ALBUQUERQUE, N.M. — When the latest seasonal drought forecast came out Thursday, reader Ken asked: “When does a drought become the new norm; that is, it’s no longer a ‘deficiency’ and so no longer a drought?”
It’s a good question, with no easy answer, because it gets to the heart of what we mean by “drought” — as we’ll see, a slippery, ill-defined term that sometimes conceals as much as it reveals. If long-term aridity becomes the norm in New Mexico as a result of a changing climate, will we stop calling it “drought” and just cope?
We’re in a big hole. New Mexico precipitation over the past 24 months has been the lowest since 1955-56, the worst of the drought of the ’50s. With a few notable exceptions, the state’s reservoirs are nearly empty. Lake Sumner on the Pecos in eastern New Mexico is “an evaporative muck pond,” John Longworth of the Office of the State Engineer said during a state drought meeting Monday. Ninety-one percent of the state’s grazing rangeland is in poor or very poor condition.
Precipitation in the mountain watersheds that collect New Mexico’s water supply via winter snow is less than half of normal for this point in a typical season, according to Wayne Sleep, a member of the federal government’s New Mexico snow survey team. “It’s not a promising start to the snow season,” Sleep said Monday.
I feel Ken’s angst. New Mexico is warmer and drier now than it’s been anytime before during the two decades I’ve lived here. The prospect of a third drought winter in a row puts me in mind of Southern California’s Santa Anas, the dry desert winds of my youth, which Raymond Chandler said “curl your hair and make your nerves jump and your skin itch.”
But there’s something more than a lack of rain and snow behind Ken’s question. Rainy spells and dry spells come and go. But that natural variability is now superimposed on a long-term warming trend, the result of a planet warmed by rising greenhouse gases. So while New Mexico has been slightly wetter the past two years, compared with 1955-56, according to the National Climatic Data Center, it also has been substantially warmer — 1.7 degrees Fahrenheit on average.
“It’s gotten warmer,” said University of Arizona researcher Dave Breshears, who tracks drought’s effect on forests, “and it’s going to keep getting warmer.” Higher temperatures mean more evaporation from soils, more transpiration from plants (and, in tough times, more stress on plants), less water in streams and rivers.
So does that mean droughts are getting worse as the planet warms?
That depends a great deal on what we mean by “drought.” “Quantifying drought is a very difficult business,” said University of New Mexico climate scientist Dave Gutzler.
By one definition commonly used by scientists known as the Palmer Drought Severity Index, which looks at both temperature and precipitation, the answer may be “no.” A fresh look at Palmer measurements globally suggests “there has been little change in drought over the past 60 years,” Princeton researcher Justin Sheffield and his colleagues wrote in a paper published last week in Nature.
Other scientists have come to a different conclusion, arguing there has been a global increase in drought as a result of the planet’s temperature. The debate shows how sensitive the question is to the details of how you define and measure “drought.”
The Palmer Index shows similar results to Sheffield’s when you drill down to New Mexico — the drought of the 1950s was, at its worst, similar to the current situation here. But it lasted far longer — eight straight years of bad drought. In our current drought, three of the past eight years have been wetter than average. A second drought, beginning in 1898, also looks worse by that measure than today’s conditions in New Mexico.
But if your measure of drought is the combined stress of rising temperatures and lack of moisture on Southwestern forests, the drought of the past decade is significantly worse than the droughts of 1898 or the 1950s, according to an analysis by Los Alamos National Laboratory researcher Park Williams. Ditto if your measure is the amount of water flowing through the Colorado River Basin, providing vital supplies to New Mexico, six other western U.S. states and Mexico.
The drought of the past decade has been far worse in terms of Colorado River supplies than anything else we’ve seen over the past century, raising questions about the long-term viability of water supplies in cities from Albuquerque and Denver to coastal Southern California.
“Drought,” University of Arizona research Gregg Garfin said, “is defined by its impacts.”
I realize this is a long-winded way of being very unhelpful to Ken, whose question started all my inquiries. My simpler answer, Ken is, “Depends on what you mean by ‘drought.’ ”
UpFront is a daily front-page opinion column. Comment directly to John Fleck at 505-823-3916 or firstname.lastname@example.org. Go to ABQjournal.com/letters/new to submit a letter to the editor.
— This article appeared on page A1 of the Albuquerque Journal