Jul 7, 2023 - News

Mosquitoes are swarming Portland this summer

Data: Climate Central; Chart: Axios Visuals

Mosquito season arrived early this year after a wet spring and a warm start to summer allowed populations along the Columbia and Willamette rivers to skyrocket.

Driving the news: Portland has an average of 129 "mosquito days" — that is, those with the hot and humid weather they crave — per year, Axios' Alex Fitzpatrick and Kavya Beheraj report.

  • The analysis comes from a new report from nonprofit climate science research organization Climate Central, which defines a "mosquito day" as one with average relative humidity of 42% or higher, plus daily temperatures of 50° to 95°.

Why it matters: Mosquitoes are more than just a nuisance — they're a public health threat, carrying diseases such as malaria, West Nile, Zika and more.

The big picture: Between 1979 and 2022, 71% of the 242 locations Climate Central analyzed saw an increase in mosquito days — about 16 days on average.

  • In 2022, Portland saw 128 mosquito days, the same number as in 1979.
  • However, this summer is providing ideal breeding conditions.

State of play: According to Multnomah County Vector Control, the region saw more than five times as many mosquitoes in June as it normally does, thanks to rapid snowmelt from unexpectedly high temperatures in recent months.

  • In the Pacific Northwest, floodwater mosquitoes breed in shallow, damp riverbeds. When those riverbeds swell due to snowmelt or heavy rain, eggs start hatching.

Meira's thought bubble: As someone who is popular among mosquitoes, I've found that wearing long-sleeved, loose-fitting clothing and keeping a diffuser repellent (this is the one I use) nearby does the trick to avoid bites when I want to sit out on the patio at night.

What's next: Experimental efforts to control mosquito populations by releasing genetically modified versions of the insects into the wild are underway in Florida and elsewhere.

  • Those projects, however, are controversial among some locals and skeptics who view them as tampering with the natural ecosystem.

The bottom line: Mosquitoes — and the diseases they sometimes carry — have yet another climate-related problem for many local officials to worry about.

  • Vector Control will treat uninhabited areas of the county's wetlands for mosquitoes using an insecticide, which prevents hatching, via helicopter throughout August.
  • But if this current stint of hot, dry weather continues, mosquito populations could start to decline.
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