Effects of land‐cover changes on the partitioning of surface energy and water fluxes in Amazonia using high‐resolution satellite imagery

Abstract

Spatial variability of surface energy and water fluxes at local scales is strongly controlled by soil and micrometeorological conditions. Thus, the accurate estimation of these fluxes from space at high spatial resolution has the potential to improve prediction of the impact of land-use changes on the local environment. In this study, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) data were used to examine the partitioning of surface energy and water fluxes over different landcover types in one wet year (2004) and one drought year (2005) in eastern Rondonia state, Brazil. The spatial variation of albedo, net radiation (Rn), soil (G) and sensible (H) heat fluxes, evapotranspiration (ET), and evaporative fraction (EF) were primarily related to the lower presence of forest (primary [PF] or secondary [SF]) in the western side of the Ji-Parana River in comparison with the eastern side, located within the Jaru Biological Reserve protected area. Water limitation in this part of Amazonia tends to affect anthropic (pasture [PA] and agriculture [AG]) ecosystems more than the natural land covers (PF and SF). We found statistically significant differences on the surface fluxes prior to and~1 year after the deforestation. Rn over forested areas is~10% greater in comparison with PA and AG. Deforestation and consequent transition to PA or AG increased the total energy (~200-400%) used to heat the soil subsurface and raise air temperatures. These differences in energy partitioning contributed to approximately three times higher ET over forested areas in comparison with nonforested areas. The conversion of PF to AG is likely to have a higher impact in the local climate in this part of Amazonia when compared with the change to PA and SF, respectively. These results illustrate the importance of conserving secondary forest areas in Amazonia.

Assessment of an Automated Calibration of the SEBAL Algorithm to Estimate Dry-Season Surface-Energy Partitioning in a Forest–Savanna Transition in Brazil

“…Our estimates of energy partition (sensible and latent heat) for different land uses are in accordance with Restrepo-Coupe et al [117], who showed that converted areas (forest to cropland and pasture) presented a different behavior with relative reductions in dry season ET, consistent with increasing water limitation due to loss of deep roots that can access soil water. They are also in agreement with Oliveira et al [118] and Dias et al [4], who conducted studies in the southwest (Ji-Paraná River basin) and southeast (Xingu River basin) Amazon on the conversion between forest vegetation and cropland and pasture, showing substantial changes on surface energy (H and LE) and water (ET) fluxes. Furthermore, changes in β reflect alterations on surface energy fluxes partitioning between H and LE.…”

Forests Mitigate Drought in an Agricultural Region of the Brazilian Amazon: Atmospheric Moisture Tracking to Identify Critical Source Areas

“…Amazonian droughts are triggered by ocean conditions: El Niño Southern Oscillation (ENSO) events were important in the droughts of 1982, 1987, 1997–1998, and 2015, while droughts in 2005 and 2010 were mainly caused by high sea surface temperature anomalies in the North Atlantic Ocean, which created a dipole that increased subsidence and decreased rainfall over the southern Amazon (Marengo et al., 2015; Zeng et al., 2008). Land surface conditions can either mitigate or exacerbate reduced moisture supply from the ocean: Forest and pasture systems both have deep roots that allow them to access moisture and maintain ET even during drought conditions (Hodnett et al., 1996b; Nepstad et al., 1994), thereby maintaining water supply to the atmosphere, though pastures are generally more sensitive to drought than forests (Oliviera et al., 2019), and a reduction in ET by pastures could exacerbate drought. While ocean conditions are important drivers of drought, the role of forest and nonforest cover in mitigating or exacerbating drought in agricultural areas of the Amazon have not been quantified.…”

Reframing tropical savannization: linking changes in canopy structure to energy balance alterations that impact climate

“…Investigations of the impact of forest structure gradients and change on albedo typically contrast forest with highly altered vegetation types canopies. For example, higher albedo is typically found in pasture, crops, and cleared lands, relative to forest, at least after initial post‐fire increases in absorptive charred materials subside (de Oliveira and Moraes 2013, de Oliveira et al 2016, 2019, Faria et al 2018). The albedo of regenerating secondary forest appears to converge toward mature forest values (low values, i.e., ~0.1); however, seasonal differences in albedo and net radiation appear linked to structure in these forests (de Oliveira and Moraes 2013, de Oliveira et al 2016, 2019).…”

“…For example, higher albedo is typically found in pasture, crops, and cleared lands, relative to forest, at least after initial post‐fire increases in absorptive charred materials subside (de Oliveira and Moraes 2013, de Oliveira et al 2016, 2019, Faria et al 2018). The albedo of regenerating secondary forest appears to converge toward mature forest values (low values, i.e., ~0.1); however, seasonal differences in albedo and net radiation appear linked to structure in these forests (de Oliveira and Moraes 2013, de Oliveira et al 2016, 2019). Foundational energy and materials flux network studies highlight large scale gradients in Amazon forest function, including variation in seasonal patterns and the roles of water vs. radiation limitation of photosynthesis and latent and sensible heat fluxes (da Rocha et al 2009, Restrepo‐Coupe et al 2013).…”

“…For example, in Brazil in 2019, there was a roughly 50% increase from the previous year in deforestation followed by extensive fires (Escobar 2019), with similar forest loss rates recently recorded for Amazônia in other countries such as Colombia and Bolivia (Kalamandeen et al 2018, Salazar et al 2018). These changes impact ecosystem processes at local, regional, and global scales, including increasing atmospheric greenhouse gases such as CO 2 , CO, CH 4 , and N 2 O (Gash et al 2004, Davidson et al 2012, de Oliveira et al 2019). Efforts to model the effects of climate change suggest that portions of Amazon forests are threatened with conversion into a savanna due to tree loss from deforestation, fire, and die‐offs associated with extreme climate conditions and drought (Brando et al 2008, 2019, Nepstad et al 2008, Phillips et al 2009, Aragão and Shimabukuro 2010, Allen et al 2015).…”