Lead author Jeremy Weiss, a senior research specialist in the UA department of geosciences, said: “We know the climate in the Southwest is getting warmer, but we wanted to investigate how the higher temperatures might interact with the highly variable precipitation typical of the region.”
Weiss’ team used a growing season index computed from weather data to examine limits to plant growth during times of drought. “The approach we took allows us to model and map potential plant responses to droughts under past, present and future conditions across the whole region,” explained Julio Betancourt, a senior scientist with the U.S. Geological Survey who co-authored the study along with Jonathan Overpeck, co-director of the UA Institute of the Environment. Betancourt holds adjunct appointments in the UA department of geosciences, the UA School of Geography and Development, the UA School of Natural Resources and the Environment and the UA Laboratory of Tree-Ring Research.
...A key source of plant stress, vapor pressure deficit is defined as the difference between how much moisture the air can hold when it is saturated and the amount of moisture actually present in the air. A warmer atmosphere can hold more water vapor, and during droughts it acts like a sponge sucking up any available moisture from the ground surface, including from plants.
Both droughts – with the more recent one occurring in warmer times – led to widespread tree die-offs, and comparisons between them can help sort out how both warming and drying affected the degree of mortality in different areas....
Mount Evans in Colorado, shot by Hogs555, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license
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