Snow coverage in the Sierra Nevada is predicted to diminish due to rising temperatures, yet the occurrence of avalanches may stay the same or even rise at higher altitudes. This poses a significant threat to the bighorn sheep population that resides in those regions, based on new findings that will be shared at AGU’s 2024 Annual Meeting.
Snow coverage in the Sierra Nevada is predicted to decrease overall as temperatures rise, but avalanche occurrence may either remain stable or increase at elevated areas. This is troubling news for the bighorn sheep that inhabit these regions, according to new findings set to be presented at AGU’s 2024 Annual Meeting.
In his 1894 book “The Mountains of California,” John Muir extolled the “perfect strength and beauty” of the wild Sierra Nevada bighorn sheep, which he described as “leaping unscathed from crag to crag.” Today, however, these majestic creatures are classified as endangered. After overcoming initial challenges—such as diseases and overgrazing caused by domestic sheep brought by settlers—their population slowly grew from just 100 in 1995 to around 600 in 2015. Unfortunately, this conservation progress is now at risk due to new threats like avalanches. Along with predation from mountain lions, the Sierra bighorn sheep population has declined by half since 2023.
Ned Bair, a researcher from the University of California, Santa Barbara, and his team conducted simulations to assess how avalanches might impact bighorn sheep under current (1990-2020) and future (2050-2080) climate conditions. Their findings indicated that while overall snow coverage in the Sierra Nevada is expected to decrease with climate warming, avalanches that threaten bighorn sheep may persist.
“The snow will certainly diminish in the future, and that’s going to affect the sheep, which are already quite vulnerable,” Bair explained. “During dry winters, they struggle to find enough food, and in heavy snowfall years, they face starvation and threats from avalanches.”
Bair will present his research on Tuesday, December 10, 2024, at AGU’s Annual Meeting in Washington, D.C.
A risky setting for bighorn sheep
While bighorn sheep can be found in other western mountain ranges, the Sierra Nevada subgroup is genetically unique, with only 350 individuals left. The remaining herds inhabit rocky, elevated terrains, feeding on grasses, herbs, and shrubs.
“They prefer living in extremely challenging environments, which explains the issue with avalanches,” Bair noted.
Snow plays a critical role as a water source for bighorn sheep but can also present dangers. The winter of 2022-2023 brought record-setting precipitation to California, resulting in about 18 meters (60 feet) of snow in the Sierra Nevada. That winter, at least 73 bighorn sheep were killed by avalanches, including 12 fatalities from a single avalanche, as reported by the California Department of Fish and Wildlife.
The researchers estimated the amount of snowfall likely to occur across the Sierra Nevada amid future climate changes, utilizing precipitation data from notably dry years (2013 and 2018) and a wet year (2019) to inform their simulations.
Despite forecasting a general reduction of snow cover in the Sierra Nevada, this decrease will primarily affect lower altitudes, where snow may turn to rain. High-altitude areas where bighorn sheep thrive may experience minimal changes in snow cover. In fact, these elevated regions could see an increase in snow accumulation due to climate change intensifying California’s atmospheric rivers, which contributed to the Sierra Nevada’s remarkable snowpack in 2023. More snow could lead to a higher frequency of avalanches in these areas, consequently resulting in more bighorn sheep fatalities.
The response of the California Department of Fish and Wildlife’s Bighorn Sheep Recovery Program, which was initiated following the devastating winter of 2023, to the rising threat of avalanches is still uncertain. Additionally, the wild sheep could face growing hazards from the resurgence of wolf and mountain lion populations.
“Maintaining this population is quite challenging,” Bair acknowledged. “I genuinely worry about the prospects of my children seeing a bighorn sheep in the wild when they reach my age.”
