Introduction
In Oregon, throughout the United States and across the globe, the climate is changing. These changes affect terrestrial and aquatic ecosystems and humans worldwide. The following are among the effects of climate change in the Western United States:
- Temperature increases.
- Increases in wildfire frequency and size.
- A longer fire season.
- More frequent and severe droughts and heat waves that last longer.
- Decreases in snowpack.
As a forest owner, you may have questions about how climate change will affect the trees on your property. This fact sheet describes some of the observed and projected climate changes in Oregon. How are temperature, precipitation and drought expected to change over the next 50–75 years?
Although there is some uncertainty about the extent to which values of these variables will change, there is no doubt that the climate is changing. Most of the climate-related content in this fact sheet is drawn from the seventh Oregon Climate Assessment, CC-BY-NC-SA.
A snapshot of observed and projected climate change
Observed: what measurements over time reveal about changes in Oregon’s climate
- Annual average temperature increased by about 2.2°F (1.2˚C) per century since 1895.
- Maximum and minimum temperatures have increased from 1895 to the present.
- Over the past 20 years, the incidence, extent and severity of drought in the Northwest increased. Low precipitation contributed to most droughts, but high temperatures and a shift from snow to rain also affected drought occurrence and severity.
Projected: how climate is likely to change in the future
- As warming continues and mountain snowpack decreases, the frequency of droughts will increase.
- Precipitation will increase during winter and decrease during summer.
- The amount of precipitation that falls in the strongest winter storms will increase.
- The proportion of precipitation falling as rain rather than snow will continue to increase.
Projected changes
1. Increase in frequency, duration and magnitude of extreme heat
Selected ecological impacts
- Increased water stress to some species of trees, depending on their ecological tolerances
- Shift in location and amount of habitat of some trees and other plant and animal species
- Potential for rise in pathogens and localized increases in populations of some insects, such as bark beetles
Selected social and economic impacts
- Increased heat exposure, especially among outdoor workers
- More heat-related deaths, illnesses and hospitalizations
- Increased energy use for cooling
2. Shift from snow to rain — reduced amount and duration of snowpack
Selected ecological impacts
- Loss of natural water storage and reduced late-season streamflows
- Reduced amount of habitat for some cold-water fish species during warm seasons
Selected social and economic impacts
- Reduced water availability for irrigation and hydroelectric power generation
- Changes in the economic viability of some winter and summer recreational activities
3. Increase in duration and magnitude of drought
Selected ecological impacts
- Increased water stress to some trees
- Shift in location and amount of habitat of some trees and other plant and animal species
Selected social and economic impacts
- Reduced water availability for agricultural, domestic and municipal use
4. Increases in wildfire frequency and size
Selected ecological impacts
- Increased tree mortality
- Potential reduction in water quality
- Potential obstacles to tree regeneration
- Local shifts from tree-dominated to shrub-dominated ecosystems
Selected social and economic impacts
- Loss of timber
- Temporary reduction in surface water quality
- Adverse human health impacts due to more frequent and denser smoke
- Potential for temporary or permanent human displacement
Effects of climate change on temperature, precipitation and drought across Oregon
Temperature
Oregon is becoming warmer. Despite relatively stable long-term precipitation totals, the state is more prone to drought. Oregon’s temperatures are projected to continue increasing in all seasons, particularly summer.
Relative to 1950–2014, Oregon’s annual average temperature is projected to increase by 2.6–3.0°F by 2044, 4.6–5.9°F by 2074 and 5.9–9.1°F by 2100, depending on the emissions scenario (Figure 1A).
Current scenarios of climate change, known as shared socioeconomic pathways or SSPs, represent assumptions about levels of greenhouse gas emissions and associated human behavior. SSP 2-4.5 assumes that carbon dioxide emissions plateau and then gradually decline by midcentury. SSP 3-7.0 assumes a doubling of greenhouse gas emissions by 2100. SSP 5-8.5 assumes that carbon dioxide emissions double by 2050.
Relative to the period 1901–2000, the average temperature in Oregon has been warmer than normal in 21 of the last 24 water years (Figure 2). Warmer temperatures contribute to higher rates of evapotranspiration and more frequent drought. Both daytime (maximum) and overnight (minimum) temperatures across the state continue to increase (Figure 3).
The increasing frequency and duration of these higher temperatures can increase water stress in trees. Tree stress can be exacerbated when low precipitation accompanies high temperatures. Water stress can kill or weaken trees and increase the likelihood of tree mortality from insects (such as native mountain pine or Douglas-fir beetles) and some pathogens.
Precipitation and drought
Droughts have always been a part of Oregon’s climate. During 18 of the 24 water years from 2000 through 2023, Oregon’s water year (October–September) precipitation was below average relative to 1901–2000 (Figure 4).
The Standardized Precipitation Evapotranspiration Index, which accounts for both precipitation and evapotranspiration, shows that at the statewide level, extreme droughts occurred periodically from 1896 through 2023, with prolonged drought through the majority of the periods 1924–1938 and 1987–1993 (Figure 5).
What does climate change portend for precipitation and drought in Oregon? Throughout the 21st century, annual average precipitation is expected to increase slightly relative to the historical period (1950–2014) (Figures 1, 6), particularly in winter. Over the period 1950–2100, snowfall is projected to decrease by no less than 50% in all major ecosystems in Oregon. The proportion of precipitation falling as rain may increase by 30%–50% over much of Southeastern Oregon and by 3%–10% in Western and Coastal Oregon.
Given projected changes in both temperature and precipitation, annual drought risk likely will increase over the 21st century on the western slopes of the Cascade Range and the southern Coast Range, decrease in the Deschutes and John Day basins in north-central Oregon and change little elsewhere.
Summer precipitation is expected to decrease, and drought risk during summer is likely to increase statewide.
Potential effects of climate change on your land
How might climate change affect the management of forests and other ecosystems on your property? Part of the answer depends on whether your property is becoming drier, the extent to which local temperatures are increasing and the tree species or genotypes that are present.
Tree species that are more sensitive to moisture availability and temperature, such as shade-tolerant western hemlock and western redcedar, may be more likely to be negatively affected if your area is becoming warmer and drier.
If your forest is dominated by Douglas-fir trees on south-facing (warm) slopes, on soils with limited water storage capacity or on ridges where trees are more exposed, growth of the trees may decline, and pockets of tree mortality may develop as the climate warms. Therefore, it may be necessary to plant different tree species or genotypes after a timber harvest, or change the extent to which you thin trees and which species you retain in your forest. It may mean a shift away from Douglas-fir or maintaining lower tree densities. Other fact sheets in this series cover these concepts in more detail.
Summary
Oregon’s climate is changing, and the changes will affect vegetation across the state and on your property. There is overwhelming scientific consensus that temperatures will continue to rise, increasing water demand and water stress on trees and other vegetation. The degree to which water demand and stress increase will vary across the state and among species. Some forests will decline or change as species’ habitats shift across the landscape.
Given that trees are long-lived, the management decisions you make today may increase the resilience of trees on your property to projected changes in climate. What can you do to prepare? First, observe what is happening on your property. Are you seeing areas where trees are dying or appear stressed, and do particular species appear more stressed than others?
You may want to consult with an Extension or Oregon Department of Forestry professional about your observations. See Forests in a changing climate: A framework for management, EM 9535, for information on how to approach climate resilience in your forest. The other fact sheets in this series provide information on managing existing stands, reforestation and other topics in the face of climate change.
References
- Fleishman, E., editor. 2025. Seventh Oregon climate assessment. Oregon Climate Change Research Institute, Oregon State University, Corvallis, Oregon.
- O’Neill, L.W., M. Koszuta, N. Siler and E. Fleishman. 2025. Oregon drought history and twenty-first century projections. Pages 94–114 in E. Fleishman, editor. Seventh Oregon climate assessment. Oregon Climate Change Research Institute, Oregon State University, Corvallis, Oregon.
- Pierce, D.W., and D.A. Cayan. 2025. Projected changes in Oregon precipitation. Pages 54-78 in E. Fleishman, editor. Seventh Oregon climate assessment. Oregon Climate Change Research Institute, Oregon State University, Corvallis, Oregon.
This series was supported by an agreement with and technical contributions from the USDA Northwest Climate Hub.
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