Determinação do fator de cobertura e dos coeficientes da MUSLE em microbacias no semiárido brasileiro

Abstract

as coberturas de Caatinga Nativa, Caatinga Raleada e Capim (pós desmatamento e queima) no semiárido brasileiro. Os dados foram coletados no período de 2009 a 2012. A avaliação dos ajustes do modelo foi realizada pelo coeficiente de Nash-Sutcliffe, índice de Willmott (id) e índice de confiança ou desempenho (c). Para determinação dos fatores C foram usados dados de parcela de erosão (20 m 2 ) empregandose 50% dos dados na calibração e os demais na validação. Já para calibração e validação dos coeficientes "a" e "b" da MUSLE, foram usados dados obtidos na escala de microbacia (1,15 a 2,8 ha). O maior valor do fator C foi registrado na Caatinga Nativa (0,0167), seguido pelo uso do Capim com 0,0084 e o menor valor para a Caatinga Raleada (0,0067). Os resultados indicam que os valores dos fatores C e os coeficientes de ajuste "a" e "b" da MUSLE, para as coberturas estudadas, se apresentaram apropriados e recomendados de acordo com os índices estatísticos empregados podendo ser utilizados como base para microbacias semelhantes não monitoradas.Determination of the cover factor and the MUSLE coefficients in watersheds in the Brazilian semiarid region A B S T R A C TThe aim of the present study was to calibrate and to validate the C factor of Universal Soil Loss Equation and the coefficients of the Modified Universal Soil Loss Equation for land covers of native 'Caatinga' , thinned 'Caatinga' and grass (after deforestation and burning) in Brazilian semiarid region. Data were collected in the period [2009][2010][2011][2012]. To evaluate the model performance, Nash-Sutcliffe statistical coefficient was determined, as well as the Willmott index (id) and confidence index (c). For determination of the C factor, data from erosion plots of a 20 m 2 were analysed, employing 50% for calibration and the other half for validation. For calibration and validation of the coefficients "a" and "b" of MUSLE, data obtained from watersheds (1.15 to 2.8 ha) were used. The largest value of C was recorded for native 'Caatinga' area (0.0167), followed by grass with 0.0084 and the lowest value of C (0.0067) was determined for the thinned 'Caatinga' . The results showed that the adjusted values of the C factor and the coefficients "a" and "b" of the MUSLE were appropriate and recommended according to the statistical analysis, and it can be used to simulate similar ungauged watersheds. Palavras-chave:perdas de solo erosão caatinga

Rainfall Characterization and Sedimentological Responses of Watersheds With Different Land Uses to Precipitation in the Semiarid Region of Brazil

“…The values obtained from the Equation 1 were used to calculate the erosivity index (EI30) (SANTOS et al, 2014) ), I30máx is the average maximum intensity of precipitation in thirty minutes (mm h -1 ) and P is the precipitation depth (mm).…”

Produtividade de fitomassa herbácea em diferentes manejos no semiárido cearense

“…O procedimento de ajuste de curvas de respostas para os diferentes tratamentos foi realizado através do software (SANTOS et al, 2014). Já o ano de 2013 registrou 12,5% abaixo da média histórica, com uma altura de 755,51 mm.…”

Sediment delivery ratio in a small semi-arid watershed under conditions of low connectivity

“…The Thornthwaite aridity index is 0.44, classified as semi-arid. Mean historical rainfall for the town of Iguatu is 864 ± 304 mm, of which 85% is concentrated in the period from January to May, and around 30% is recorded during March (SANTOS et al, 2014).…”

“…The class of soils with the greatest occurrence in the watershed was the Vertisols (45.63%); these soils are characteristic of expansive clays, with high rates of infiltration when dry (especially in the cracks), and low rates when wet. The map of soil and erodibility (K factor) ( Figure 1) was developed, based on published values from studies in the IEW (SANTOS et al, 2014), and from other works on the same types of soil in the watershed under study (RIBEIRO; ALVES, 2008).…”

“…To consider the effect of sediment deposition throughout its trajectory (BRACKEN;CROKE, 2007;FRYIRS et al, 2007), the concept of a Sediment Delivery Ratio (SDR) has been widely employed, defined as the fraction of gross erosion transported from a given area in a given time interval to the outflow of the watershed (LU et al, 2006). Studies, such as that of Santos et al (2014) who, studying small basins inserted in the Iguatu Experimental Watershed in the State of Ceará, calibrated and validated the C factor in the USLE and the energy term coefficients in the Modified Universal Soil Loss Equation (MUSLE), for ground cover of native caatinga, thinned caatinga and grass (Andropogon gayanus Kunt / after slash and burn) in the semi-arid region. However, studies of the Brazilian semi-arid region and, more precisely, of the Caatinga biome, which examine and quantify the actual sediment delivery ratio (SDR) are rare.…”