By Jason O’Brien, OSU Forestry and Natural Resources Extension – Oregon Master Naturalist Program Coordinator

The media is buzzing with reports about fire, drought and extreme heat. And climate change is often attached to these stories. But does climate science explain how today’s extreme weather relates, if at all, to global climate change? This article will highlight some of these relationships.

First, let’s review definitions of weather, climate and climate change. Weather is the state of the atmosphere at a place and time that determines if it is hot, dry, sunny, rainy, windy, etc. Climate is the average weather condition (e.g. average temperature) over time. Climate change is a change in the typical or average weather of a region or city. This could be a change in a region’s average annual rainfall, for example, or a change in a city’s average temperature for a given month or season. Under normal conditions, a range of weather conditions that deviate from averages (e.g. severe, extreme storms) can exist. Such extremes are not necessarily related to climate change.

Weather this year

June-Aug_AveTemp
This map shows that Oregon’s average temperature over three months in 2015 (June, July and August) was the warmest on record. Source: National Centers for Environmental Information (NCEI) – National Oceanic and Atmospheric Administration (NOAA)

2015 has been a significant year for extreme weather in Oregon, in particular, temperature and drought. According to a search of average temperatures in 2015 from January through August (the latest data available), Oregon has had the warmest year on record, departing from the 20th century average by an increase of 5.0°F1. The warm winter temperatures created a situation where Oregon’s snowpack peaked at the lowest levels measured in the last 35 years, with 60-90% below normal amounts in the western Cascades, and melted 3 months early (eastern Oregon fared only slightly better)2. This has resulted in severe or extreme drought conditions over much of Oregon despite precipitation levels being only moderately below average3. As of the writing of this article, Oregon Governor Kate Brown has declared drought declarations in 25 of the state’s 36 counties4.

Is this climate change?

All of this current weather leads many to ask if it is related to climate change. Climate scientists say that it is hard to attribute the current drought directly to climate change. Rather, they suggest that it aligns with anomalous patterns in the jet stream, a warm patch of ocean water off the PNW coast (the “Blob”), and a strengthening El Niño. That said, it is important to put such extremes into context according to the latest climate change science. Climate scientists project that average annual temperatures will increase in the Pacific Northwest 3°F to 10°F by the end of this century (compared to the period 1970 to 1999), depending largely on how much heat-trapping gases (Carbon dioxide (CO2), Methane (CH4), Nitrous oxide (N2O)) accumulate over this timeframe5. Temperature increases are projected to be largest in summer. For precipitation, projections are for a 10% reduction in rainfall during the summer5. Additionally, the April 1st snowpack, an indicator of natural water storage available for the warm season, is projected to decline by as much as 40% in the Cascades by the 2040s6. In other words, the “extreme” warm and dry weather we’ve experienced this year may be more like an “average” year in the future, whereas the future extreme years will be even more extreme.

 

What does this mean for our environment and for us?

Temperature

The past summer was the warmest on record for the Pacific Northwest. Climate model projections indicate that the largest increases in temperature will occur during the summer months5. Large increases in summer temperatures, along with decreased precipitation expected during this same period are likely to impact forests. These will be driven by water deficits, increasing tree stress and mortality, vulnerability to insects, and fuel flammability5. Further, forest managers will need to adapt to these changes, which will affect the plant hardiness zones for the most economically valuable tree species. This is particularly challenging when viewed over the entire life of a tree, when decisions about rate of growth and time to harvest must be planned. And, the ecology of whole forest ecosystems is projected to change (e.g. subalpine & alpine forests), threatening associated wildlife species7.

Wildfires

Cornet-Windy Ridge Fire on August 12, 2015
Cornet-Windy Ridge Fire on August 12, 2015. Source: InciWeb – Incident Information System, National Wildfire Coordinating Group (NWCG)

Extreme temperatures and drought during the driest months of the year are likely to bring more severe and larger wildfires, exacerbated by historic fire suppression practices. Already this year, Oregon has experienced wildfires that have destroying dozens of homes, consumed thousands of acres of forest, shrub and grassland, and in Washington, claimed the lives of three wildland firefighters. As the 2015 fire season begins to wind down, Oregon has experienced nearly 600,000 acres burned8.

 

What other extreme events might we expect with a changing climate?

Heavy Rain, Floods, and Landslides

In 1996, the Willamette Valley and parts of the Coast Range were hit by massive flooding. Heavy rain events in January, followed by cold temperatures, heavy snowfall in the Cascades, and more heavy rain and warming temperatures, created the right conditions for this flood, which struck in February9. According to climate models, we could expect more high rain events during winter and spring months. Regional climate models project increases of up to 20% in extreme daily precipitation5.

Flooded Willamette River, February 1996.
Aerial view of flooding along Oregon’s Willamette River in February 1996. National Weather Service Portland / Courtesy of U.S. Army Corps of Engineers. Public Domain. Source: http://www.wrh.noaa.gov/pqr/gallery3b.php

Averaged over the Pacific Northwest, the number of days with more than one inch of precipitation is projected to increase 13% during a 30-year period from 2041 to 2070, compared with 1971 to 2000.

This scenario assumes current rising emissions trends. Increases in heavy downpours, similar to the winter of 1996, could increase flood risk in mixed rain-snow and rain-dominant watersheds, such as in the Cascades and Coast Range. Further, landslides could increase due to soil saturation, combined with intense human development and unstable slopes6. This presents relevant challenges to forest managers as they consider when and where to harvest, establish roads, and consider the effects of runoff on sensitive fish-bearing streams and rivers.

The Upshot

Extreme weather events viewed in isolation are not necessarily tied to climate change. However, climate models project more extreme weather conditions related to temperature and precipitation. Combined with the effects of human management decisions over the last century, these changes in climate may mean more severe consequences to our environment, economy and society. How we handle these situations is a matter of our ability to adapt and mitigate for extreme events over the next century.

Citations:

  1. National Centers for Environmental Information (NCEI) – National Oceanic and Atmospheric Administration (NOAA): http://www.ncdc.noaa.gov/temp-and-precip/climatological-rankings
  2. Oregon Basin Outlook Report, June 1, 2015. USDA-NRCS. 37pp. Taken on August 19, 2015 from ftp://ftp.wcc.nrcs.usda.gov/states/or/watersupply/2015/WSOR_2015_Jun.pdf
  3. Palmer Drought Severity Index. US Drought Portal. Taken on August 19, 2015 from https://www.drought.gov/drought/content/products-current-drought-and-monitoring-drought-indicators/palmer-drought-severity-index
  4. State of Oregon Water Resources Department: Drought Watch. Taken on August 19, 2015 from http://www.oregon.gov/owrd/pages/wr/drought.aspx.
  5. National Climate Assessment – Northwest. 2014. http://nca2014.globalchange.gov/report/regions/northwest.
  6. USGCRP (2009). Global Climate Change Impacts in the United States . Karl, T.R., J. M. Melillo, and T. C. Peterson (eds.). United States Global Change Research Program. Cambridge University Press, New York, NY, USA. http://globalchange.gov/usimpacts/pdfs/climate-impacts-report.pdf
  7. Shafer, S., Harmon, M., Neilson, R., Seidl, R., St. Clair, B., & Yost, A. The Potential Effects of Climate Change on Oregon’s. http://www.fs.fed.us/pnw/olympia/silv/publications/opt/660_ShaferEtal2010.pdf
  8. InciWeb – Incident Information System. Taken on Sepember 25, 2015 from http://inciweb.nwcg.gov/state/38/20/.
  9. Flood of 1996: Nearly two decades ago, huge flood struck Portland, Oregon City. The Oregonian. February 10, 2015. http://www.oregonlive.com/history/2015/02/flood_of_1996_two_decades_ago.html
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