Water levels in reservoirs across Oregon are two-thirds below average as summer ends, but autumn and winter weather may not offer much help, experts say.
Mountain snowpacks that provide irrigation water and replenish reservoirs are facing another tough year as the “El Nino” atmospheric pattern bodes for warmer winter weather.
“There’s a lot of concern those reservoirs won’t fill,” said April Snell, executive director of the Oregon Water Resources Congress, which represents irrigation districts.
At this point, the deviation toward higher temperatures over winter is projected to be among the three most significant variations since the 1950s, said Tom Di Liberto, meteorologist for the Climate Prediction Center at the National Weather Service.
“We do expect it to be one of the strongest ones,” he said.
While a strong El Nino is reliably associated with warmer weather, the impact on precipitation is less clear — the event generally indicates drier conditions in Oregon, but that’s not inevitable, he said.
“El Nino is never a guarantee of a certain set of outcomes,” Di Liberto said. “Weather can be chaotic.”
Areas of low pressure tend to usher in storms toward the southern West Coast during El Nino winters, but it’s tough to say where this “anomaly” will be strongest, so the Northwest may also be affected, he said.
With higher temperatures, though, the precipitation isn’t as likely to come in the form of snow, he said.
Aside from El Nino, another significant weather pattern to watch is the Arctic Oscillation, which determines whether storms around the North Pole will spread out and impact lower latitudes.
This trend may either enhance or conflict with the effects of El Nino, though it’s too early to tell at this point, Di Liberto said. “Those are the type of patterns we don’t have a ton of predictability with.”
Soil moisture is another consideration heading into winter, as the ground must be saturated before snowpacks become available in the form of runoff, said Scott Oviatt, Oregon snow survey supervisor for the USDA’s Natural Resources Conservation Service.
“We’re worried that we’re going into the water year with a deficit,” he said, noting that some regions in Oregon have experienced several years of insufficient moisture. “That has made the situation worse and it’s why we’ve been so susceptible to wildfire this year.”
Despite the “exhausted” soils, it wouldn’t be desirable for Oregon to see “high intensity” precipitation that would lead to flash flooding, he said.
That risk is particularly acute in areas that have suffered from wildfires, since ash impedes the soil’s ability to take on water, Oviatt said.
It’s preferable for the state to encounter a progression of “low intensity” storms that will replenish moisture without overwhelming the soil, he said.
Low stream flows across Oregon in 2015 caused water regulators to shut off irrigation for junior water rights holders weeks ahead of normal, said Diana Enright, spokesperson for the Oregon Water Resources Department.
Water calls also went back further in time in terms of priority date — the John Day River, for example, was regulated back to 1876, while Fifteenmile Creek in the Hood River area was regulated back to 1861, according to OWRD. In other words, irrigators with more recent priority dates had irrigation shut off.
It was also unusual that irrigators in the Northwest corner of Oregon were subject to water calls, Enright said. In Polk County, for example, Rickreall Creek was regulated back to 1940 and the Luckiamute River was regulated to 1964.
Longtime area residents said they hadn’t experienced such shortages before, Enright said. “We don’t usually regulate in those areas.”
With the possibility that more precipitation will fall as rain rather than snow, the management of reservoirs may need to be reconsidered, said Snell of the Oregon Water Resources Congress.
Water is traditionally released during winter to ensure adequate flood control, but if recent conditions are the “new normal,” those requirements must be balanced against the need for adequate water during summer, she said.
If there is an upside to the drought, it’s that more people are thinking about the need for water supply management and development, Snell said. “It’s an eye-opener for folks.”