soil degradation by water erosion, based on estimated soil loss rates and on an average soil renewal rate. Two approaches were applied to determine: i) the remaining time (years) until the solum (horizons A + B) is removed by water erosion to a critical depth of 1.0 m (original approach); ii) the remaining time (years) until the top 0.25 m of the nutrient-rich soil surface is removed by water erosion (new approach). Several areas in the state have reached a very critical soil depletion level, due to the predominance of consolidated agricultural activities, mainly of sugarcane and livestock production (as in the mesoregions of Ribeirão Preto, Bauru, Assis, Itapetininga and Araraquara). Only 35 % of the study area is in conserved state; 65 % of the study area is in the state of resource degradation, requiring intervention to diminish soil loss rates -and of this total, SLtI is zero in 1 and 0.25 % of the study area, respectively, for the original (critical depth of 1 m) and the new approach (0.25 m). It was estimated that at the current soil loss rates, within 100 years, 20,000 km 2 of the total area of the state of São Paulo (248,209 km 2 ) will have reached the critical depth of 1.0 m, and the top 0.25 m of the soil surface from an area of approximately 76,000 km 2 will have been completely removed if the current pace of resource exploitation is maintained.

To evaluate the individual and combined impacts of increasing greenhouse gases and deforestation on extreme precipitation events in the Amazon Basin, we carried out 4 numerical experiments with the regional Eta model forced from the initial and boundary conditions of the global HadGEM2-ES model: (1) control experiment (CTRL); (2) RCP8.5 scenario; (3) DEFOREST scenario; and (4) RCP8.5+DEFOREST scenario. To analyze changes in extreme rainy events associated with the increase in greenhouse gases, deforestation, and their combined effect, anomalies were calculated from the sensitivity and control experiments. In the RCP8.5 scenario, there was an increase in the maximum number of consecutive dry days (CDD), a reduction in the maximum number of consecutive wet days (CWD), a reduction in total annual precipitation (PRCPTOT), and an increase in the maximum precipitation accumulated in 5 consecutive days (RX5Day). The DEFOREST scenario evidenced an increased CDD, and a reduction in the other indices (CWD, PRCPTOT, and RX5Day). Furthermore, the RCP8.5+DEFOREST scenario exhibited an increased CDD, and a reduction in the other indices (CWD, PRCPTOT, and RX5Day), but with more intense increases and reductions than observed in the DEFOREST scenario. In general, towards the end of the 21st century, the 3 scenarios are projected to increase the drought period, mainly on the boundary between the Brazilian states of Amazonas and Pará.

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