Alterações no balanço radiativo e impactos climáticos decorrentes do uso da terra no Estado de São Paulo.

Abstract

When there is interest in determining the net radiation - Rn for heterogeneous areas the use of remote sensing techniques is very important. Rn is not usually measured in meteorological stations since it depends on the nature of the surface and thus is greatly influenced by albedo and land surface temperature. This study aims to evaluate whether changes introduced by land change use, particularly replacing the savanna (Cerrado) by sugar cane crop areas, can be detected through the use of MODIS sensor images onboard Terra satellite. Ten images referring to the sequential day of year 46, 52, 70, 89, 100, 102, 212, 228, 338 and 360 of 2005, covering the area of Santa Rita do Passa Quatro – SP municipality, were used. Therefore, three different methodologies - Bisht, METRIC and SEBAL - for calculating the instantaneous net radiation and its components were applied in order to determine the results. Data obtained from two icrometeorological towers located in Cerrado and sugar cane crop areas were used for validation and calibration of the models. The net radiation values in the savanna area were bigger than in the sugar cane crop area. The sugar cane area presented albedo and land surface temperature values bigger than those obtained in savanna areas. For the surface albedo was found an average percentage error of approximately 15%, for shortwave radiation of about 4%, about 5,5% for the atmosphere longwave radiation and 5% for the instantaneous net radiation. For the balance of radiation daily average error percentage was found around 10% and for the classical method, 14% for the classical model calibrated and 13% for the modified sinusoidal model. The techniques employed provide highlight patterns that distinguish the studied biomes and to conclude that replacement of Cerrado areas by sugar cane crop raise albedo and land surface temperature, and then impact locally the climate.