Performance of the SEBAL algorithm in estimating flow in watersheds in the Brazilian Savanna

Abstract

Studies of the variables making up the radiation balanceare essential in climatology, mainly to understand the dynamics of the hydrologic cycle. Decreases in rainfall can be linked to changes in actual evapotranspiration values on the surface, since changes in land use modify the albedo, the vegetation index, and the surface temperature.. The objective of the present study was to evaluate the performance of the Surface Energy Balance Algorithm for Land algorithm in estimating the annual flow in watersheds located in the Brazilian savanna, considered as the simplified result of subtracting the values of rainfall from actual evapotranspiration. The algorithm allows estimation of flows for watersheds that do not have monitoring points, contributing to studies of water availability in large regions that are difficult to access. The results showed a correlation coefficient of 0.99 and a coefficient of determination of 0.99 between annual flows estimated according to categories of use and coverage of land and flows observed at fluviometric stations, with a performance of 99%, indicating the applicability of the model to estimate flows in areas without monitoring points. For the monthly flows estimated from information recorded by INMET automatic stations, there is a considerable effect of seasonality, with a record of negative values in the dry period. Despite this, the estimated flows showed a correlation of 0.80 with the observed values, with a performance of 89%. On average, flows in the studied watersheds account for 20% of total rainfall volume, which is an underestimate in comparison with values measured in the field, with an average error of -0.5898 m³/s/m².

Keywords:
Environmental modeling; Geotechnologies; Radiation balance; Evapotranspiration