According to a new United States Department of Agriculture (USDA) plant hardiness zone map released in November 2023, parts of lower Eaton Canyon have been elevated to the 10b zone classification. The USDA 10b zone is characterized by annual average extreme minimum temperatures being within 35°F and 40°F. In other words, the average year is not expected to drop below 35°F even on the coldest winter nights in 10b zones.
This warming is a direct result of the combination of the urban heat island (UHI) of Los Angeles and global climate change.
The USDA plant hardiness zone map is a reference that can be used by gardeners to understand which of the plants they wish to grow can survive the coldest temperatures of the year. Since it is based solely on the year’s minimum temperature, the map has been criticized for its inability to incorporate other aspects of a particular area’s climate. For example, most of Miami-Dade County in southern Florida shares a USDA hardiness zone of 10b with Eaton Canyon. This is because Eaton Canyon and Miami-Dade County both see an average annual extreme minimum temperature of 35°F – 40°F. While Miami-Dade County is a warm tropical rainforest that has never exceeded 100°F, Eaton Canyon has a relatively cooler mediterranean climate that can top 115°F in summer.
Being located in a dry, mountainous region of the world, Eaton Canyon is subject to dramatic temperature swings between the ridgetops and the canyons at night. On dry winter nights, these temperature differences can be most pronounced. Here, temperatures within the wash can plunge into the 30s while the homes overlooking the canyon remain in the 40s. A given night’s minimum temperature can be as much as 15°F warmer at the Pinecrest Gate compared to the Eaton Canyon Nature Center. At a more microclimate scale than just broader Eaton Canyon, it’s possible that some areas are already in USDA hardiness zone 11a, which does not drop below 40°F on even the coldest nights of winter.
Here is a look at how annual extreme minimum temperatures have warmed locally over the past 116 years:
