Winter began in earnest when an atmospheric river drenched Northern California with record breaking rainfall totals and dropped a thick blanket of snow on the Sierra-Cascade at the end of November 2024.
This historic storm followed another record-breaking weather event in 2024—California’s hottest summer ever recorded.
Although it’s too early to know if this year’s winter will bring more record-breaking storms, the fast transition from one extreme weather event to another, known as weather whiplash, is an increasing pattern seen throughout the state.
Wet spring followed by hot summers contributed to Park Fire spread
The burst in vegetation growth from a wet 2024 spring quickly dried out during the heatwaves that followed in June and July. Once the Park Fire ignited, it was able to spread rapidly through the fuel load, making it the fourth largest wildfire in the state’s recorded history.
For the Sierra-Cascade Region, the record-breaking heat is one of many extreme weather events that have defined the past decade.
Since 2013, the Region has also experienced two prolonged severe droughts, which contributed to an unprecedented tree mortality event and multiple record-shattering wildfire seasons typified by large damaging high-severity burns, and a 2022 – 23 winter unlike any in recent memory.
The precipitation rollercoaster
California’s mediterranean climate has natural cycles of wet and dry periods. However, large swings in precipitation are expected to become more severe as temperatures rise due to human-caused climate change. During the 2022 – 23 water year, 31 atmospheric rivers slammed into California resulting in record-breaking snowpack, whereas, just a year prior, the state experienced one of the driest January to March periods on record, deepening a three-year drought.
Bigger swings have bigger implications for the state’s water managers. As noted by Jay Lund, the Vice-Director for the Center for Watershed Sciences, “We are always going to have to worry about floods and droughts in California. If we manage it well, we won’t have to worry as much.”
Warmer temperatures contribute to wildfires in forests primed to burn badly
The pendulum swing from heavy rainfall to hot summer temperatures could make matters worse. Elevated precipitation catalyzes plant growth which, when directly followed by hot temperatures, dries out, leading to heavy and flammable ground and understory fuels, increasing the risk of large high-severity wildfires.
Since 1900, only eight fires have burned more than 200,000 acres in the SNC service area. All of those fires occurred from 2012 – 2024.
Historically, fire swept through most parts of California’s Sierra-Cascade every 20 years or so and burned with a mixture of fire effects.
However, in many parts of the Region it has been more than 100 years since fire has burned through the landscape. This has led to many small trees growing close together and a lot of dead, dry wood on or near the ground. When fires burn through this kind of forest structure, they burn hotter and more severely, creating uncharacteristically large landscapes of dead trees.
Unprecedented tree mortality
Large-scale tree mortality events are mainly driven by abnormally high temperatures and prolonged drought, as scarcity of water strains otherwise healthy trees. The lack of water supply is exacerbated by increased competition among trees located in unnaturally dense forests.
To date, tree mortality has disproportionately impacted large pines in the southern Sierra where more than a quarter of live trees are estimated to have died between 2012-2016. Signs of a new tree mortality event emerged in 2021 and 2022, this time among higher-elevation fir forests in the northern and central Sierra-Cascade.
Investing in resilience can help weather the whiplash
The Smithneck Fuels Reduction Project (left), funded by the Sierra Nevada Conservancy, slowed the progression of the 2024 Bear Fire (right), allowing firefighters to stop the fire and protect the Sierra Brooks community. Credit: US Forest Service.
The dizzying pace of drastic change underscores the need for California to invest in the resilience of Sierra-Cascade communities and landscapes, restoring forest health and economic vitality, so the Region can adapt and thrive in a changing climate.
Healthy ecosystems are intrinsically intertwined with the well-being of communities during hazardous events. For example, meadow and riparian ecosystems act as flood control during large precipitation years by capturing and slowing the release of sediment and water runoff. Forests with diverse age, species, and stand composition have proven to slow wildfires, greatly reduce the severity at which they burn, and decrease the occurrence of tree mortality.
Although forest-restoration projects are shown to be effective at mitigating risk from insects, drought, and wildfire, forest managers often feel outpaced by the additional stress and risk caused by extreme precipitation events, prolonged droughts, and increasing temperatures, all of which are driven by climate change.
The sheer pace of change occurring over the past decades underscores the need to accelerate our efforts to increase landscape and community resilience, as California simultaneously doubles down as a global leader in combatting climate change. It’s how the state can leave healthy, thriving, and forested regions to future generations.