Balanços de radiação e energia em áreas de cultivo de cana-de-açúcar e cerrado no Estado de São Paulo mediante imagens orbitais.

Abstract

Remote sensing is a tool that make possible to identify important changes in several terrestrial biomes. The developed of new techniques in the last years has made possible the determination of the energy balance components with satellite images and few weather data. The research includes the basin of the river Mogi Guaçu because of changes in soil use to which it has undergone in recent decades and has attracted the interest of researchers to assess the impacts that these changes may promote the local climate. The present work has the main objective evaluate if the changes occurred in primary vegetation of Cerradão when this kind of vegetation is replaced by sugar-cane and eucalyptus crop, can be detected with SEBAL/METRIC. At the same time, if this algorithm can be applied and validated in the climatic conditions of Mogi – Guaçu basin. Eight TM - Landsat 5 images, in the orbit 220 and point 75, obtained in February 22, April 11, May 29, June 14, August 01 and 17, and November 21, 2005, were used with the SEBAL/METRIC algorithm. Radiometric calibration and spectral reflectivity for each TM - Landsat 5 band were determined. Then, an atmospheric correction was performed in order to obtain the surface albedo and thematic maps of the albedo, land surface temperature, vegetation indexes, net radiation, soil heat flux (G), sensible heat flux (H), latent heat flux (LE) and daily actual evapotranspiration (ET). The reference evapotranspiration was obtained with data from four weather stations: two micrometeorological (in Cerrado and in a sugar-cane) and two more located in São Simão and São Carlos cities, from the period of February 2005 to February 2006. The data from the two towers were used for validation and calibration of SEBAL/METRIC. The values of net radiation in the Cerrado, in general, were significantly larger than on the sugar-cane, mainly due to the largest albedo and temperature of this last one. In the wet period, the Cerrado presented evapotranspiration values (7.8 mm day-1) higher than the sugar-cane crop (6.3 mm day-1). The temperature on the Cerrado was usually smaller than on sugar-cane, in accordance with the partition of energy balance components along the year. The main conclusion is that the substitution of Cerrado for sugar-cane crop increases land surface temperature, air temperature, albedo and the sensible heat flux. On the other hand, it reduces the evapotranspiration and, therefore, the water mass flow for the atmosphere. The technique used makes possible to highlight patterns that differentiate the Cerrado from the other vegetation types of the Mogi - Guaçu river basin. The validation of some radiation and energy balance components confirm that SEBAL/METRIC can be used for evaluation of environmental impacts caused by change in primary vegetation in such climatic conditions of the study area.