Hotter Nights in Northwest as Heat Waves Rise in the Region

In Western Oregon and Washington, the number of heat waves at night is rising, a new study found. Researchers said that people living in these regions must consider buying a fan or an air conditioner as temperatures might soar in the last week of July.

Night-time heat waves occur when the low temperature of the day falls within one percent of the record temperature for at least three consecutive nights.

In July 2009, a heat wave in Seattle broke temperature records dating back to 1891. This heat wave caused even hotter nights that lasted for eight consecutive nights; the longest ever stretch of hot nights in the region. Researchers tried to find out how this record-setting heat wave occurred when compared to other heat waves in the region

The present study was based on temperature records from 1901 to 2009 in the west of the Cascade Mountains in Washington and Oregon. They looked for readings where the night-time low temperatures or daytime high temperatures for three consecutive nights fell within one percent of the readings.

Researchers found about four events of heat waves at night in this region between 1901 and 1980. Generally, cool breeze from the ocean brings down the temperature at night, The Seattle Times reported.

The number of night-time heat waves quadrupled to 12 after 1980, they found.

The study by researchers from The University of Washington is published in the Journal of Applied Meteorology and Climatology.

"In general, minimum daily temperatures have been warming faster than maximum temperatures, so we're not surprised to see a trend in the minimum events," said Karin Bumbaco, at the Joint Institute for the Study of the Atmosphere and Ocean, according to a news release. "Still, we were surprised to see this significant increase in the frequency of nighttime heat waves."

Experts have an explanation for this trend. According to them, high humidity in the region is acting as a blanket, further increasing the effect of heat waves from the Pacific Northwest.

Their study has shown that climate change will lead to nights getting hotter in the region. However, researchers can't say whether or daytime temperatures will be affected by climate change.

The number of hospitalizations due to heat waves also increased by 50 percent on days when there were heat waves, the scientists found.