New climate data analyzed by NOAA shows that during July when the fire season in the West is typically nearing its maximum, the temperatures in the 11 Western states have been rising in recent years. The data from the last 10 years also indicates the amount of precipitation in the Northwest has decreased significantly.
Every 10 years NOAA recalculates the U.S. Climate Normals for the previous 30-year period. Normals act both as a ruler to compare today’s weather and tomorrow’s forecast, and as a predictor of conditions in the near future. They consist of annual/seasonal, monthly, daily, and hourly averages and statistics of temperature, precipitation, and other climatological variables from almost 15,000 U.S. weather stations.
The new annual mean data for 1991 through 2020 shows that most of the U.S. was warmer, and the eastern two-thirds of the contiguous U.S. was wetter, from 1991–2020 than the previous normals period, 1981–2010. The Southwest was considerably drier on an annual basis, while the central northern U.S. has cooled somewhat.
The weather in July has a direct effect on the number of acres burned in Western wildfires. The new data shows the Northwest is considerably drier as a percentage of the previous normal during what is already a dry season.
The rest of the West is pockmarked with wetter and drier zones. The eastern two-thirds of the U.S. has an indistinct pattern of changes in the precipitation normals. Most of the East also remained near the same temperature levels, except for persistent cooling in the north central U.S. and warming in the Northeast. However, the entire West and lee of the Rocky Mountains and Texas are all considerably (up to 2°) warmer.
This warming and drying trend in the West shows up in wildfire activity. The number of acres burned in the U.S. in 2020 — 9,941,167 (not counting Alaska) — was the highest ever recorded since reliable statistics have been available beginning in 1960.
The average fire size by decade is striking, increasing by about 400 percent from the 1980s to the 2010s. Some of that increase could be from the tendency of the U.S. Forest Service and other federal agencies to allow some fires to spread without an aggressive full suppression strategy, allowing an unplanned wildfire to accomplish fuel reduction targets and other objectives. They can do this by using virtually unlimited fire suppression funds and without having to bother with pesky steps like conventional project funding, planning documents, approvals, public input, and environmental compliance required by the National Environmental Policy Act.
