Estimativa da evapotranspiraçao regional por meio de técnicas de sensoriamento remoto integradas a modelo de balanço de energia

Abstract

Este trabalho obteve estimativas da evapotranspiração regional a fim de acessar seu comportamento espacial. Foi utilizado o SEBAL (Surface Energy Balance Algorithm for Land) que tem como formulação básica o uso da equação do balanço de energia e a relação entre as radiâncias do espectro infravermelho termal e visível de áreas com contraste hidrológico suficientemente grande.

n this work regional evapotranspiration estimates are used to analyze spatial behavior. SEBAL (Surface Energy Balance Algorism for Land), whose basic formulation is the use of the energy balance equation and the relationship between visible and thermal infrared spectral radiances of areas with sufficiently large hydrological contrast, was used. From 44 AVHRR (Advanced Very High Resolution Radiometer) images obtained from NOAA-14 satellite, and also from ground station climatic data, actual ET cover series for Rio Grande do Sul State were generated, in 1998. Some representative areas of the State’s main cover classes were chosen. They presented, in decreasing order, the following annual mean losses (mm year-1): wetland (827), lake (732), forest (686), agricultural areas (458), grassland (453) and urban area (276). The classes with the least anthropic influence had the highest ET. An axis of ET decrease in the first half year from northwest to southeast, and, afterwards, an ET increase in the second half year, in the opposite direction was observed. The verifications were done by a simplified annual water balance over some hydrologic basins. Despite the uncertainties, the methodology is valid and has a great potential, since physical formulation allows access to ET spatial distribution.