Precipitation is big wild card for Idaho’s farmers

Southern Idaho’s irrigated agriculture is already feeling the rise in global temperatures.

“We’ve already been affected,” said Shirrel Silvester, a longtime farmer south of Twin Falls whose profitability has been hurt by weather extremes and instability.

“What you see outside your backyard is not the climate,” said Hans Peter Marshall, a geoscientist at Boise State University. Climate refers to weather patterns on a large scale, over large regions and for long periods. Climate change, however, will affect local weather.

The fluctuations that Silvester has seen are just the beginning.

“There are going to be weird years,” Marshall said, “when the weather fluctuates dramatically.”

Ag producers rely on somewhat stable weather patterns to decide what to grow, when to plant and when to harvest. Their living — and a major Idaho industry — depends on making good choices.

But with climate change, making those choices could become a crap shoot. It already is for Silvester.

He farms 520 acres in the Southern Idaho desert — 200 acres on the Twin Falls irrigation tract with water from a still-stable snowpack in the Wyoming Tetons, and 320 acres on the water-scarce Salmon tract, irrigated with water from a dwindling snowpack in Nevada.

Silvester’s farm on the Twin Falls tract, with its dependable irrigation, is typical of most farming in Southern Idaho for the past century. His Salmon tract farm, however, mirrors how many farms will operate as the temperatures rise.

The big wild card: precipitation. Next to sunshine, timely moisture is the most critical component to growing a crop. Precipitation is timely when it falls as snow in the mountains and as rain on the fields during the growing season.

Scientists, however, don’t know what impact climate change is going to have on precipitation in Southern Idaho.

“No one has a clue,” Marshall said. Some models say the area could get more rainfall; some say less.

Even if more rain falls, the mountain snowpacks — the ag industry’s largest reservoirs — will likely accumulate later and melt earlier. Most models show reduced snowpack in the Tetons — which feed the Snake River and thousands of farmers — by the end of the century.

Rainfall at the wrong time of the year can delay planting in the spring and disrupt harvest in the fall.

When water looks like it will be short, Silvester plants fewer acres. Some years on the unpredictable Salmon tract, “we’d only get one-tenth of our water allotment,” he said. “One-tenth, which is nothing.”

The wet fall of 2014 prompted Silvester to plant a lot of winter wheat. The rains stopped in February and he lost a whole pivot. Then a miracle occurred: A bit of rain fell in June, saving what little crop Silvester had left.

“The wheat headed out and the rain put water in the dam. I ended up with half yields on 100 acres — but I got something,” he said. “I didn’t have water to grow beans, corn or nothing else. I used all my water on grain.”

Warmer temperatures will eventually increase the Southern Idaho growing season by two weeks, said John Abatzoglou, associate professor of climatology at the University of Idaho. But what is good for a bean producer may not be so good for a pea grower.

Another mainstay of Southern Idaho’s economy is the dairy industry. With global warming will come heat waves that can stress and kill livestock, as well as reduce the availability of water, pasture and feed.

Animal-based production, including dairy, brings in about half the agricultural receipts in the U.S. But in Idaho, animal products such as meat, dairy and wool make up 63 percent of the state’s annual $8.7 billion agriculture industry. In 2014, animal products brought in $5.5 billion; plant-based products, $3.2 billion.

But owning livestock could be risky business in the future, and dairy is a thirsty industry. Many Idaho dairies rely on groundwater pumped from an aquifer fed by mountain snowpacks.

The global average temperature has risen 1.8 degrees since scientists started keeping track in 1880, Abatzoglou said. But despite rising temperatures, the high mountains in critical areas of Idaho and Wyoming will still get snow.

Even with less snowpack in the mountains, “we’ll have better snowpack than most areas,” said Ron Abramovich, water supply specialist for the Natural Resources Conservation Service in Boise.

This story was originally published December 27, 2015 at 11:28 PM with the headline "Precipitation is big wild card for Idaho’s farmers."