“Our analysis suggests these ecosystems may have crossed an ecological threshold,” they said, describing a breakdown in the relationship between precipitation and vegetation cover beginning around 1999.
In the Sonoran Desert and nearby landscapes, the scientists found, vegetation cover declined much more sharply than drought or wildfires alone could explain. Satellite observations between 1984 and 2017 showed “widespread” declines in perennial vegetation cover, the researchers wrote, especially in lowland deserts.
In the lowlands, modeling revealed that temperature explained much of the desert’s vegetation change, according to the study. Rising heat was also the best explanation for vegetation declines over the long term, as precipitation and wildfires have swung wildly from year to year.
The importance of heat surprised even the researchers.
“Many plant species in desert ecosystems have adaptations that allow them to withstand high temperatures, making this observation somewhat unexpected,” they wrote.
More research is needed to explain the mechanism behind that relationship, the authors added. One possible reason is that hotter weather makes water evaporate more quickly, creating even worse water stress on plants during the hot summer months.
The implications of the research could be dire.
Drought conditions have caused mass plant death in Southern California. That has changed the way the ecosystem responds to climate shifts, the researchers wrote. Notably, it seems to have broken down the once-predictable relationship between rain and vegetation cover.
“One potential implication is that it will be very difficult to predict future responses to changing environmental conditions. This could pose an important limitation to our ability to understand how drylands will be affected by future climate change,” they wrote.
Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2021. E&E News provides essential news for energy and environment professionals.