Mecanismos biofísicos e características de controle da evapotranspiração da Caatinga em anos de seca extrema

Abstract

Seasonally Dry Tropical Forests (SDTF) are among the most important biomes regarding regional/global hydrological and carbon uxes. The Caatinga Biome is one of the largest STDF in the world that occupies a contiguous area of 844,453 km 2 , has a vast endemic biodiversity and is known an important wildlife area on the planet. Thus, the objective of this study was to evaluate the diurnal, seasonal and interannual variability of evapotranspiration (ET) and its biophysical control and characteristics (surface conductance - Gs; decoupling coe cient - Ω; e Priestley-Taylor coe cient - α) in a preserved Caatinga Biome environment during two dry years in the Brazilian northeastern region. A study on this subject with this level of detail in this biome is unprecedent. Measurements were carried out using an eddy covariance system during the period from 1st January 2014 to 31st December 2015. The lowest ET values were observed in the dry season of both experiment years (0.3 and 0.2 mm day-1) as a consequence of low soil moisture, which favored partial stomatal closure and reduced Gs values (0.22 and 0.13 mm s-1). The opposite occured in the wet season, when ET (2.6 and 1.7 mm day-1) and Gs (3.74 and 2.13 mm s-1) means reached higher values. Regarding annual values, di erences between total annual rainfall in both years is the most probable cause for the di erences observed in annual ET values. In 2014, ET was of 473.3 mm while in 2015 it was of 283.4 mm, which incurred in an overall decrease in Gs, Ω and α values. The results suggest that in the dry season, ET was controlled by soil moisture and, in the rainy season, it was partially controlled by available energy. With the present study, there was an advance in knowledge about the daily, seasonal and interannual variability of ET and its control characteristics. This information is bene cial, for example, in the calibration of models to make more realistic representations about the Caatinga Biome. As future perspectives, we intend to analyze the ET behavior in contrasting years and to evaluate soil moisture at multiple depths during an upcoming experimental campaign in the Caatinga Biome.