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How soon the monsoon?

ISAIAH BRANCH-BOYLE/Durango Herald

Florida Mesa farmers who use irrigation water from Lemon Reservoir, such as Joel Craig at Craig Limousin Ranch, likely will have water turned off early in July.

By Emery Cowan Herald staff writer

As forest vegetation continues to lose moisture and fields of alfalfa begin to turn from green to brown, farmers and firefighters are looking to summer monsoons as one of the last possibilities for some relief from summer’s intense grip.

“We’re really waiting to see what happens. Monsoons can make it or break it,” said Chris Tipton, a fire management officer with San Juan National Forest’s Columbine Ranger District.

Monsoons can bring a halt to fire season and, for farmers, an extra cutting of hay. But the National Oceanic and Atmospheric Administration notes monsoons are a fickle phenomenon

The North American Monsoon System, the summertime weather pattern that brings much-needed precipitation to the southwestern United States and Mexico, is perhaps the least understood of all the large-scale circulation patterns affecting the United States.

Yet climatologists are doing their best to put their finger on when Southwest Colorado could see the start of monsoon. At this point, forecast models indicate a low probability that monsoonal moisture will drench the region within the next two weeks. Southwest Colorado likely will see some precipitation, as it did in bursts over the weekend, but it won’t be the monsoonal moisture drawn up from the tropics due to the current location of high and low pressure zones, said Joe Ramey, meteorologist with the National Weather Service.

“There is a pretty good signal that we’re going to see increasing showers, but it’s not the classic monsoon 1-inch-per-hour rains and local flooding,” Ramey said.

The weather service’s two-week outlook calls for a greater than 40 percent chance that the region will receive above-normal precipitation, as opposed to the usual 33 percent chance of above-normal precipitation.

This is an El Niño-neutral year, meaning that the climate isn’t strongly influenced by the warming or cooling of sea-surface temperatures in the Pacific Ocean that define the El Niño or La Niña climate phenomena. That makes it harder for climatologists to make their forecasts, said Chris Cuoco, a senior meteorologist with the National Weather Service.

“When El Niño is strong or La Niña is strong there is more to hang their hat on,” Cuoco said. “Now it’s straight climatology and looking at the averages.”

Climate change and monsoons

Though difficult to pinpoint, the general timing of the summer monsoons is fairly reliable, meteorologists said. That will likely change in the coming decades, according to a report by researchers with NASA and Columbia University’s Lamont-Doherty Earth Observatory. The report predicts that over the next century, global warming will push the monsoon season later in the year, resulting in the heaviest precipitation falling in September and October, rather than July and August. Though the model focused on monsoon behavior over Mexico and the southern portions of New Mexico and Arizona, scientists expect to see similar changes in monsoon behavior in Colorado, Ben Cook, the study’s lead author, wrote in an email to the Herald.

The shift could lead to lower crop yields because rain would come later in the growing season and could also lead to increased wildfire risk by prolonging hot and dry conditions during the spring, Cook said.

“For many monsoon areas, the winter and spring is generally quite dry, so the start of the monsoon is critical for recharging moisture in the system,” Cook wrote in the email. “Delay that, and you extend the dry season and the time during which ecosystems, people and crops are moisture stressed.”

Farms, forests desperate for moisture

The impacts of less-than-average winter precipitation and a dry, windy spring season are taking a toll on agriculture throughout the county.

On Wednesday, La Plata County was one of seven southern Colorado counties the U.S. Department of Agriculture declared primary or contiguous disaster counties because of the severity of drought gripping the region. The designation makes farmers and ranchers in the area eligible for drought assistance.

Many local farmers are expecting to get only one cutting of hay before their irrigation water runs out. Florida Mesa farmers who use irrigation water from Lemon Reservoir likely will have water turned off early this month, said Philip Craig, a member of the Florida Water Conservancy District’s board of directors.

The monsoons could make a huge difference at this point, allowing farmers to produce enough of a crop to get a second hay cutting, Craig said.

He didn’t hold out much hope of that happening though.

“On a normal year we get just enough (moisture) to keep (the crop) alive,” he said.

Vallecito Reservoir irrigators will fare a little bit better, with irrigation expected to continue into August, said Hal Pierce, superintendent of the Pine River Irrigation District. Monsoon rains would help slow down the rate of the reservoir’s depletion, but if irrigators use all of their allotted water, the reservoir will finish the summer just 12 percent full, Pierce said.

The area’s forests also are in desperate need of moisture. Since forest officials started measuring in May, the moisture levels of smaller vegetation like Gambel oak and perennial grasses have been dropping precipitously. Larger trees like ponderosa, piñon and juniper are still pulling up snowmelt moisture from deep in the ground, but they are now starting to level and will soon start to dry out again, said Chris Tipton, a fire management officer with the Forest Service.

The moisture levels of small plants like grass, Gambel oak and sage are especially crucial in terms of the initial progression of a fire, Tipton said. Higher moisture levels in those plants can effectively stop or slow fire progression, giving firefighters time to respond, he said.

Even if rain doesn’t fall, days when there is more moisture in the air are beneficial in reducing fire risk and slowing the spread of fire if it does start. That’s because smaller plants, needles and dead leaves will absorb ambient moisture until they reach an equilibrium with the relative humidity levels.

Humidity and fuel moisture levels can make the difference between a fire growing to one-tenth of an acre versus 2 acres in the time it takes for firefighters to respond, Tipton said.

ecowan@durangoherald.com

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