The West's more flammable nights
- Andrew Freedman, author of Axios Generate
Changes in the number of nighttime hours that burnable land spent above a threshold of an index known as the vapor pressure demand. Map: Balch et al., Nature
A new study found that the West is experiencing an increasing occurrence of hot, dry nights that are contributing to more intense wildfires.
Why it matters: The trends identified in the study, published in the journal Nature, mean that wildfires are able to grow larger and destroy more structures than they used to. It also means less rest for firefighters.
Zoom in: The researchers found there are now about 11 more flammable nights every year in the West compared with 1979, a 45% increase in four decades.
- This trend is largely driven by human-caused climate change, which is causing nights to warm faster than days.
- It is also causing the West to turn drier overall, particularly in the Southwest.
Between the lines: The study examined changes in a metric called the vapor pressure deficit, which captures how primed the air and land are for burning.
- They also analyzed satellite imagery for about 82,000 fires to find a threshold value, beyond which intense nighttime fires can be supported.
- They found a 36% increase in annual average flammable nighttime hours between 1979 and 2020.
What they found: The study shows nighttime fires increased in intensity by 7.2% from 2003 to 2020 globally. But in the West, that figure is 28%.
What they're saying: “Night is the critical time for slowing a speeding fire—and wildfire’s night brakes are failing,” said study lead author and the University of Colorado climate scientist Jennifer Balch in a statement.
Go deeper ... Southwest megadrought: Last 2 decades were driest in 1,200 years