DC area tree pollen is on the rise due to unusually warm weather

Among all the wonderful aspects of spring, tree pollen is the microscopic bug that often makes life miserable for allergy sufferers. This year, unusually warm weather has pushed average tree pollen counts in the DC area to near-record levels.

The numbers have already climbed to the high limit in eight days this year. So far, the highest daily count was 1,171 pollen grains per cubic meter of air measured in early March. But that number will likely be surpassed in the coming days and weeks.

Washington has had an unusually early spring this year with above-average temperatures Sixth-hottest record Year to day. Plant and tree life, including the Tidal Basin's famous cherry blossoms, are rapidly going into spring mode.

As temperatures rise driven by human-caused climate change, the early arrival of spring and the rapid onset of allergy season have become common in recent years.

The first tree pollen grains of 2024 were counted within 10 days of the year. By late January, numbers were above average and climbing. Aside from a short-term cold snap or two, the late winter pollen season roars on — a common theme in recent years.

Moderate tree pollen levels were first observed on February 8, a week earlier than normal; February 22nd is marked as a high pollen day. A pollen count of at least 15 grains per cubic meter of air is considered moderate; High starts at 90 grains.

During the fourth week of February, the average count was 522, compared with an average of 75 grains, Susan Kosisky, director of aerobiological reporting and evaluation at the U.S. Army's Centralized Allergy Extract Laboratory, said in an email.

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The last week of February and the first week of March both recorded the second-highest average numbers, Kosisky said.

This year's figure is still short of 1,500 grains, which is considered “very high,” but the average first date — April 8 — has been rising in recent years. Every year since 2020, this has occurred before this date.

Last year, the first high number occurred on February 23 – the previous year on record – and March 6 the year before that.

Much of this early flowering is tied to temperature, especially in winter and early spring. Because this year was so mild, some tree species did not go completely dormant as expected.

This winter, every month from December to February has been 2 to 4 degrees above normal, while very few night frosts have been reported. In late January, temperatures soared to 80 degrees, and five days in February saw highs in the 60s.

“Very warm days (especially in the 60s to 70s) in our region in mid-January will stir the trees and release their pollen,” Kosiski said.

Washington's average temperature has risen About 0.3 degrees per decade Since 1900 only in winter A little less quickly in March.

Both increased temperatures and increased carbon dioxide levels in the atmosphere due to the burning of fossil fuels can increase pollen levels. A study published in 2020 found that The pollen season has expanded by several weeks and has increased by double-digit percentages across North America since the late 1900s.

There is more pollen to come

The average date of peak tree pollen in the Washington region is April 14, or a month off.

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Last year, despite a very warm winter and a big pollen spike in late February, the peak occurred on April 13; Different tree species release their pollen at different times, and some years may have multiple peaks. From 2020 to 2022, the peak has already occurred. While peaking early in the season, sometimes there is less pollen because only the trees are excreting.

“Typically, if there's a high production of tree pollen in March, then April is actually low,” Kosisky said.

After a big burst of pollen during the hottest March on record in 2012, counts were on the low side for the rest of the season, Kosisky said.

The average peak value was 2,516 grains, or more than double this year's peak. Last year, its value was 3,319 grains. Peaks have exceeded 4,000 twice in the past two decades; It reached 4,539 grains on April 25, 2009 and 4,147 grains on April 6, 2010.

It's too early to know if this year's fast start and possible early peak means the second half of the season will be cut short — tree pollen typically fades by early May.

“Predicting future pollen counts for the season is a challenge because of the year-to-year (and week-to-week) variability in temperature, humidity, and precipitation,” Kosisky said. “Tree species may have intrinsic cycling patterns where large amounts of pollen are released and have multiple years.”

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