Estimativa e espacialização da erosividade no estado de Alagoas

Abstract

The lack of rainfall data in the state of Alagoas, similar in many regions of the country, makes use of the regression equations obtained in other regions of Brazil to calculate the R factor of the Universal Soil Loss Equation (USLE), which predicts the annual loss of soil in a given area. T o date, Alagoas does not have a study on rain erosivity. Therefore, the study aims to: i) define an equation to estimate rainfall erosivity based on the index EI30 and the rain coefficient ( Rc ), where E is the total kinetic energy of the rain and I30 is the maximum intensity of the rain in 30 minutes, and ii) characterize and spatialize erosivity in the state of Alagoas based on historical rainfall data. Rainfall data from 54 stations, over a 56-year period (1960 - 2016), were used to estimate erosivity, filling in the gaps via the imputation method (mtdsi package) in the R environment. The equation used showed consistency and significant correlation between the observed and estimated data, based on the coefficients of determination R2 (86%) and Pearson's correlation r (93%) and the lowest Square Root of the Mean Error - RMSE (775.2 MJ.mm.ha-1 . h- 1 ), which in turn indicated Ordinary Kriging (KO) as the best spatial interpolator. Based on the cluster analysis (AA), three homogeneous groups were identified due to intra-group similarity (G1, G2 and G3) of erosivity in the State, with the Complete method defined as the best from the Cophenetic Correlation Coefficient (CCC)> 0, 7. The G1 group is the smallest group formed, located in Eastern Alagoas. Groups G2 and G3 are the largest in extension and are located in the climatic mesoregions of Agreste and Sertão. The monthly isoerosivity showed that the highest rates occurred between April and July, with variations between 325.4 and 2.215.9 MJ.mm.ha-1 .h- 1. In annual erosivity, the most erosive locations were in Eastern Alagoas, close to the coast. Highlight for the stations Satuba (11,469.8 MJ.mm.ha-1 .h-1 .year-1), Maceió (9,945.4 MJ.mm.ha- 1 .h-1 year-1), São Luiz Quitunde (9,806.2 MJ.mm.ha-1 .h-1 .year-1) and Flexeiras (9,723.6 MJ.mm.ha-1 .h-1 .year-1), being categorized between moderate and strong. Therefore, the erosivity equation can be used to estimate the USLE R factor in the state of Alagoas. Regarding the use of precipitation products CHIRPS and CHELSA to estimate erosivity, both proved to be an alternative based on the statistical data found. Regarding the trends of rain and erosivity, the first showed a growth trend in the central region of the State, mainly in the Sertão Alagoano mesoregion, while the erosivity trend showed a greater growth close to the coast in the eastern Alagoan mesoregion. The results obtained in this study support the planning of conservationist practices, especially in vulnerable areas in Alagoas.