Becoming hotter makes it drier

New Mexico is three degrees hotter than it was half a century ago. That is established fact. It’s probably going to continue to get warmer and drier, but that is prediction based on probability and could change.

Three degrees doesn’t sound like much to me, but the difference it makes in the climate is profound, in part because of the relationship between temperature and water.

This is described in an article in “New Mexico Earth Matters,” published quarterly by New Mexico Tech. The author is David Gutzler, Professor of Earth and Planetary Sciences at UNM.

The author calls this current warming trend a new climatic phenomenon. “In the past,” Gutzler writes, “people in the Southwest learned to respond to climate fluctuations – sometimes, with no other choice, by moving. Now, however, humans are an intrinsic component of the climate system itself.”

Both temperature and precipitation vary from year to year, but temperature has been creeping up. Average annual precipitation has stayed about the same. What’s different is timing: when it rains or snows and when the snow melts.

The Rio Grande relies heavily on snowmelt from the northern mountains. The the snow melts earlier in spring than it used to, so the river is not flowing adequately in the summer when water is most needed. This year is an example: plenty of snow in winter followed by an early spring warm-up, causing very dry conditions this summer.

Years of sufficient water and years of drought don’t simply alternate one year at a time, the measurements show. Like the seven years of abundance followed by seven years of famine in the Bible, the patterns repeat for several years, so the effect of the drought gets worse before being relieved.

According to the U.S. Drought Monitor, which has only existed since the year 2000, New Mexico’s longest period of drought since 2000 lasted 329 weeks from May 2001 through August 2007.

In one of those years, a member of a cattle ranching family I know told me her family was going to have to sell off their stock. I was relieved that they did not have to sell the ranch. That is a cautionary tale for us all. To run a business with so much uncertainty takes both courage and great flexibility.

Gutzler observes that vegetation is likely to change as the climate gets a little warmer and drier. Big trees may not survive. He suggests by the end of this century, if the current rate of change continues, the forested Sandia Mountains outside Albuquerque might resemble the Franklin Mountains near El Paso, treeless and much more barren.

I keep looking at a big blue squiggle on the map, which to me is not only a body of water but also an evaporation basin: Elephant Butte Lake. The dam was built about a century ago. Why did those engineers decide to build a dam that could store more than 2 million acre-feet of water in a valley that concentrates the summer heat?

As much as one third of the average annual inflow is lost to evaporation. In recent years the lake has been as low as 3% of its capacity. It’s currently reported to be at about 10% of capacity.

So I question whether that lake continues to be a practical place to store the water that we hope will keep southern New Mexico agriculture alive for the next half century. I am not the only one asking that question.

We are right now in a moment so stressful it seems almost unrealistic to talk about long-range issues. But change is happening, faster than we want and in ways we don’t like. Maybe the pandemic we’re now living through is a lesson: if we don’t act to mitigate it, it just gets worse.

Triple Spaced Again, © New Mexico News Services 2020

 

 

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