Acessibilidade / Reportar erro

Rainfall Erosivity in the Municipality of São Pedro-SP: Analysis Between 1960-2020

Abstract

In São Pedro-SP, water erosion affects urban and rural areas and causes environmental, social, and economic losses. To understand the dynamics of erosive processes, it is essential to know the characteristics of the physical environment, including rainfall erosivity. In this context, the objective of this work was to characterize the rainfall erosivity in São Pedro, located in the state of São Paulo, using rainfall data of four temporal situations: 1960, 1972, 1988, 2010 and 2020. The analysis was developed based on the mean annual precipitation, rainfall erosivity index (EI30) and Rainfall Coefficient (R). For the spatial distribution of erosivity, the Inverse Distance Interpolation Power (IPD) was used in ArcGIS. The highest indices were observed in 1962 and 1972 and indicate that there was a reduction in erosive potential. The results allow to conclude that in São Pedro, there was rainfall with medium and high erosive potential, and it had a joint action with other environmental and anthropic factors, which could favor the deflagration and evolution of soil erosion. Therefore, these results are important and can help soil management and conservation planning, as well as the management of the territory, by following the characteristics of the physical environment.

Keywords:
Soil erosion; Erosivity; Interpolation

Resumo

No município de São Pedro - SP, a erosão hídrica afeta tanto a área urbana como a rural e acarreta perdas ambientais, sociais e econômicas. Para compreender a dinâmica dos processos erosivos é fundamental conhecer as características do meio físico, entre elas o potencial erosivo das chuvas. Nesse contexto, o objetivo deste trabalho foi caracterizar o potencial erosivo das chuvas no município de São Pedro, localizado na região centro-leste do estado de São Paulo, utilizando dados de chuva mensal para quatro cenários temporais: 1962, 1972, 1988, 2010 e 2020. A análise foi desenvolvida com base na precipitação média anual, Índice de Erosividade (EI30) e Coeficiente de Chuvas (R). Para representar espacialmente a erosividade foi utilizado o método de interpolação Inverso da Potência da Distância (IPD) em ambiente SIG (ArcGIS). Índices mais elevados foram observados nos anos de 1962 e 1972 e indicam que houve uma redução do potencial erosivo. Os resultados permitiram concluir que no município ocorreram chuvas com médio e alto potencial erosivo e, portanto, considerando sua ação conjunta com outros fatores ambientais e antrópicos, pode favorecer a deflagração e evolução das erosões. Além disso, esses resultados são importantes e podem auxiliar ações de manejo e conservação do solo, bem como a gestão do território, em conformidade com as características do meio físico.

Palavras-chave:
Erosão; Índice de erosividade; Interpolação;

INTRODUCTION

Rainfall erosion is one of the most common environmental degradations in wet regions, with strong damage to environmental resources and food production. It is related to two main factors: rain erosivity, which is related to rain intensity and time, and soil erodibility, which is due to the physical, mechanical, morphological, and usage conditions of soils (ZUQUETTE et al., 2007ZUQUETTE, L. V.; CARVALHO, A. R.; YAMANOUTH, G. R. B. Feicões erosivas na bacia do córrego Espraido, São Pedro (SP), seus tipos e evolução entre 1972-2002. Revista Brasileira de Geociências, v. 37, n. 2, 2007, p. 414-425. https://doi.org/10.25249/0375-7536.2007373414425
https://doi.org/10.25249/0375-7536.20073...
).

Thus, the understanding of erosive process dynamics and soil loss estimation requires knowledge of rainfall erosive potential. Rainfall erosivity is directly related to drop impacts on the soil and results from rain physical characteristics, such as quantity, intensity and maximum intensity (WISCHMEIER; SMITH, 1958WISCHMEIER, W. H.; SMITH, D. D. Rainfall energy and its relationships to soil loss. Transactions of the American Geophysical Union. v. 39, n. 2, p. 285-291, 1958, https://doi.org/10.1029/TR039i002p00285
https://doi.org/10.1029/TR039i002p00285...
; SANTA'ANNA NETO, 2011).

To measure this potential, Wischmeier and Smith (1958WISCHMEIER, W. H.; SMITH, D. D. Rainfall energy and its relationships to soil loss. Transactions of the American Geophysical Union. v. 39, n. 2, p. 285-291, 1958, https://doi.org/10.1029/TR039i002p00285
https://doi.org/10.1029/TR039i002p00285...
) proposed the erosivity index (EI30), indicated in the USLE (Universal Soil Loss Equation). EI30 represents the product between the kinetic energy and the maximum intensity of the rain and is based on the physical characteristics of the rain. However, according to Lombardi Neto and Moldenhauer (1992), the application of this index may present some limitations, especially in obtaining the maximum intensity and duration of rain, requiring detailed rainfall data analysis.

Considering this, several equations were developed for the indirect estimation of erosivity in Brazil, considering the relationship between the modified Fournier index, average monthly precipitation and average annual precipitation, and the EI30 index (OLIVEIRA; MEDINA, 1990; LOMBARDI NETO ; MOLDENHAUER, 1992LOMBARDI NETO, F.; MOLDENHAUER, W.C. Erosividade da chuva: sua distribuição e relação com as perdas de solo em Campinas (SP). Bragantia, Campinas, v. 51, p.189-196, 1992. https://doi.org/10.1590/S0006-87051992000200009
https://doi.org/10.1590/S0006-8705199200...
; RUFINO et al., 1993RUFINO, R. L.; BISCAIA, R. C. M.; MERTEN, G. H. Determinação do potencial erosivo da chuva do estado do Paraná, através de pluviometria: terceira aproximação. Revista Brasileira de Ciência do Solo, v.17, p.439-444, 1993.; GONÇALVES et al., 2006GONÇALVES, F.A.; SILVA, D.D.; PRUSKI, F.F.; CARVALHO, D.F.; CRUZ, E.S. Indices and spatialization of rainfall erosivity in Rio de Janeiro State, Brazil. Revista Brasileira de Engenharia Agrícola e Ambiental, v. 10, p. 269-276, 2006, https://doi.org/10.1590/S1415-43662006000200004
https://doi.org/10.1590/S1415-4366200600...
; HICKMANN et al., 2008HICKMANN, C.; ELTZ, F.L.F.; CASSOL, E.A.; COGO, C.M. Erosividade das chuvas em Uruguaiana, RS, determinada pelo índice EI30, com base no período de 1963 a 1991. Revista Brasileira de Ciência do Solo, v. 32, p. 825-831, 2008, https://doi.org/10.1590/S0100-06832008000200036
https://doi.org/10.1590/S0100-0683200800...
; CANTALICE et al., 2009CANTALICE, J. R.; BEZERRA, S. A.; FIGUEIRA, S. B.; INÁCIO, E. S.; SILVA, M. D. LINHAS ISOEROSIVAS DO ESTADO DE PERNAMBUCO - 1ª APROXIMAÇÃO. Caatinga, v. 22, p. 75-80, 2009.; SILVA et al., 2010SILVA, M.A.; SILVA, M.L.N.; CURI, N.; SANTOS, G. R.; MARQUES, J.J.G.S.M.; MENEZES, M.D.; LEITE, F.P., Evaluation and spatialization of rainfall erosivity in the Rio Doce Valley, central-eastern region of Minas Gerais, Brazil. Revista Brasileira de Ciência do Solo, v. 34, p. 1029-1039, 2010, https://doi.org/10.1590/S0100-06832010000400003
https://doi.org/10.1590/S0100-0683201000...
; ALMEIDA et al., 2011ALMEIDA, C.O.S.; AMORIN, R.S.S.; COUTO, E.G.; ELTZ, F.L.F.; BORGES, L.E.C., Erosive potential of rainfall in Cuiabá, MT: distribution and correlation with rainfall. Revista Brasileira de Engenharia Agrícola e Ambiental, v. 15, p. 178-184, 2011. https://doi.org/10.1590/S1415-43662011000200011
https://doi.org/10.1590/S1415-4366201100...
).

Specifically, in São Paulo State, several studies have developed this kind of equation, such as Carvalho et al. (1991CARVALHO, M. P. E.; LOMBARDI, NETO F.; VASQUES, J.; CATÂNEO, A. Correlação entre o índice de erosividade EI30 médio mensal e o coeficiente de chuva do município de Mococa, SP. Científica - Revista de Agronomia, v. 19, p.1-7, 1991.), Lombardi Neto and Moldenhauer (1992), Roque et al. (2001ROQUE, C.G.; CARVALHO, M.P.; PRADO, R.M. Rainfall erosivity factor at Piraju (SP), Brazil: distribution, probability of occurrence, return period and correlation with rainfall coefficient. Revista Brasileira de Ciência do Solo, v. 25, 147-156, 2001, https://doi.org/10.1590/S0100-06832001000100016
https://doi.org/10.1590/S0100-0683200100...
), Colodro et al. (2002COLODRO, G.; CARVALHO, M.P.; ROQUE, C.G.; PRADO, R.M. Erosividade da chuva: distribuição e correlação com a precipitação pluviométrica de Teodoro Sampaio (SP). Revista Brasileira de Ciência do Solo, v. 26, p. 809-818, 2002, https://doi.org/10.1590/S0100-06832002000300027
https://doi.org/10.1590/S0100-0683200200...
) and Silva et al. (2009SILVA, R.B.; IORI, P.; SILVA, F.A.M. Proposition and compare of equations to estimate the rainfall erosivity in two cities of São Paulo state. Irriga, v. 14, 533-547, 2009. https://doi.org/10.15809/irriga.2009v14n4p533-547
https://doi.org/10.15809/irriga.2009v14n...
). Among these, the equation developed with Campinas pluviometric data by Lombardi Neto and Moldenhauer (1992) stands out, since it shows excellent correlation between the rainfall coefficient and erosion index, allowing its application to other regions that do not have rainfall data.

After erosivity, it is possible to represent the spatial distribution of rainfall through maps using geographic information systems (GIS) and geostatistical tools (OLIVEIRA et al., 2012OLIVEIRA, P. T. S.; WENDLAND, E.; NEARING, M. A. Rainfall erosivity in Brazil: a review. Journal of Soil Science, v. 100, p.139-147, 2012. https://doi.org/10.1016/j.catena.2012.08.006
https://doi.org/10.1016/j.catena.2012.08...
; OLIVEIRA et al., 2015; TRINDADE et al., 2016TRINDADE, A.L.; OLIVEIRA, P. T. S.; ANACHE, J. A.; WENDLAND, E. Variabilidade espacial da erosividade das chuvas no Brasil. Pesquisa Agropecuária Brasileira. v. 51, p.1918-1928, 2016. https://doi.org/10.1590/s0100-204x2016001200002
https://doi.org/10.1590/s0100-204x201600...
; RICARDI, 2020RICARDI, A. M. Variabilidade espacial e temporal da erosividade das Chuvas (EI30) no estado de São Paulo, Brasil. 2020. Dissertação. Faculdade de Engenharia de Ilha Solteira, Universidade Estadual Paulista, Ilha Solteira, 2020.; SILVA NETO et al., 2020SILVA NETO, V. L.; BATISTA, E. D.; LEAL JUNIOR, W. B.; FABRIS, Z. V.; RODRIGUES, P. J. A. W. Distribuição espacial da erosividade das chuvas na bacia do rio Manuel Alves da Natividade, Tocantins. Sociedade & Natureza, v. 32, p. 161-175, 2020, https://doi.org/10.14393/SN-v32-2020-46182
https://doi.org/10.14393/SN-v32-2020-461...
). According to Oliveira et al. (2015OLIVEIRA, J. P. B.; CECÍLIO, R. A.; PRUSKI, F. F.; ZANETTI, S. S. Espacialização da erosividade das chuvas no Brasil a partir de séries sintéticas de precipitação, Revista Brasileira de Ciências Agrárias, v. 10, p.558-563, 2015, https://doi.org/10.5039/agraria.v10i4a4998
https://doi.org/10.5039/agraria.v10i4a49...
), interpolation methods such as weighted distance inverse (IPD) and ordinary kriking (KO) can be used to sucessfully determine the spatial distribution of erosivity. Interpolation using the IPD method estimates the values through the values of the nearest neighbor, weighted by the inverse of its distance raised to a power (CARUSO; QUARTA, 1998CARUSO, C.; QUARTA, F. Interpolation methods comparison. Computers Mathematical Application, v.35, n.12, p.109-126, 1998, https://doi.org/10.1016/S0898-1221(98)00101-1
https://doi.org/10.1016/S0898-1221(98)00...
). For Li and Heap (2008LI, J.; HEAP, A. D. A review of spatial interpolation methods for environmental scientists. Australian Government: Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia, 2008, 154 p.), Elbasti et al. (2013) and Oliveira et al. (2015), the IPD is a good method and is well suited to erosivity modeling. In addition, it is characterized by a fast and simple method and does not require many assumptions about the parameters of the model.

Considering this, the present work aimed to spatially characterize the erosive potential of rain in São Pedro (SP) using rainfall series from 1960 to 2020 as an important tool of natural environmental factors affecting linear erosion processes, as well as anthropic factors. Studies considering rain potential can provide important information, supporting diagnosis studies of erosive processes and the selection of erosion control and recovery measures.

METODOLOGICAL APPROACH

Study Area

The study area comprises the São Pedro municipality area, located in the central-eastern region of São Paulo State (Figure 1). The area is bounded by 183000 and 214000 E and 7480000 and 7517000 N UTM coordinates, Datum SIRGAS 2000 23S, covering an area of 611 km² with a population of 36,298 inhabitants.

The climate of São Pedro is Cwa (Köppen climate classification) and is characterized as mesothermic, with dry winters and hot summers (ALVARES et al., 2014ALVARES, A. C; STAPE J. L.; SENTELHAS P. C.; GONÇALVES, P. C.; LEONARDO, J.; SPAROVEK, G. Köppen’s climate classification map for Brazil. Meteorologische Zeitschrift, v. 22, p. 711-728, 2014. https://doi.org/10.1127/0941-2948/2013/0507
https://doi.org/10.1127/0941-2948/2013/0...
). The monthly average temperature oscillates between 16 and 27 ºC.

Figure 1
Location of the study area: São Pedro, São Paulo - Brazil.

Geological units include sandstones in the Botucatu, Piramboia and Bauru Formations, and basic intrusive rocks in the Serra Geral Formation (DUARTE, 1980DUARTE, U. Geologia ambiental da área de São Pedro - SP: vetor águas subterrâneas. 1980. 86p. Doutorado, Instituto de Geociências da Universidade de São Paulo, São Paulo, 1980.). The soils in the area were developed from these geological units, and most of them have a sandy texture. Sandy soils associated with Piramboia Formation sandstones, for example, are classified as susceptible to erosion (GOMES, 2002GOMES, D. M. Mapeamento geológico-geotécnico para análise de feições erosivas concentradas na Bacia do Córrego Ribeirão do Meio, região de São Pedro/SP, na escala 1:20.000. 2002. 242 f. Dissertação, Escola de Engenharia de São Carlos, Universidade de São Paulo, São Carlos, 2002.). Furthermore, geomorphological features and anthropic modifications contribute to erosive dynamics (MATHIAS, 2016MATHIAS, D. T. Contribuição metodológica para o diagnóstico da dinâmica erosiva linear e seu prognóstico evolutivo visando subsidiar projetos de recuperação. 2016. 178 p. Tese Faculdade de Ciências e Tecnologia, Universidade Estadual Paulista, 2016.).

In this context, in the municipality of São Pedro, erosion processes occur with different evolutionary stages, affecting both urban and rural areas (SANTORO, 1991SANTORO, J. Fenômenos erosivos acelerados na região de São Pedro-SP: Estudo da fenomenologia, com ênfase geotécnica. 1991. Dissertação. Instituto de Geociências e Ciências Exatas, Universidade Estadual Paulista, Rio Claro, 1991.; PEJON, 1992PEJON, O. J. Mapeamento geotécnico regional da folha de piracicaba - SP (Escala 1:100.000: estudo de aspectos metodológicos, de caracterização e de apresentação de atributos. 1992. Tese. Escola de Engenharia de São Carlos, Universidade de São Paulo, São Carlos, 1992.; GOMES, 2002GOMES, D. M. Mapeamento geológico-geotécnico para análise de feições erosivas concentradas na Bacia do Córrego Ribeirão do Meio, região de São Pedro/SP, na escala 1:20.000. 2002. 242 f. Dissertação, Escola de Engenharia de São Carlos, Universidade de São Paulo, São Carlos, 2002.; DANIEL, 2012DANIEL, E. Análise do papel da morfologia e do uso do solo na gênese e na distribuição de feições erosivas na Bacia do Córrego Espraiado, São Pedro - SP. 2012, 183 p. Dissertação. Faculdade de Filosofia, Letras e Ciências Humanas, Universidade de São Paulo, São Paulo, 2012.; IPT, 2012). Photographic records, maps and other literature data show the presence of erosion since 1960. Furthermore, according to the erosion map of the state of São Paulo, the municipality is located in a region with high susceptibility (KERTZMAN et al., 1995KERTZMAN, F. F.; OLIVEIRA, A. M. S.; SALOMÃO, F. X. T.; GOUVEIA, M. I. F. Mapa de erosão do estado de São Paulo. Revista do Instituto Geológico, p.31-36, 1995. https://doi.org/10.33958/revig.v16iesp.610
https://doi.org/10.33958/revig.v16iesp.6...
).

Erosivity Index (EI30) and Rain Coefficient (R)

To calculate the erosivity index, rainfall data from 1962, 1972, 1988, 2010 and 2020, available in the Department of Water and Electricity (DAEE, 2020) hydrological database, were used, rainfall stations located in the neighborhhod of the study area. Data from the Anhembi, Charqueada, Ipeúna, Itirapina, Piracicaba, Santa Maria da Serra and São Pedro rainfall stations were selected (Figure 2).

Figure 2
Location of the pluviometric stations.

To calculate the monthly rainfall erosivity (EI30), we used the equation proposed by Lombardi Neto and Moldenhauer (1992), as presented in Equation 1. The rainfall coefficient (R) was calculated from the sum of the EI30 values using Equation 2.

E I 30 = 68.73 ( p 2 / P ) 0.841 Equation 1

R = 1 12 E I 30 Equation 2

Where,

EI30 = average monthly rainfall erosivity (MJ.mm/ha.h.year);

= average monthly precipitation (mm);

P = average yearly precipitation (mm).

Finally, to prepare the erosivity maps, data were imported into ArcGIS and interpolated using the inverse weighted distance (IPD) method. The IPD method estimates the values based on the weighting of weights at each of the closest rainfall stations; that is, a function of the inversion of the distance power (ESRI, 2021), as described in Equation 3.

Z = i = 1 n 1 d i p z i i = 1 n 1 d i p Equation 3

Where,

Z = interpolated value;

n = number of observed data;

zi = values attributed to observed data;

di = distance between interplated and observed values.

As previously described, the IPD method choice was due to the good performance of this interpolator to obtain annual estimations of the erosivity index (LI; HEAP, 2008LI, J.; HEAP, A. D. A review of spatial interpolation methods for environmental scientists. Australian Government: Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia, 2008, 154 p.; ELBASTI et al., 2013; OLIVEIRA et al., 2015OLIVEIRA, J. P. B.; CECÍLIO, R. A.; PRUSKI, F. F.; ZANETTI, S. S. Espacialização da erosividade das chuvas no Brasil a partir de séries sintéticas de precipitação, Revista Brasileira de Ciências Agrárias, v. 10, p.558-563, 2015, https://doi.org/10.5039/agraria.v10i4a4998
https://doi.org/10.5039/agraria.v10i4a49...
; TEIXEIRA et al., 2021TEIXEIRA D. B. S.; CECÍLIO R. A.; OLIVEIRA, J. P. B.; ALMEIDA, L. T.; PIRES, G. F. Rainfall erosivity and erosivity density through rainfall synthetic series for São Paulo State, Brazil: Assessment, regionalization and modeling, International Soil and Water Conservation, 2021, https://doi.org/10.1590/S0100-204X2016001200002
https://doi.org/10.1590/S0100-204X201600...
). For annual erosivity spatial representation, two classification methods were considered: natural breaks and the classes proposed by Carvalho (2008CARVALHO, N. D. O. Hidrossedimentologia prática. Rio de Janeiro: Interciência, 2008.), adapted from Foster et al. (1981FOSTER, G.R.; MCCOOL, D.K.; RENARD, K.G.; MOLDENHAUER, W.C. Conversion of the universal soil loss equation to SI metric units. Journal of Soil and Water Conservation, v.36, p.355-359, 1981.). Thus, the first classification was adopted to assess the grouping of values intrinsic to erosivity data, and for comparative purposes with other maps, the classification proposed by Carvalho (2008) was also adopted, as shown in Table 1.

Table 1
Classes of annual erosivity factor (R).

RESULTS AND DISCUSSION

Data from rainfall stations located in the São Pedro region showed that the average annual rainfall for the period from 1962 to 2020 ranged from 1209 to 1572 mm/year (Figure 3). Comparing 1962, 1972, 1988, 2010 and 2020, the wettest year was 1962, with an average annual rainfall of 1572 mm/year; the least rainy year was 1988, with an annual average of 1209 mm/year. According to Perez-Filho et al. (2011), high rainfall, approximately 1400 mm/year, occurs abruply in the region due to the orographic effect of São Pedro ridges.

Considering only rainfall data from the São Pedro station (D4-060), the average monthly rainfall for the period from 1962 to 2000 was 183.7 mm in the wettest months and 54.7 mm in the driest months, as shown in Figure 4. The rainy season was concentrated between October and March, with an average monthly rainfall of 184 mm and the dry period occured between April and September, with a monthly average of less than 50 mm.

Figure 3
Annual average rainfall between 1962 and 2020 in São Pedro, São Paulo, Brazil.

Regarding erosivity, it is possible to observe greater values in December, January and February, with maximum values above 10,000 MJ mm ha-1 h-1 year-1 due to high rainfall. According to Carvalho (2008CARVALHO, N. D. O. Hidrossedimentologia prática. Rio de Janeiro: Interciência, 2008.) classification, these values characterize high erosive power rainfall. Furthermore, according to Perez-Filho et al. (2011), the rainy season contributes to the increase in rainfall intensity and, consequently, its erosive capacity. In this context, high-intensity rainfall can favor both the deflagration and the evolution of erosion in the region (DANTAS-FERREIRA, 2008DANTAS-FERREIRA, M. Proposta de índice para processos erosivos acelerados a partir de levantamento e diagnóstico geológico-geotécnico das áreas degradadas. 2008. 447 p. Tese, Escola de Engenharia de São Carlos, Universidade de São Paulo, São Carlos, 2008.).

Figure 4
Monthly average rainfall and erosivity between 1962 and 2020 for the pluviometric stations in São Pedro, São Paulo, Brazil.

Considering rainfall data from all stations in the region, the average annual erosivity index was 7,972 MJ mm ha-1 h-1 year-1 in 1960, 7,713 MJ mm ha-1 h-1 year-1 in 1972, 6,184 MJ mm ha-1 h-1 year-1 in 1988, 6,905 MJ mm ha-1 h-1 year-1 in 2010, and 6,977 mm ha-1 h-1 year-1 in 2020; as shown in Table 2. All values obtained represent rainfall with medium to high erosive potential.

Figure 5 shows the erosivity map of annual erosivity (R) using natural interval classification, allowing us to observe the temporal variation in annual erosivity in the considered years. In the region, rains with higher potential occurred in 1962 and 1972, and rains with lower potential occurred in 1988 and 2020. Thus, there was a reduction in the erosive potential of rainfall over the considered period. Regarding this variability, Mendonça and Danni-Oliveira (2011MENDONÇA, F., DANNI-OLIVEIRA, I. Climatologia: noções básicas e climas do Brasil. Oficina de Textos, São Paulo, 2011. 198p.) mentioned that the dynamism of the atmosphere and the successions of the climate reflect atmospheric instability, alternation of climatic times and the occurrence of precipitation.

Table 2
Rainfall erosivity for 1962, 1972, 1988, 2010, and 2020 in São Pedro town, São Paulo, Brazil.

The concentration of high erosivity values in 1972 (8,036 to 8,720 MJ mm ha-1 h-1 year-1) was possibly associated with the transition between the rainy and dry seasons. Ricardi (2020RICARDI, A. M. Variabilidade espacial e temporal da erosividade das Chuvas (EI30) no estado de São Paulo, Brasil. 2020. Dissertação. Faculdade de Engenharia de Ilha Solteira, Universidade Estadual Paulista, Ilha Solteira, 2020.), when characterizing erosivity in the state of São Paulo, also observed concentrations of this type in March, April, October and November for the 1997-2017 period. On the other hand, parallelism, observed mainly in the map of 2010, is related to the dynamics of air mass circulation, as well as the formation of cold and warm fronts. This fact was observed by other authors, when spatially representing the erosivity of rain in the state of São Paulo, such as Vieira and Lombardi Neto (1995) and Ricardi (2020).

Figure 5
Spatial distribution of rainfall erosivity in São Pedro, São Paulo, Brazil, for 1962, 1972, 1988, 2010 and 2020, considering the classification into natural intervals.

To support the analysis and interpretation of the erosive potential of rain, we adopted the classification proposed by Carvalho (2008CARVALHO, N. D. O. Hidrossedimentologia prática. Rio de Janeiro: Interciência, 2008.). The map presented in Figure 6 shows the classification in São Pedro in specific regions according to the erosivity classes. In all scenarios, rainfall was classified as having medium and high potential, with the exception of 1988, which was classified as having medium erosive potential.

Thus, rains usually classified as having high erosive power occurred in 1962 and 1972 in area in the municipality; that is, 92 and 61%, respectively (Table 3). For 1988, 2010 and 2020, most of the region was classified as having medium potential, with a percentage of occurrence above 90%.

Table 3
Interpretation classes of the annual erosivity factor (R).

The classification of annual erosivity obtained in this work converges with erosivity maps of the state of São Paulo prepared using the kriging method (RICARDI, 2020RICARDI, A. M. Variabilidade espacial e temporal da erosividade das Chuvas (EI30) no estado de São Paulo, Brasil. 2020. Dissertação. Faculdade de Engenharia de Ilha Solteira, Universidade Estadual Paulista, Ilha Solteira, 2020.). Considering the different temporal scenarios, the rains in the São Pedro region were classified as having medium and high erosive potential, characteristic of mountain areas. Furthermore, similar to the results obtained in this work, Ricardi (2020RICARDI, A. M. Variabilidade espacial e temporal da erosividade das Chuvas (EI30) no estado de São Paulo, Brasil. 2020. Dissertação. Faculdade de Engenharia de Ilha Solteira, Universidade Estadual Paulista, Ilha Solteira, 2020.) found reductions in the maximum erosivity value for the most recent periods.

Regarding the classification methods, the map in Figure 5, classified based on the natural interval method, allowed a better understanding of the distribution of erosivity values in the area. The natural interval metohd also allowed the identification of patterns (concentration of values and parallelism), similar to erosivity maps produced by other authors (VIEIRA; LOMBARDI NETO, 1995; RICARDI, 2020RICARDI, A. M. Variabilidade espacial e temporal da erosividade das Chuvas (EI30) no estado de São Paulo, Brasil. 2020. Dissertação. Faculdade de Engenharia de Ilha Solteira, Universidade Estadual Paulista, Ilha Solteira, 2020.).

Figure 6
Spatial distribution of rainfall erosivity in São Pedro, São Paulo, Brazil, for 1962, 1972, 1988, 2010 and 2020, considering the classification by Carvalho (2008CARVALHO, N. D. O. Hidrossedimentologia prática. Rio de Janeiro: Interciência, 2008.).

On the other hand, the map whose classification was based on Carvalho (2008CARVALHO, N. D. O. Hidrossedimentologia prática. Rio de Janeiro: Interciência, 2008.) adapted from Foster et al. (1981FOSTER, G.R.; MCCOOL, D.K.; RENARD, K.G.; MOLDENHAUER, W.C. Conversion of the universal soil loss equation to SI metric units. Journal of Soil and Water Conservation, v.36, p.355-359, 1981.) better reflects the potential of rainfall to cause erosion. This classification indicates that medium and high potential of rain can contribute to the deflagration and evolution of erosive processes in the area. Furthermore, in a region with relief and soils favoring erosion processes (GOMES, 2002GOMES, D. M. Mapeamento geológico-geotécnico para análise de feições erosivas concentradas na Bacia do Córrego Ribeirão do Meio, região de São Pedro/SP, na escala 1:20.000. 2002. 242 f. Dissertação, Escola de Engenharia de São Carlos, Universidade de São Paulo, São Carlos, 2002.), rains with high erosive potential can develop accelerated erosion features, such as gullies.

The characterization of rainfall erosivity in São Pedro showed that for the analyzed period, there were important changes in the temporal variability of rainfall potential against erosion. These changes may be associated with climate change and human action, at a regional and global levels, which in turn can modify the characteristics of rainfall (RICARDI, 2020RICARDI, A. M. Variabilidade espacial e temporal da erosividade das Chuvas (EI30) no estado de São Paulo, Brasil. 2020. Dissertação. Faculdade de Engenharia de Ilha Solteira, Universidade Estadual Paulista, Ilha Solteira, 2020.).

FINAL CONSIDERATIONS

The results show that the average annual precipitation for the region of São Pedro - SP was 1,334 mm/year. The analysis considering only the pluviometric station D4-060 confirmed the difference between rainy and dry periods, as well as its influence on erosivity. In this sense, periods with concentrations of rain, from December to February, increase the intensity of precipitation and, consequently, increase the erosive potential.

Regarding the annual rainfall erosivity (R factor) in the period from 1962 to 2020, the values obtained varied between 5,527 and 8,822 MJ mm ha-1 h-1 year-1. Therefore, in the municipality of São Pedro, rainfall with medium and high erosive potential occurs. There was also a reduction in the erosive potential; however, depending on the characteristics of the physical environment and land use, the rains that occur in the region can contribute both to the deflagration and acceleration of erosion processes.

The availability of long term consistent monthly rainfall data was very important and contributed to the understanding of the influence on erosive processes. The interpolation method returned good results and allowed the spatial representation of rainfall in São Pedro. In addition, the consideration of different time periods in the analysis was very useful for understanding the variability of rainfall over the years.

Thus, to complement the understanding of the potential of rain to cause erosion in São Pedro, it is recommended that new analyses be developed, considering other interpolation methods supported by geostatistics. Finally, the characterization of the potential of rain in the municipality of São Pedro for the period from 1960 to 2020 can support soil management and conservation practices in relation to agricultural use and can help the management of the territory, regarding the different forms of occupation.

ACKNOWLEDGMENTS

The authors thank the Instituto de Pesquisas Tecnológicas (IPT) and its foundation (FIPT) for their financial and institutional support through the “Novos Talentos”. This study was financed by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.

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Publication Dates

  • Publication in this collection
    12 Sept 2022
  • Date of issue
    2022

History

  • Received
    02 Feb 2022
  • Accepted
    17 Mar 2022
  • Published
    21 June 2022
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