Jul 21, 2023 - News

Salt Lake's bad mosquito year could be a one-off

Data: Climate Central; Chart: Axios Visuals
Data: Climate Central; Chart: Axios Visuals

Utah's record-breaking winter may have worsened Salt Lake's mosquito scourge this summer — but in the long run, temperatures here are becoming less accommodating to nature's deadliest pests.

What's happening: The number of "mosquito days" — those with the hot and humid weather the flying insects crave — has trended downward in Salt Lake City over the past several decades, per a new analysis, Axios' Alex Fitzpatrick and Kavya Beheraj report.

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

By the numbers: Salt Lake City was trending toward 23.7 mosquito days in 2022, almost 18 days fewer than in the late 1970s — a decrease of 43%.

Yes, but: Utah's wet year has made this summer abnormally accommodating to mosquitos, with some urban traps catching more than four times the average number of mosquitoes for the past five years on July 1, according to data from the Salt Lake County Mosquito Abatement District.

Chart shows mosquito trap results from May 1 through July 1; As of July 1, 2023 just under 500 mosquitos were found; 5-year averages are about 100 for that date.
Chart via Salt Lake County Mosquito Abatement District

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 latest: West Nile virus was found this week in mosquitos in Davis and Uintah counties.

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

Yes, but: Some locations — particularly in the South — are actually getting too hot for mosquitoes, the analysis notes.

  • They don't thrive in temperatures above 95° F — an increasingly common reading.

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