Quantifying the Anthropogenic Impact on Vapor Pressure Deficit Increases and Drying Trends over the Southeast Amazon

The Amazon rainforest plays a crucial role in the global climate system and the carbon cycle. However, recent decades have witnessed severe droughts and wildfires in the Amazon, leading to concerns about its potential to become an atmospheric carbon source. These events have profound implications for the escalating effects of climate change worldwide. Consequently, understanding the factors behind these droughts and their potential future severity is of utmost importance. Vapor pressure deficit (VPD), a key atmospheric variable associated with droughts, has shown significant overall increases across large portions of the Amazon. However, it remains unclear as to what degree natural climate variability and anthropogenic climate forcings contribute to these VPD increases. As such, we use a flow analog method to determine the degree of natural variability in the observed VPD increases. Our analysis reveals that analog circulations explain only a small portion of the observed VPD increases in the Amazon. Specifically, we find that only about 35% of VPD increases are explained by natural variability, with the other 65% of VPD increases due to anthropogenic forcings. Additionally, the VPD increases are primarily driven by factors related to temperature increases rather than moisture decreases. These findings underscore the role of human activities in driving changes in VPD and drought conditions in the Amazon. They highlight the urgent need for climate change mitigation efforts and sustainable land-use practices to preserve the Amazon's crucial carbon sequestration capabilities and mitigate the escalating impacts of climate change globally.