In thinking about the effects of climate change on our arid landscape, it’s easy to get distracted by precipitation numbers. Will it go up or down? How much? What’s the error bar look like? But in recent years, the research community that looks at the Southwestern U.S. has been banging away on “P minus E”. It’s not just the precipitation. It’s precipitation minus evaporation. Or, to be a bit more specific when looking at riparian systems in arid landscapes, evaporation (open water) and transpiration (the plants that live on a river’s groundwater).
In this morning’s Albuquerque Journal, I have a story (ad/sub req.) looking at this point through the latest research to tackle the question, by UNM climate scientist David Gutzler and research student Tessia Robbins. Journal photographer Greg Sorber and I went out to a stretch of bosque (the woods along the Rio Grande) to a site where scientists measure evapotranspiration:
In the summer, this stretch of bosque can lose the equivalent of a layer of water a quarter of an inch deep every day — far more than falls from the sky. The warmer it gets, the more this landscape dries out.
It is not the rain and snow that matters most, scientists like Cleverly say. It is the evaporation.
As Earth’s climate warms, scientists expect years-long dry spells and wet spells to continue, just as we have seen in the past.
But with warmer temperatures and the resulting increase in evaporation, it will be harder to recover from the dry spells, according to a new analysis by University of New Mexico professor David Gutzler and UNM research student Tessia Robbins.
“We’ll go into a big drought some time in the 21st century,” Gutzler said, “and we just may not pull out of it.”