Evapotranspiration Seasonality over Tropical Ecosystems in Mato Grosso, Brazil

Abstract

Brazilian tropical ecosystems in the state of Mato Grosso have experienced significant land use and cover changes during the past few decades due to deforestation and wildfire. These changes can directly affect the mass and energy exchange near the surface and, consequently, evapotranspiration (ET). Characterization of the seasonal patterns of ET can help in understanding how these tropical ecosystems function with a changing climate. The goal of this study was to characterize temporal (seasonal-to-decadal) and spatial patterns in ET over Mato Grosso using remotely sensed products. Ecosystems over areas with limited to no flux towers can be performed using remote sensing products such as NASA’s MOD16A2 ET (MOD16 ET). As the accuracy of this product in tropical ecosystems is unknown, a secondary objective of this study was to evaluate the ability of the MOD16 ET (ETMODIS) to appropriately represent the spatial and seasonal ET patterns in Mato Grosso, Brazil. Actual ET was measured (ETMeasured) using eight flux towers, three in the Amazon, three in the Cerrado, and two in the Pantanal of Mato Grosso. In general, the ETMODIS of all sites had no significant difference from ETMeasured during all analyzed periods, and ETMODIS had a significant moderate to strong correlation with the ETMeasured. The spatial variation of ET had some similarity to the climatology of Mato Grosso, with higher ET in the mid to southern parts of Mato Grosso (Cerrado and Pantanal) during the wet period compared to the dry period. The ET in the Amazon had three seasonal patterns, a higher and lower ET in the wet season compared to the dry season, and minimal to insignificant variation in ET during the wet and dry seasons. The wet season ET in Amazon decreased from the first and second decades, but the ET during the wet and dry season increased in Cerrado and Pantanal in the same period. This study highlights the importance of deepening the study of ET in the state of Mato Grosso due to the land cover and climate change.

Effect of urbanization on energy balance and evapotranspiration in an Amazon–Cerrado transition region in Brazil

“…The NDVI values of this study were close to those found in forest, grasses and buildup in Brazil 26 , 45 , 46 . A direct consequence of the reduction of vegetation cover is the change in the local microclimate, since vegetation plays an important role in maintaining climate balance, using solar radiation for the ET process and, consequently, decreasing the air and surface temperature 9 , 13 …”

“…This study was conducted during the region’s dry season to avoid the presence of clouds, which could make this study impossible, and to maximize the effect of forest replacement on SEB and ET. It is known that the Amazon-Cerrado transitional forest areas do not show great variation in LE and ET due to their high capacity to absorb water from the deep water table and maintain the ET rate even in drought conditions 8 , 13 . Thus, it was possible to observe that the decrease in native forest vegetation caused the distribution of available energy to change throughout the study.…”

“…It is known that the Amazon-Cerrado transitional forest areas do not show great variation in LE and ET due to their high capacity to absorb water from the deep water table and maintain the ET rate even in drought conditions. 8,13 Thus, it was possible to observe that the decrease in native forest vegetation caused the distribution of available energy to change throughout the study. The available energy was used to heat the air and the soil, mainly motivated by the reduction of surface humidity.…”

“…26,45,46 A direct consequence of the reduction of vegetation cover is the change in the local microclimate, since vegetation plays an important role in maintaining climate balance, using solar radiation for the ET process and, consequently, decreasing the air and surface temperature. 9,13 Areas with vegetation cover or dense vegetation have a high capacity to absorb incident shortwave radiation, i.e., they have low a sup , have greater soil water availability and, therefore, lower LST and lower longwave radiation emitted by the canopy vegetation. 9,47 Urbanized surfaces have a low vegetation density and a high rate of emission of polluting gases into the air, which increases the surface and air temperature.…”

“…The change in energy balance and surface ET patterns as a function of coverage change on a regional scale can be estimated using remote sensing techniques, given the wide spatial and temporal coverage of orbital sensors, good accuracy, and free image acquisition. 9,13,14 Among the most common algorithms for estimating energy balance and ET, the surface energy balance algorithm for land (SEBAL) has been applied in different types of surfaces, conditions and is economically viable due to use satellite imagery and some complementary surface data. 9,[15][16][17] Among the municipalities in the Amazon-Cerrado transition region that have grown the most in recent decades, Sinop has been a center providing services related to timber exploration and agricultural production since the 1980s.…”