Sociedade & Natureza ISSN: 1982-4513 Universidade Federal de Uberlândia, Instituto de Geografia, Programa de Pós-Graduação em Geografia Silva, Virgílio Loureço; Batista, Elismar Dias; Leal, Wilmar Borges; Fabris, Zanine Vargas; Rodrigues, Pedro James Almeida Wolney Spatial distribution of rainfall erosivity in the manuel alves da natividade river basin, state of tocantins, brazil Sociedade & Natureza, vol. 32, 2020, pp. 148-162 Universidade Federal de Uberlândia, Instituto de Geografia, Programa de Pós-Graduação em Geografia DOI: https://doi.org/10.14393/SN-v32-2020-46182 Available in: https://www.redalyc.org/articulo.oa?id=321364988011 How to cite Complete issue Scientific Information System Redalyc More information about this article Network of Scientific Journals from Latin America and the Caribbean, Spain and Journal's webpage in redalyc.org Portugal Project academic non-profit, developed under the open access initiative DOI: 10.14393/SN-v32-2020-46182 Received on: 01 December 2018 | Accepted on: 21 January 2020 Spatial distribution of rainfall erosivity in the manuel alves da natividade river basin, state of tocantins, brazil Virgílio Loureço Silva Neto1 Elismar Dias Batista2 Wilmar Borges Leal Junior3 Zanine Vargas Fabris4 Pedro James Almeida Wolney Rodrigues5 Keywords Abstract Hydrology. The objective of this work is to calculate the values of erosivity and Interpolation. map the monthly and annual rainfall erosivity in the Manuel Alves Soil loss. da Natividade river basin in the southeastern region of the state of Rainfall. Tocantins, Brazil, based on ordinary kriging (KO) interpolator and the performance evaluation of the spherical, exponential and Gaussian models using rainfall data for the period 1983-2013. Geostatistics was applied to map erosivity on both monthly and annual scales. The annual erosivity showed values between 8,332 and 9,253 MJ mm ha-1 h-1 year-1, with a peak in December, when it reached values of up to 2,170 MJ mm ha-1 h-1 year-1 per month. From May to September, erosivity presented values lower than critical, considered as 500 MJ mm ha-1 h-1 year-1 per month. Three critical regions were identified for planning actions aiming soil and water conservation: the northwest, the north and the central area of the Manuel Alves da Natividade river basin. INTRODUCTION irreversible damage to the soil and reduction in crop yields occur because of erosion, which is The erosivity index (EI) expresses the erosive why water erosion control programs are potential of rainfalls (WISCHMEIER, 1958). necessary for a stable agricultural practice. According to Hickmann et al. (2008), the According to Viola et al. (2014), the potential capacity of rainfalls to cause erosion knowledge of erosivity in space and time is can be defined as erosivity expressed through fundamental for the planning of soil and water this index. Also according to these authors, management and conservation practices that 1 Instituto Federal de Educação, Ciência e Tecnologia do Tocantins, Campus Gurupi, Tocantins. [email protected] 2 Instituto Federal de Educação, Ciência e Tecnologia do Tocantins, Campus Dianópolis, Tocantins. [email protected] 3 Instituto Federal de Educação, Ciência e Tecnologia do Tocantins, Campus Dianópolis, Tocantins. [email protected] 4 Instituto Federal de Educação, Ciência e Tecnologia do Tocantins, Campus Paraíso do Tocantins, Tocantins. [email protected] 5 Instituto Federal de Educação, Ciência e Tecnologia do Tocantins, Campus Dianópolis, Tocantins. [email protected] Soc. Nat. | Uberlândia, MG | v. 32 | p. 148-162 | 2020 | ISSN 1982-4513 148 SILVA NETO et al. Spatial distribution of rainfall erosivity aim to minimize the adverse effects of water rainfalls in Brazil using synthetic rainfall erosion. In this sense, the determination of the series. That work was carried out for the values of erosivity throughout the year allows national territory using data from 142 identifying the months on which the risks of pluviographic stations. For several regions of soil loss are the highest, which is why it plays Brazil, the erosive potential of rainfalls has an important role in planning conservation been extensively studied: Morais et al. (1991) practices based on soil maximum cover in for the southwest of Mato Grosso, Lombardi critical seasons of greater erosive capacity of Neto and Moldenhauer (1992) for the city of rainfalls (WISCHMEIER; SMITH, 1978; Campinas (state of São Paulo), Silva et al. BERTONI; LOMBARDI NETO, 1993). (1997) for the Goiânia region, Mello et al. (2007) The expansion of the agricultural frontier and Silva et al. (2010) for the state of Minas in the state of Tocantins, Brazil, reflects the Gerais, and Cassol et al. (2008) for São Borja in growing demand for agricultural commodities. Rio Grande do Sul state. With the continuous development of production At the international level, rainfall techniques, the state has been increasing its erosivity is an important object of study. Haas agricultural area. Thus, concerning soil et al. (2018), in studies carried out to model management and conservation, the type of crop climatic conditions and erosivity rates in the must be considered, but it is also of great northern Black Forest, Germany, stated that importance to understand the soil structure stable forest ecosystems are not prone to soil aiming productive efficiency, which involves loss. In addition, rainfall erosivity is low and the interpretation of data related to the practices that promote erosion, such as cuts, intensity and the frequency of rainfalls (SILVA are rare. However, from a climate change NETO et al., 2015). perspective, the authors claimed that an Silva (2004) stated that erosion maps can increase in extreme weather phenomena is be useful for environmentalists and expected. For example, in the southwest of agronomists to obtain knowledge about the Germany, the occurrence of strong storms erosivity potential of rainfalls in certain during the winter is expected. locations to implement the necessary Vrieling et al. (2010) claimed that, in precautions to minimize soil erosion in these Africa, human-induced soil erosion results from areas. an increasing pressure on natural resources, Studies on rain erosivity were developed leading to more intensive land use (for example, by Viola et al. (2014) for the state of Tocantins through land use changes), a reality that is and by Silva Neto (2015) for the city of similar as to what occurred in the Brazilian Taguatinga, in the southeastern region of the Cerrado after the expansion of the agricultural state. Considering the national scope, Oliveira frontier. et al. (2015) carried out studies with the Considering the importance of rainfall objective of spatializing the erosivity of erosivity regarding soil loss, especially in very Soc. Nat. | Uberlândia, MG | v. 32 | p. 148-162 | 2020 | ISSN 1982-4513 149 SILVA NETO et al. Spatial distribution of rainfall erosivity degraded areas with a high concentration of and an area of approximately 22,576 km2 rainfalls, the objective of this work is to (Figure 1). It is of great importance for the state calculate the values of erosivity and map the of Tocantins, as it is located within the Manuel monthly and annual rainfall erosivity in the Alves Project, in the southeast region, one of Manuel Alves da Natividade river basin in the the major irrigation projects in the country southeastern region of the state of Tocantins, because of the size of its water reservoir and the Brazil, based on ordinary kriging (KO) extension of the irrigable area by micro- interpolator and the performance evaluation of sprinkling, conventional dripping and the spherical, exponential and Gaussian sprinkling. Pineapple, banana, coconut, models using rainfall data for the period 1983- papaya, passion fruit and watermelon are 2013. cultivated there, in addition to cassava, corn, tomatoes, cabutiá pumpkin, sugar cane, guava, MATERIAL AND METHODS and peach palm (SEPLAN, 2012). The Manuel Alves da Natividade river basin belongs to the Tocantins River hydrographic system (right bank), with a drainage area of 14,934.93 km2 covering eleven municipalities Figure 1. Location of the Manuel Alves da Natividade river basin (A) and distribution of the stations used to map rainfall erosivity in ASTER digital elevation model (B). Source: Adapted from INPE, 2016. Org.: Author, 2018. Soc. Nat. | Uberlândia, MG | v. 32 | p. 148-162 | 2020 | ISSN 1982-4513 150 SILVA NETO et al. Spatial distribution of rainfall erosivity According to Souza (2019), there are selected in the area of the basin and its three homogeneous climatic regions in the state surroundings, thus obtaining historical series of Tocantins (Figure 2), namely a) the climatic with monitoring in an average period of thirty region C1s2A'a': dry sub-humid climate, with a years (between 1983 and 2013). high concentration of rainfalls in the summer, To calculate the erosivity of rainfalls in a megathermic; b) climate region C2wA'a': sub- location, it is recommended that the average humid climate, with a moderate water value of the erosion index be estimated for a deficiency in the winter, megathermic; and c) period of at least twenty years (HICKMANN et climate region B1wA'a': humid climate, with a al., 2008). The Wischmeier and Smith (1958) moderate water deficiency in the winter, equation, which is considered a reference for megathermic. The Manuel Alves river basin these studies, tends to underestimate the area comprises the C2wA'a' climate region. erosivity of rainfalls in tropical regions. The rainfall erosivity, called Factor “R” or Figure 2. Climatic classification of Thornthwaite EI30 erosivity index, numerically represents and Matter for the state of Tocantins the erosive force in MJ mm ha-1 h-1 year-1 as a unit of measurement; it is obtained by the multiplying kinetic energy (KE), expressing the rainfall hitting the ground, by the maximum intensity verified in 30 minutes, according to Equation 1. 퐸30 = 퐸푐. 퐼30푚푛 (1) The explanatory variable for calculating the index EI30 was the Fournier index (Rc).