Recent storms and mountain snow delivered short-term drought relief created happy farmers, brought wildflowers that add color to attract tourists and replenished the water supply.

But is one month of above-average precipitation enough to wipe away a decade-long drought in the Southwest? Not according to climate researcher Ben McMahan.

“When comparing drought improvement, we have to remember the long term vs. the short term.  It takes time for the long-term deficit to build up. One great month didn’t really make up the difference of the next couple months not being that great,” said McMahan, research outreach and assessment specialist for the Climate Assessment for the Southwest (CLIMAS) program.

McMahan said that although the recent January rains have been a pleasant surprise during a La Niña year — which is typically characterized with below-average precipitation — the region still faces long-term drought recovery.

Nick Buckelew, a Tucson-area farmer from Buckelew Farms, is content for any rain his farm can get.

“We pump groundwater from the Altar Valley basin and since there are very few wells in the valley, our water table is stable and hasn’t changed in the 62 years we have been farming here,” Buckelew said. “Local rains do help supplement irrigation and help recharge our underground aquifer.”

The National Weather Service reported that 1.18 inches of rain fell at the Tucson International Airport in January, which is 0.24 inches above normal for the month, after a parade of three back-to-back storms slammed the West.

The result left many other locations in the Western U.S. with above-average precipitation in January 2017. The figure below illustrates above-average rainfall for the month in green, blue and purple, with below average precipitation represented by the yellow, orange and red hues.  (See figure showing departure from average precipitation For Western U.S.)

With all this talk about La Niña, what is it anyway?

La Niña is a periodic cooling of the equatorial waters of the Eastern Pacific Ocean. That cooling has far-reaching effects on global weather patterns. For Arizona, it typically means the state can expect a drier winter than average. There are exceptions, as happened last year with El Niño — a warming of the waters in the same equatorial Eastern Pacific, which typically brings wetter-than-average winters to Arizona. In 2016, the state saw a very wet January, followed by an extremely dry February and March.

“When it is a weak La Niña, it is not a real strong correlation, so I wouldn’t count on anything, especially after last year was a strong El Niño and we got nothing,” said Ken Drozd, warning coordination meteorologist for the National Weather Service.

Drozd said the chances for beneficial rains this winter are still decent, due to a weak La Niña pattern, but said La Niña is only one of many factors that can bring storm systems into Arizona during the winter months.

“Yes, we say all these recent storms have helped, and there is quite a bit more streamflow forecast because of the snowpack in the mountains,” McMahan said. “The question will be, does it warm up and melt some of that snow early, so it runs into the reservoirs sooner or evaporates faster?”

In many cases, major reservoirs in Arizona are at about the same water level as this time last year, of which most are still below-average. By looking at the figure below, the current water levels of eight of Arizona’s major reservoirs can be seen and compared to last year’s levels, as well as the average water levels in each reservoir. (See Current Reservoir Levels Map below)

Still, any amount of rain helps the state inch toward healthier reservoir levels.

“That little uptick still matters, but when you do think about the long-term trend it does not add quite as much as what you might have hoped,” said McMahan when referring to the long- term drop in water levels on crucial reservoirs of the Colorado River such as Lake Mead and Lake Powell.

These reservoir water levels have dropped to where they are now for five years, and it would take a sustained period of time of above average rainfall to get them where they should be, he said. (See Lake Mead Figure below)

Although it is common for the Sonoran Desert to be extremely hot and dry for extended periods of time, it is the only desert in the world with two wet seasons: the cool season, and the warm season.

The cool season runs from October to May, and the warm season runs from June through September. During the cool season, the winter storm systems tend to be more widespread as they move across the area, dumping decent amounts of precipitation over larger areas and longer periods of time. The warm season, or monsoon thunderstorm season, is characterized by more intense, spotty storms that dump large amounts of rain in short periods of time.

Monsoons bring welcomed relief from the scorching summer heat and provide a rejuvenating drink to the native plants of the area, but the real beneficial rains come in the cool season, when gentle, steady rains cover larger areas. According to McMahan, these winter rains can put a dent in the long-term drought by replenishing the groundwater and reservoir supply. (See Drought Map below)

“It is not always about how much rain fell, but how often it rained,” McMahan said. “Was it spaced out over a period of time, or did it all come in just three or four days?”

In other words, long-term drought conditions are recorded in months and years, not days and weeks, McMahan said. “It takes a while to recover from structural deficits,” he said.“Even with great years it is not going to radically rebound.”

McMahan said it is important to keep a long-term perspective. “Last year we had great El Niño storms and we had the media calling saying, ‘Is this El Niño?’ and then two weeks later it was dry, and then the story is … ‘I thought you said this was going to be El Niño? I thought it was going to rain a whole bunch.’ ”

Taylor Dayton is a reporter for Arizona Sonora News, a service from the School of Journalism with the University of Arizona. Contact him at [email protected] 

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