Despite close to normal precipitation averages, Oregon’s drought continues to worsen, according to local climate experts. 

“This year’s drought was more severe than the precipitation totals suggest,” said Larry O’Neill, the state climatologist with the Oregon State Climate Service and associate professor at Oregon State University’s College of Earth, Ocean and Atmospheric Sciences.

According to O’Neill, a number of factors go into determining the severity of drought in a state. While rainfall is a part of this, it is also important to look at the heat from the summer, the snowpack in the mountains and how early the snowpack melts out.

“This summer was the warmest summer on record in Oregon by a substantial margin,” O’Neill said. “The heat pulled additional moisture out of the soil and plants than normal, which was visually evident pretty much everywhere you looked in Oregon this summer.” 

According to O’Neill, the hotter temperatures are a double edged sword. They increase the evaporation from plants and fungi as well as the soil, which leads to drier conditions. At the same time, when it does rain, the rain gets less absorbed and the soil remains drier.

The hotter temperatures also affect the snowpack, according to O’Neill. With hotter temperatures the snowpack melts earlier than normal. Even with a normal or above average snowpack, when there are extraneous conditions such as this summer’s heat, the snowpack melts too early and drought gets worse.

“Snowpack is a key predictor for streamflows and water supply through the following summer,” O’Neill said. “Usually snowpack can differ substantially from the precipitation total alone. Even with close to normal precipitation, a low snowpack or one that melts out too early in the spring often leads to drought during the following summer; these are termed as snow droughts.”

According to Philip Mote, a CEOAS professor, the water year is a metric used by most climate scientists to measure the rainfall averages and conditions of a year, defined as Oct. 1 to Sept. 30.

“The past 2020-21 water year was drier than usual but not extreme,” Mote said. “In any case, annual precipitation fluctuates commonly by [about] 25% or more, and so this year certainly isn’t unusual.” 

According to O’Neill, even if Oregon had an above average water year, it would still be in a drought. It could be made better by a higher amount of precipitation, but drought is also dependent on temperatures and when the snowpack melts out, as well as the size and health of the snowpack.

“We’ll get some snow [in the Cascades], hard to tell at this point whether it will be above or below normal and where,” Mote said. “Sometimes with La Niña events—as is happening this winter—parts of Oregon experience above normal snowfall, but in recent years the persistently warm winters have counteracted that tendency. Lower elevations are more affected by warming—since warming raises the snowline—than higher elevations.”

Every year since 2015 has been the warmest on record, making those years the warmest in human history, according to Climate Central, a nonprofit organization that reports on climate change science. 

Oregon is not immune from the effects of climate change. A normal water year is not enough to remove Oregon from drought; it requires a combination of circumstances, according to O’Neill.

“Scientific evidence indicates that human-caused climate change makes the ongoing drought worse, causes the snowpack to melt and leads to more and larger wildfires,” CEOAS professor Andreas Schmittner said. “Those phenomena are related. Warming leads to more evaporation, which reduces soil moisture and leads to drought in the summer… As long as humans keep emitting large amounts of carbon dioxide and other greenhouse gases to the atmosphere, and [the] climate keeps getting warmer, there will be a long-term trend towards more drought, less snowpack and more [and] larger wildfires.”

The conditions present the past few summers in the Pacific Northwest will continue to worsen unless major efforts are made in order to reduce the amount of greenhouse gases that are produced, according to Schmittner.

“One major communication point I like to make is that it is true that we have had natural cycles of droughts and wet periods in Oregon and the Pacific Northwest,” O’Neill said. “Even in a changed climate going forward, we will continue to experience wet periods, so if we have a year or two of relatively wet winters, that doesn’t mean that climate change is not occurring. What is projected to occur is that drought periods will become longer and more severe. The impact on society, particularly in the U.S. West, will also be more severe than we have historically experienced.”