Climate Change

In the Sugar Bowl portion of Redwood Mountain Grove in Kings Canyon National Park, scorched sequoias stand as a testament to the profound impacts of warming climate, fuel buildup, and increasing fire severity. The KNP Complex Fire that burned this grove ignited from lightning in September 2021, and reached a size of 90,000 acres, with most of the acreage within these parks.

NPS Photo - Linda Mutch

 

If you have visited or heard stories of giant sequoias, you would probably never imagine that so many groves across the Sierra Nevada would burn severely in our lifetimes. After all, giant sequoias are icons of resilience, adapted to survive thousands of years in a landscape that regularly burned. Now, a warming climate combined with increased tree densities, and the buildup of sticks and logs from decades without fire in many forests, are increasing wildfire across the western U.S. In 2020-2021 alone, scientists estimate that wildfires killed 13-19% of the world's large sequoias.

Impacts from human-caused climate change are evident in these parks. Temperature is increasing, snowmelt occurs earlier, droughts are more severe, and tree mortality has dramatically increased. This page highlights changes we have already seen and may expect to see in future years, and provides links to more information.

 

An increasing trend in temperature (top graph) and lack of a trend in precipitation (lower graph) shown for 1940-2019. These graphs were developed from data collected at 3 mid-elevation park weather stations (6319 to 6703 feet), representative of where giant sequoia/mixed conifer forests grow.

Graphs developed by the National Park Service from a recently published climate dataset (Kim and Grulke 2022)

Warmer Temperatures and Hotter Droughts

Trends of warming temperatures have occurred over the last half century in the Sierra Nevada mountain range, at least partly in response to increasing greenhouse gas concentrations in the atmosphere. While precipitation has not shown a notable trend in this time period, recent hotter drought has had profound impacts, killing many trees in these parks and across the region.

Temperature affects water availability and what type of precipitation falls. In hotter droughts (as occurred in 2012-2016), unusually high temperatures worsen the effects of low precipitation, resulting in greater water loss from trees and lower water availability. Warming temperatures affect the amount of precipitation that falls as rain versus snow.

By the end of the century, temperatures in the Sierra Nevada are projected to warm by 6 to 10°F on average, enough to raise the divide between rain and snow during a storm by about 1500 to 3000 feet. Future precipitation totals are not expected to increase or decrease more than 10 to15% compared to past and current levels. But precipitation extremes (both as deluge and drought) are projected to increase substantially.

 

Shrinking Snowpack and Glaciers

 

Compare Recent Years of Average and Record Low Snowpacks

Left image
Satellite image of the Sierra Nevada mountains, California, and western Nevada, March 27, 2010, a year with average  snowpack.
Credit: Moderate Resolution Imaging Spectroradiometer (MODIS), Aqua Satellite, NASA

Right image
Satellite image of the Sierra Nevada mountains, California and western Nevada, March 29, 2015, a year with the lowest average snowpack on record. Note that most of the white in the right side of image is cloud cover in Nevada.
Credit: Moderate Resolution Imaging Spectroradiometer (MODIS), Aqua Satellite, NASA

The landscape change is stark between 2010 (a year of average snowfall) and 2015, the lowest snowpack year on record. In the photos, two major river drainages in Sequoia and Kings Canyon National Parks are shown - the Kaweah and the Kings. Low snowpack reduces the amount of water available in the parks as well as how much rivers carry downstream to reservoirs that help supply water to farms and communities.

 

Water flowing in the Marble Fork of the Kaweah River in Sequoia National Park, with snow at the edges that will melt into the water as temperatures warm.

Photo courtesy of Karen Franzen Acurso

About 60% of California’s fresh water (and 75% of its agricultural water) comes from the Sierra Nevada snowpack. This reservoir of frozen water stored in the mountains gradually melts in the spring and summer, providing water to park ecosystems and regional communities, industries, and farms during the dry summer season. Even though average annual precipitation is not expected to change substantially, the Sierra Nevada snowpack is declining in response to warming. Higher temperatures reduce the area where snow occurs by raising the elevation where it is cold enough to snow. Warming temperatures also cause earlier snowmelt so that snowpacks do not accumulate or persist as long into the dry season. In a place where snowmelt drives water availability, loss of snow over large areas will affect where plants and animals can live and how communities conserve and use more limited water supplies.

Sierra Nevada glaciers have shrunk by 55 percent between the early 1900s and 2004 due to increasing spring temperatures, reducing a source of late summer and fall meltwater for local wetlands, streams, plants, and animals.

 

On October 4, 2021, a large smoke column from the KNP Complex Fire rises from mixed-conifer forest in Kings Canyon National Park.

NPS Photo - Joe Suarez

Larger and More Severe Fires

Fire plays an important role in Sierra Nevada ecosystems. Periodic fires cycle nutrients and reduce the density of trees as well as the amount of sticks and logs on the ground (fuels). Some species, such as giant sequoias, rely on fire to reproduce – fire increases seed release, exposes mineral soil, and creates sunny gaps between trees where seedlings can grow. But in recent decades, fires across the western U.S. have become larger, more frequent, and more severe (damaging to plants and soil). Why? Both fuel buildup from lack of recent fire as well as warming climate trends create conditions ripe for large, longer-lasting, and more severe fires.

From 2015 to 2021, six fires have killed unprecedented numbers of large sequoias (see map below for locations of fires and groves). Over 85 percent of all giant sequoia grove acreage across the Sierra Nevada range burned in these fires, compared to only one-quarter in the preceding century. Scientists estimate that the 2020-2021 fires are likely to have killed 13-19% of the world's large sequoias. For more details about the estimated loss of giant sequoias in the 2021 KNP Complex Fire, see this web summary. In addition to loss of sequoias, many pines, firs, and incense-cedars died in these fires.

Sequoia and Kings Canyon initiated prescribed burning in 1968 as a tool to restore fire as an ecosystem process and continue to manage fire for ecological benefit while reducing threats to human health, safety, and property.

 

Footprints of six fires that significantly impacted giant sequoia groves - Rough Fire (2015), Railroad and Pier (both 2017), Castle (2020), and KNP Complex and Windy (both in 2021). Giant sequoia groves in or near the fires are shown in red.

NPS - Joshua Flickinger

 

View from the edge of Giant Forest of mixed-conifer forest with many trees showing brown needles - these trees died during the 2012-2016 severe drought.

USGS photo - Nate Stephenson

Effects on Forests

Regional warming is implicated in the near doubling of annual tree-mortality rates measured in Sequoia National Park between 1983 and 2004. During the severe drought from 2012 to 2016, large numbers of trees died across the Sierra Nevada, particularly at lower elevations between 5,000 to 6,000 feet. This drought was severe because it was a “hotter drought”. Trees were already stressed from low levels of precipitation. Higher temperatures cause increased water loss from trees, further reducing the water available for growth, reproduction, and resisting bark beetle attacks. Acute drought stress combined with bark beetle attacks resulted in greatly elevated mortality for several common tree species – ponderosa pine, sugar pine, incense-cedar, and white fir. Read more about climate change impacts on our Forest Health and Climate Change page. During this hotter drought, scientists documented beetle kill of giant sequoias for the first time. Learn more on the Giant Sequoias and Climate page.

A combination of warming climate, very dry conditions, and high levels of tree densities and fuels has resulted in severe wildfires between 2015 and 2021, killing many trees in these parks and other Sierra Nevada forests. Park managers and scientists are adapting forest management practices in response to these unprecedented changes. To learn more about climate change impacts to forests, visit our Forest Health and Climate Change page.

During this hotter drought, scientists documented beetle kill of giant sequoias for the first time. Learn more on the Giant Sequoias and Climate page.

 

Upper photo - California Spotted Owl; center photo - Pacific fisher; and lower photo - mountain yellow-legged frog.

Owl photo by Julio Mulero, Flickr 2.0 Generic (CC BY-NC-ND 2.0P; Pacific fisher photo by US Forest Service Pacific Southwest Research Station, Flickr, 2.0 Generic (CC BY 2.0) and mountain yellow-legged frog courtesy of Isaac Chellman.

Effects on Wildlife

By affecting vegetation condition, temperature, and water availability, climate change affects the geographic ranges of some animals, or the areas where they can live. It can also affect animal physiology, or how well their bodies and life cycles of growth and reproduction function.

Changes in Geographic Ranges

If the lower elevations or latitudes of a species range deteriorate due to warming temperature or other impacts, some animals may shift their range upward where conditions are more favorable. Range shifts have been documented for numerous Sierra Nevada species over the past century. Research comparing historic (1914-1920) and recent wildlife surveys in Yosemite found that:

1. Elevation limits of geographic ranges primarily shifted upwards.
2. Several high-elevation species (such as alpine chipmunk) had range contraction (shifted lower elevation limits of geographic ranges upward).
3. Several low-elevation species expanded their range upslope.

Impacts on Animal Physiology

While it may be difficult to detect direct effects of climate change on wildlife, reductions may occur in reproduction and survival. These would eventually be reflected in population or species declines.

Examples of animals that may be vulnerable to these kinds of impacts include species already in decline that specialize in habitats like old growth forests or small, fishless lakes and ponds. Old growth forests are home to California spotted owls and Pacific fishers. A combination of drought, high temperatures, and large, high-severity wildfires may all contribute to tree mortality and decline of old-growth forests.

Mountain yellow-legged frogs are listed as Endangered under the federal Endangered Species Act. Their decline is linked to the introduction of non-native trout that prey on frog tadpoles into Sierra Nevada lakes and a fungal disease that causes most infected frogs to die. Adding climate change to this mix causes increased summer drying of breeding lakes from reduced snowpack, leading to less breeding success and greater vulnerability to disease.

 

Responding to Climate Change

Climate change affects national parks across the country. The National Park Service (NPS) Climate Change Response Strategy provides direction to address the impacts of climate change. The following four components guide our actions: science, mitigation, adaptation, and communication. How we move forward in this time of rapid change is up to each of us, at all levels of the NPS, and as individuals who cherish national parks and the communities where we live.

Science

Collaborate with others to conduct research and assess vulnerability of species and landscapes to climate change. Learn from and apply the best available climate change science. One example of this in these parks is giant sequoia research to better understand these trees’ vulnerability to climate change and severe fire. Learn more: Giant Sequoias and Climate.

 

A firefighter uses a drip torch to ignite a prescribed burn in Giant Forest, 2011.

NPS photo - Tony Caprio

Mitigation

Reduce the carbon footprint of the NPS. Promote energy efficient practices, such as alternative transportation. The parks’ shuttle system offers an alternative way to travel to and within Sequoia National Park during the summer season. Enhance carbon sequestration as an ecosystem service. Lands within the National Park System play an important role in reducing climate-related damages by sequestering (taking up and storing) CO₂, a major greenhouse gas. In years with large wildfires, some areas may release more carbon than they store. Managing forests to be more resilient to wildfires and warming climate also makes them better able to sequester CO_2. What actions can we take to reduce our personal carbon footprints?

Adaptation

Adapt approaches for managing natural and cultural resources and park infrastructure under a changing climate. Determine which resources or infrastructure are most at-risk. Examples include prioritizing where to invest effort in making landscapes more resilient to fire (such as conducting manual thinning or prescribed burning) or making infrastructure like bridges and roads better able to withstand extreme precipitation and flood events. How can our communities adapt to increased risk of extreme weather events or wildfires?

The resist-accept-direct (RAD) approach helps decision makers make informed and strategic choices. One can respond to change by:

• Resisting (working to maintain or restore based upon historical or acceptable current ecosystem conditions)
• Accepting (allowing an ecosystem to change without intervening)
• Directing (actively shaping ecosystem change toward preferred new conditions)

Learn more about the resist-accept-direct framework.

 

Communication

Communicate effectively about climate change and its impacts. Learn about the science of climate change and decision tools for coping with change. By sharing our stories of change or loss we experience in places we love, we can all increase understanding of climate change impacts and heighten the urgency for reducing greenhouse gas emissions.

 

Learn More

Visit the links below to learn more about how climate change affects glaciers; snowpack and rivers; and fire severity, giant sequoias, and forest heatlh in these parks. You can also explore the NPS Climate Change web page to learn more about how national parks across the country are addressing the challenges of climate change.

 

 

References

Basagic, H.J. and Fountain, A.G., 2011: Quantifying 20th Century Glacier Change in the Sierra Nevada, California. Arctic, Antarctic, and Alpine Research, 43(3): 317-330.

Das, A. J., and N. L. Stephenson. 2013. A natural resource condition assessment for Sequoia and Kings Canyon National Parks: Appendix 22 – climatic change. Natural Resource Report NPS/SEKI/NRR—2013/665.22. National Park Service, Fort Collins, Colorado.

Dettinger, M., H. Alpert, J. Battles, J. Kusel, H. Safford, D. Fougeres, C. Knight, L. Miller, S. Sawyer. 2018. Sierra Nevada Summary Report. California’s Fourth Climate Change Assessment. Publication number: SUM-CCCA4-2018-004.

Kim, Y. and N. E. Grulke. 2022. 80-year meteorological record and drought indices for Sequoia National Park and Sequoia National Monument, CA. Fort Collins, CO: Forest Service Research Data Archive.

Shive, K., C. Brigham, T. Caprio, and P. Hardwick. 2021. 2021 fire season impacts to giant sequoias. NPS web article.

Stephenson, N. and C. Brigham. 2020. Preliminary estimates of sequoia mortality in the 2020 Castle Fire. NPS web article.