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By April 2015, water managers and agricultural producers in Idaho, Oregon, and Washington were facing a serious problem. Snowpack levels across all basins in the region were significantly below average, with some areas in western Washington and Oregon reporting as little as 7% of normal snow water equivalent (SWE) values (a measure of how much water is stored in snowpack). By April 1st, SWE values are typically at their highest, representing peak snowpack. The critically low levels in April 2015 indicated a severe “snow drought” in Idaho, Oregon, and Washington. Since 1980, snow droughts have become longer and more severe in the Northwest. As climate change progresses, long-term changes to regional snowpack could affect the ecology, economy, and culture of the region.
What are snow droughts?
Snow droughts are periods of abnormally low snowpack for a time of year in a particular location. Snow droughts can occur in two primary forms. Dry snow droughts occur when below-average precipitation leads to a below-average snowpack. Warm snow droughts occur when above-average temperatures cause precipitation to fall as rain instead of snow. Both types typically result in lower-than-normal SWE values. Alaska, Idaho, Oregon, and Washington all experience snow drought from time to time. These events can be natural and influenced by several factors, including atmospheric events like El Niño. However, climate change could increase the frequency and severity of snow droughts as temperatures rise and affect precipitation patterns.
How does climate change affect snow in the Northwest?
Snowpack serves as a natural reservoir, storing water for release during the drier summer months. This water is vital for river basins in Idaho, Oregon, Washington, and Alaska, supporting plants and wildlife, and sectors including agriculture, hydroelectric power, fisheries, and recreation. Most climate models project modest increases in precipitation by the mid-21st century, although summers are likely to be drier. Despite increased precipitation, snowpack continues to decrease in parts of Idaho, Oregon, Washington, and parts of coastal and Southeast Alaska. The average level of snowpack in the region is projected to continue to decrease over the 21st century. However, high elevation or very cold areas, such as Alaska’s Brooks Range, could see increases in snowpack.
Several factors contribute to decreasing snowpack. Rising temperatures are causing more precipitation to fall as rain rather than snow, particularly at low to mid elevations, which reduces snow accumulation. In addition, snow is melting earlier in the spring, shortening the snow season and affecting summer water availability. In parts of the Cascade Range, the snow season is projected to decrease by nearly half by the end of the 21st century. In southern and western Alaska, snowpack is projected to decrease by 20 to 60% by the 2050s under a moderate greenhouse-gas emissions scenario, although high-elevation and cold parts of the state could see higher snowpack.
Under these conditions, snow droughts, particularly warm snow droughts, are likely to occur more frequently in the future. Recent research points to possible increases in frequency having already occurred. Since 1991, snow drought occurrences have increased 10 to 15% in Idaho, Oregon, and Washington, with variability in drought type trends (i.e., warm versus dry snow drought). From 1999 to 2018, snow droughts also became longer and more intense than they were from 1980 to 1998. However, it remains to be seen whether these short-term trends will continue with time.
What can past snow droughts teach us about the future in the Northwest?
Snow drought can have cascading effects on the ecology, economy, and culture of the Northwest. The 2015 snow drought and other low-snowpack years show the potential effects of future snow droughts in Idaho, Oregon, Washington, and Alaska.
During the 2015 warm snow drought, precipitation levels were near normal. However, winter temperatures were 6.2 degrees F higher than average. These high temperatures caused precipitation that would normally fall as snow to fall as rain instead. When snow did fall, warmer temperatures caused snow to melt earlier than normal. This snowmelt, coupled with winter rain events, caused high peak streamflow and flooding during the winter. However, summer streamflow was far below normal, reducing the amount of water available for systems dependent on summer water availability.
As winter temperatures continue to rise, the region will likely experience earlier peak streamflow, contributing to lower water availability in summer. Extremely low summer flows in streams and rivers can lead to widespread fish mortality and drying wetlands that affect aquatic species, which occurred in Oregon and Washington in 2015. In Southeast Alaska, low streamflow levels and high stream temperatures have contributed to hypoxia events, or a lack of oxygen, causing high salmon mortality. Changes to snowpack can also affect plants, as is the case with Alaska yellow-cedar, a species in significant decline in some parts of Southeast Alaska due to rising temperatures and reduced snowpack.
Coupled with low spring precipitation and higher-than-average summer temperatures, the 2015 snow drought contributed to unusually dry dead fuels (wood and other dead vegetation on the ground), and very low moisture content in live fuels (e.g., conifer needles) in Northwest forests. These conditions contributed to high fire intensity and rates of spread during the 2015 fire season in Idaho, Oregon, and Washington. In fact, the 2015 wildfire season was one of the most severe seasons in recorded history, with more than 2.3 million acres burning across Idaho, Oregon, and Washington. As drought increases in severity in the Northwest, the frequency and extent of wildfires could also increase.
Snow drought can also impact agriculture in the region. Agricultural losses in Idaho, Oregon, and Washington reached nearly $1 billion in 2015, including extensive losses to raspberries, blueberries, and the dairy industry. Water-rights holders experienced water delivery cuts and short irrigation seasons. Some producers relied on groundwater pumping to supplement their water needs. If snow drought occurs more often, farmers may need to adapt their practices to suit drier conditions.
Snow- and water-based recreational activities can also be affected by snow drought. In 2015, several ski areas closed earlier in the season than ever before, and many struggled to stay open with low snow. For example, the 2015 ski season at Stevens Pass Mountain Resort in Washington was two months shorter than average, reducing visitation by over 50%. In the summer, low water levels in Detroit Lake, Oregon reduced visitation by 26% and rendered most boat ramps unusable. Yet, high temperatures extended the summer recreation season in some areas. In Oregon, 171 state parks reported a nearly 10% increase in visitation from 2014 to 2015. However, as the climate continues to warm, these gains could be offset by deteriorating summer conditions, such as increased wildfire smoke, more intense heat waves, and dusty trails associated with drought.
The 2015 snow drought in the Cascade Range was the most severe in 300 years. Researchers have compared this event to projected climate conditions for the 2050s under a moderate greenhouse-gas emissions scenario (RCP 4.5). Although climate models suggest similar winter temperatures in the 2050s, winter precipitation is expected to increase slightly by that time, which could reduce the severity of future snow droughts in comparison to the 2015 event. However, many of the effects of prior events are expected to recur as snow droughts become more common. This will pose significant challenges for farmers, ranchers, foresters, and natural resource managers.
How can we adapt to less snow in the Northwest?
Despite the challenges associated with snow drought, many options are available for adapting to more drought in the future. Farmers can diversify crops and crop varieties, shifting to drought- and heat-tolerant crops that can cope with less water. Irrigation efficiency can be improved with practices like drip irrigation, and practices like no-till and cover-cropping can help retain soil moisture. Ranchers can use adaptive grazing management to accommodate changing conditions. Livestock can be bred or selected for drought tolerance. Foresters and natural resource managers can thin and/or use prescribed fire in dense forest stands to reduce competition for water and improve resilience to drought, insects, and diseases. Alternative tree species or assisted migration (using drought-tolerant tree species and genotypes) can be considered for reforestation projects.
Natural resource managers can also restore and maintain natural water storage systems like wetlands and reservoirs, protect watersheds from erosion and sedimentation, and monitor water quality to ensure it meets the needs of ecosystems and human communities. Land management agencies, ski resorts, and other recreation-based industries can consider expanding summer recreation opportunities. For example, Stevens Pass Ski Resort diversified summer operations to include mountain biking, disc-golfing, and hiking. Implementing these and other strategies can increase regional resilience to snow droughts, helping resource managers strengthen the long-term sustainability of their operations and the ecosystems they manage.
