Important rainfall characteristics for soil and water conservation in Sao Manuel, State of Sao Paulo, Brazil

Mathematical models for soil erosion prediction are of unquestionable validity for planning the use of agricultural soils. The Universal Soil Loss Equation (USLE) is an example of such models and estimates the expected annual mean losses of soil in a given site and for a given management system based on the parameters: rain erosivity (R), soil erodibility (K), slope length (L), steepness (S), soil cover and management (C), and conservation practices (P). With the objective of contributing to conservation planning in the use of local soils, the rain erosivity factor (R) of the USLE was estimated in simplified form for a 49 year daily rain series in the county of Sao Manuel, Brazil (22 degrees 45 ' S latitude; 48 degrees 30 ' W longitude). Besides, the return period, frequency of occurrence of the annual rain erosivity indexes, and the maximum daily rain values for the calculation of canal dimension of agricultural level terraces were also calculated. The calculated value of parameter R was 7,487 MJ mm ha(-1) h(-1) year(-1), expected to occur at least once every 2.33 years at the site with a probability of 42.92%. A concentration of 81.48% of the total R value was observed from October through March, indicating that the greatest part of the annual erosion soil losses are expected to occur during this period. The values of the annual EI30 indexes for return periods of 2, 5, 10, 20, 50, and 100 years, were 7,216; 8,675, 9,641; 10,568; 11, 768 and 12,667 MJ mm ha(-1) h(-1) year(-1), respectively. Maximum daily rain quantities were 73, 98, 115, 131, 151 and 167 mm, respectively, for the same return periods.