A Recent Systematic Increase in Vapor Pressure Deficit over Tropical South America

Abstract

We show a recent increasing trend in Vapor Pressure Deficit (VPD) over tropical South America in dry months with values well beyond the range of trends due to natural variability of the climate system defined in both the undisturbed Preindustrial climate and the climate over 850–1850 perturbed with natural external forcing. This trend is systematic in the southeast Amazon but driven by episodic droughts (2005, 2010, 2015) in the northwest, with the highest recoded VPD since 1979 for the 2015 drought. The univariant detection analysis shows that the observed increase in VPD cannot be explained by greenhouse-gas-induced (GHG) radiative warming alone. The bivariate attribution analysis demonstrates that forcing by elevated GHG levels and biomass burning aerosols are attributed as key causes for the observed VPD increase. We further show that There is a negative trend in evaporative fraction in the southeast Amazon, where lack of atmospheric moisture, reduced precipitation together with higher incoming solar radiation (~7% decade−1 cloud-cover reduction) influences the partitioning of surface energy fluxes towards less evapotranspiration. The VPD increase combined with the decrease in evaporative fraction are the first indications of positive climate feedback mechanisms, which we show that will continue and intensify in the course of unfolding anthropogenic climate change.

A Systematic Review of Slash-and-Burn Agriculture as an Obstacle to Future-Proofing Climate Change

“…Wildfires of the Amazon caused by slash-and-burn practices had resulted in a noticeable upsurge of atmospheric carbon monoxide and carbon dioxide (Lopes, 2019). Increased greenhouse gases and biomassburning aerosols from the wildfires set into motion a positive climate feedback loop which further increases the vapor pressure deficit and decreases evapotranspiration, leading to lower moisture in the atmosphere, hence less precipitation (Barkhordarian et al, 2019). This sets the path for a drier Amazonia and higher risks of wildfire (Barkhordarian et al, 2019).…”

“…Increased greenhouse gases and biomassburning aerosols from the wildfires set into motion a positive climate feedback loop which further increases the vapor pressure deficit and decreases evapotranspiration, leading to lower moisture in the atmosphere, hence less precipitation (Barkhordarian et al, 2019). This sets the path for a drier Amazonia and higher risks of wildfire (Barkhordarian et al, 2019). On the other side of the world, the Indonesian forest fires, also initiated by slash-and-burn practices, emitted an estimated 708 million tonnes of carbon dioxide equivalent, which exceeded that from the Amazon wildfires (366 million tonnes carbon dioxide equivalent) by approximately two times (Jong, 2019).…”

Grow wider canopies or thicker stems: Variable response of woody plants to increasing dryness

“…As dryness increases, increasing vapour pressure deficit and radiation increase the demand for both photosynthesis and transpiration (Barkhordarian et al, 2019), with species increasing either their leaf area for canopy expansion, or sapwood area for stem thickening, in order to maximize photosynthetic revenue or reduce the risk of hydraulic failure. Eucalyptus spp., the dominant woody genus, had wider canopies rather than thicker stems, as aridity increased.…”

Tenência do vapor de água na baixa Troposfera da América do Sul

“…Tendência de aumento no vapor de água tropical também foi documentada por Paltridge et al (2009) e Barkhordarian et al (2019). O incremento mensal de vapor de água na troposfera da América do Sul geralmente está inserido nos períodos onde se observa os maiores índices pluviométricos na região em análise.…”

“…Para as estações 82599 e 83840 o aumento decadal na média anual no vapor de água foi de 0,17 gkg -1 .O padrão observado nas estações 80222, 82332 e 82599 foi semelhante, com vários meses apresentando significância estatística. Parte do aumento no vapor de água atmosférico nestes meses ser explicada pela variabilidade natural do sistema climático(BARKHORDARIAN et al, 2019).…”