Balanço de energia e evapotranspiraçâo em áreas com diferentes tipos de cobertura de solo no cariri cearense através do algoritmo SEBAL.

Abstract

The main objective ol'the present research was the assessment ol'the energy balance (lll-.) and daily evapotranspirneào (ii'l'), using “I'M — Landsat 5 images and meteorological data observed in the study area. 'i'he studied area comprises areas of microregion ofCariri, CE, cities ot“ Barbalha, Crato and Juazeiro do Norte, irrigated areas, native vegetation and Chapada do Araripe. Four images ot“ the TM m Landsat 5, obtained on September 29 (272), October 15 (288), October 31 (304) and November to (320), of the year ot'2005, were used. The instantaneons components ot'BE and daily ET were obtained according, to SEBAL (Surface Energy Balances Algorithnt for Land) proposed by Bastiaanssen ( 1995). The SEBAL is comprised by several steps, that include radiometric calibration, computation of the rellectivity and albedo, atmospheric correction of the albedo, vegetation indexes and emissivity for each individual pixel, based on tellective bands ol' TM - Landsat, and land surface temperature (thermal band). For obtaining Rn were used weather data in the studied area, in order to estimate global solar radiation and long wave atmospheric radiation. The main part OfSEBAL, however, is the determination of the sensible heat flux density (H), that is based on the concept ot'blending, height, logarithm the wind profile and correction i'or atmospheric stability, according to Monin-Obukhov similarity theory. The instantaneous Rn values presented averages ot'6149, 627.5, 651.5 and 620.5 Wmª, for the 272, 288, 304 and 320 days, respectively. The soil heat flux density (G), obtained as a Function of Rn, land surface temperature, albedo, IVDN and parameterization proposed by Bastiaanssen (2000), presented averages ol“99.9, 103.45, 100? and 103.6 Wm"2 on the 272, 288, 304 and 320 days, respectively. The density of flow of“ sensitive heat (H) it presented averages of181,3, 189,5, 217,1 and 161,9 Wmª on the 272, 288, 304 and 320, respectively. The talent heat llux density (LIE), calculated as residue of the energy balance equation, presented averages ol'334.2, 3350, 3338 and 363.1 Wmª, on the 272, 288, 304 and 320 days, respectively. The daily evapotranspiration (ET) presented averages of 3.8, 3.2, 4.6 and 3.4 mmday' ', For the 272, 288, 304 and 320 days, respectively. For validation of the results were considered data of two experimental and irrigated sites (with cotton and castor bean). The experimental and estimated data of Rn and LE presented ditl'erences within tºº/u, l'or three ofthe four analyzed days. The largest ditl'erences were verified for the H values, possibly influenced by the dimension of the experimental area and spatial resolution ot'the thermal channel.