ENSO effects on the relationship between aerosols and evapotranspiration in the south of the Amazon biome.

The effects of the El Nino-Southern Oscillation (ENSO) events have local, regional, and global consequences for water regimes, causing floods or extreme drought events. Tropical forests are strongly affected by ENSO, and in the case of the Amazon, its territorial extension allows for a wide variation of these effects. The prolongation of drought events in the Amazon basin contributes to an increase in gas and aerosol particle emissions mainly caused by biomass burning, which in turn alter radiative fluxes and evapotranspiration rates, cyclically interfering with the hydrological regime. The ENSO effects on the interactions between aerosol particles and evapotranspiration is a critical aspect to be systematically investigated. Therefore, this study aimed to evaluate the ENSO effect on a site located on the southern portion of the Amazonian region. In addition to quantifying and testing possible differences between aerosols and evapotranspiration under different ENSO classes (El Niño, La Niña and Neutrality), this study also evaluated possible variations in evapotranspiration as a function of the aerosol load. A highly significant difference was found for air temperature, relative humidity and aerosol load between the El Niño and La Niña classes. For evapotranspiration, significant differences were found for the El Niño and La Niña classes and for El Niño and Neutrality classes. Under the Neutrality class, the aerosol load correlated significantly with evapotranspiration, explaining 20% of the phenomenon. Under the El Niño and La Niña classes, no significant linear correlation was found between aerosol load and evapotranspiration. However, the results showed that for the total data set, there is a positive and significant correlation between aerosol and evapotranspiration. It increases with a quadratic fit, i.e., the aerosol favors evapotranspiration rates up to a certain concentration threshold. The results obtained in this study can help to understand the effects of ENSO events on atmospheric conditions in the southern Amazon basin, in addition to elucidating the role of aerosols in feedback to the water cycle in the region.

Improvement of thermal comfort indices in agroforestry systems in the southern Brazilian Amazon.

Agroforestry systems can minimize heat stress and improve cattle welfare, but the influence of the forest component in microclimatic changes in the southern Amazon remains unclear. This study aimed to compare the thermal comfort indices in grass monoculture and integrated systems. The three systems were pasture under full sunlight (PFS), integrated (triple-row) livestock-forestry (ILFT), and integrated (single-row) livestock-forestry (ILFs), across four seasons, for two years, from June 2017 to June 2019. We assessed photosynthetically active radiation (PAR), air temperature, relative humidity, black globe temperature, and wind speed. Thermal comfort indices such as temperature-humidity index (THI), black globe temperature-humidity index (BGHI), and radiant thermal load (RTL) were calculated based on microclimate data daily-collected from 8:00 to 16:00. The ILFT mean THI (76.8) was slightly lower than ILFS and PFS. The BGHI and RTL values decreased as shading increased (PFS > ILFs > ILFT). The most challenging heat stress conditions for grazing animals occurred predominately during winter and autumn. In conclusion, the presence of trees in pastures of the southern Amazon improved the microclimate and, consequently, the thermal comfort indices. Agroforestry systems can foster an environment with a more suitable thermal comfort or less restrictive to animal performance, which contribute to mitigating global climate change for forage-livestock systems in Brazilian Amazon.