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Title: Curve number estimation from Brazilian Cerrado rainfall and runoff data

item SANCHES OLIVEIRA, P. - Universidad De Sao Paulo
item Nearing, Mark
item HAWKINS, P. - University Of Arizona
item STONE, J. - Retired ARS Employee
item RODRIGUES, D.B.B. - Universidad De Sao Paulo
item PANACHUKI, E. - Federal University Of Rio Grande Do Sul
item WENDLAND, E. - Universidad De Sao Paulo

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2016
Publication Date: 9/6/2016
Citation: Sanches Oliveira, P., Nearing, M.A., Hawkins, P., Stone, J., Rodrigues, D., Panachuki, E., Wendland, E. 2016. Curve number estimation from Brazilian Cerrado rainfall and runoff data. Journal of Soil and Water Conservation. 71(5):420-429. doi:10.2489/jswc.71.5.420.

Interpretive Summary: Brazil has a large region of savannah, called the Cerrado, that is rich in biological diversity and freshwater resources. It is also being rapidly converted to agricultural use for production of both row crops and livestock. The Brazilian Cerrado is one of the most important Brazilian biomes, covering ~22% of the total area of Brazil. The vegetation of the Cerrado varies from grassland to savanna to forest. Because of its highly diverse plant and vertebrate species, this biome has been classified as one of the 25 global biodiversity hotspots. Despite the importance of the Brazilian Cerrado, knowledge of the hydrology associated with the change from native cover to grassland and cropland is still limited. In this study, we measured infiltration and runoff rates and amounts on plots with native Cerrado vegetation and the main crops found in the region. From the resulting data we derived widely used hydrologic modeling parameters, called curve numbers, that both help us to characterize the differences between the native and introduced vegetation and to model a part of the water cycle across wider area of the biome. We found that runoff was very different, and much greater, on the agricultural lands as compared to the native vegetation. In fact, we found that the Curve Number method was not suitable to estimate runoff under undisturbed Cerrado, bare coarse soils with high infiltration rates, pasture, and millet. These results are important for better understanding how to manage change in Brazil as more and more land is being converted to agricultural use.

Technical Abstract: The Curve Number (CN) method has been widely used to estimate runoff from rainfall events in Brazil, however, CN values for use in the Brazilian savanna (Cerrado) are poorly documented. In this study we used experimental plots to measure natural rainfall-driven rates of runoff under undisturbed Cerrado and under the main crops found in this biome, and derive associated CN values from the measured data using five different statistical methods. Curve numbers obtained from the standard table was suitable to estimate runoff for bare soil, soybeans, and sugarcane. However, CN values obtained from measured rainfall-runoff data (CN calibrated) provide better runoff estimates than the CN values from the standard table. The best CN values for the bare soil (hydrologic soil group B), soybeans, and sugarcane were 81.2 (78.5-83.9), 78.7 (75.9-81.5), and 70.2 (67.8-72.6). We concluded that the Curve Number method was not suitable to estimate runoff under undisturbed Cerrado, bare soil (hydrologic soil group A), pasture, and millet.