Washington, District of Columbia 2021-08-05 11:41:37 –
August 5, 2021
Firefighters reported that a western wildfire started early in the morning and extinguished late at night, hampering its ability to recover and reorganize before the next day’s relapse.
Studies by scientists at the University of Washington and the US Forest Office show why. Nighttime air drying power has increased dramatically over the last 40 years in many parts of the western United States. NS paper Published online in July in the American Geophysical Union journal Geophysical Research Letters.
“Night is an important time in fire management. When the fire goes out at night, firefighters are given the opportunity to take a break, move equipment and develop strategies. The problem reported by firefighters is nighttime fires. It’s an unexpected increase in activity, “said the lead author. Andy KiodiUW Research Scientist at the Institute for Climate, Ocean and Ecosystem Studies, a joint center with the US National Oceanic and Atmospheric Administration. “Our findings confirm that this has been going on for many, if not all, of the western United States for the past 40 years.”
The atmosphere of the earth is warming due to climate change, and it is warming in many places at night.Suspected to be caused by warm night air Change the daily pattern of wildfire activity, Burns last until late at night.
However, new research shows that not only is the night air warm, but its drying power, the amount of water that the night air can carry away from fuel, has changed dramatically in much of the western United States. increase. This change is not captured in climate models, and the authors state that it may be related to the long-term cycle of nature rather than climate change.
“We pay special attention to recent changes compared to the situation seen in the 1980s and 1990s, when many of today’s firefighters began their careers, and perhaps how normal fire behavior would be. I formed an idea of what to see, “said Kiodi. “We tried to quantify the changes we were hearing from firefighters.”
This study looks at “insufficient vapor pressure,” that is, the difference between the moisture in the air and the saturated moisture level at that temperature. This difference is a measure of the drying power of the air.
“In the southern Sierra Nevada, the average nighttime vapor pressure deficit in the last decade was 50% higher than the average in the 1980s and 1990s,” Chiodi said. “I was surprised. It’s rare to see geophysical data changing so dramatically.”
Part of this change in vapor pressure deficiency occurs because the warmer nighttime air caused by climate change produces higher saturation values. However, due to the low moisture content of the nighttime air in some areas, some of the desiccation power is generated, the effects of which, at least this alone, or in this pattern, are unpredictable in climate change models. The authors have discovered the potential for association with the Pacific Decadal Oscillation, a long cycle that can affect inland weather.
Increased air dryness at night is especially noticeable in the San Fernando Valley of California and the Bitterroute Blue Mountains region, which includes parts of the Idaho Panhandle, southeastern Washington, northeastern Oregon, and western Montana.
“For some years, firefighters have said they feel the fire burns later than before,” the co-author said. Brian Potter At the Pacific Wildlife Fire Science Institute of the US Forest Department. “In some areas, we found that the amount of water in the air was reduced and doubled on warm nights. These, including where the Snake River Complex and Rick Creek fires are currently burning. In the area, fires are much more likely to occur until late at night. “
The analysis used hourly weather output from the European Center for Medium-Range Weather Forecast. The recently released hourly reconstruction of past weather has made it possible to investigate daily cycles.
According to Chiodi, the next step is to further investigate the causes of these changes in nighttime vapor pressure deficiencies. He then wants to link atmospheric conditions more directly to fuel moisture and fire behavior.
Other co-authors Nara Simhan’Sim’Larkin At the Pacific Wildlife Fire Science Institute at the US Forest Department in Seattle. This study was funded by the US Forest Department. AirFire According to the research team and NOAA.
Dryer, warmer night air is making some Western wildfires more active at night Source link Dryer, warmer night air is making some Western wildfires more active at night