Idaho Statesman
How has climate change hit Boise? What 150 years of weather data tells us
Nicole Blanchard – September 7, 2022
After a scorching August — the hottest ever recorded here — the effects of climate change may feel closer to Boise than ever. And according to local weather statistics, temperatures, precipitation and other environmental factors have shifted noticeably in the last few decades and the 150 years since record-keeping began.
National Weather Service data shows Idaho’s summers are becoming hotter, overnight low temperatures are warming, and the average number of days with temperatures over 100 degrees has more than doubled in the last 30 years.
“It’s a totally different climate than our parents and grandparents grew up in,” Jay Breidenbach, a meteorologist at the Weather Service Boise office, told the Idaho Statesman in a phone interview.
Boise heats up
Breidenbach said scientists tend to look at climate change in 30-year periods. That gives them enough data to detect trends while still measuring the shifts in a way the public can understand.
“It helps us see (climate change) relative to our lives,” Breidenbach told the Statesman.
Data from the last 30 years is telling. The National Weather Service has been keeping weather records in Boise since the 1870s, and records show many of the hottest summers in that period have happened in the past three decades. Every summer in the last decade would make the list of Boise’s 30 hottest summers since the 1870s, Breidenbach said.
This summer is Boise’s second-hottest on record, following last summer, when a record-breaking heat wave hit the Northwest. The average temperature this August was 81.9 degrees — more than 3 degrees hotter than the previous record of 78.7, which was set in 2001. Breidenbach said average temperatures are calculated by taking the sum of each day’s minimum and maximum temperature and dividing it by two.
Numbers from the National Weather Service’s earliest records showed even more temperature shifts. The average annual temperature has risen from 50.3 degrees in the late 1870s to 52.7 in recent years. Average minimum and maximum temperatures have also warmed, meaning Boise’s hottest temperatures are a few degrees hotter, and its coldest temperatures are also toastier.
Breidenbach said extreme hot weather is becoming more common in Boise.
“The number of days each summer with max temperature reaching or exceeding 100 degrees has risen from about six days in 1992 to about 13 days now,” he said in an email to the Statesman.
This summer, Boise reached 100 degrees or hotter 23 times.
Less snow, rain in Boise
Boise has also become drier over the years, data shows. Josh Smith, a meteorologist who focuses on climate change at the Weather Service Boise office, said the temperature and precipitation shifts are linked.
“There is a subtle but noticeable warming that’s affecting precipitation and snowfall,” Smith told the Statesman in a phone interview. “That is really important for our area. We get most of our water from snowfall.”
When record-keeping began, the National Weather Service recorded an average of 13.1 inches of precipitation per year in Boise. By 1992, that number had fallen to around 11.6 inches. In recent years, the average is about 11.2 inches of precipitation annually.
Idaho has been in the midst of a multiyear drought, with nearly 90% of the state experiencing some level of water shortage as of Tuesday, the U.S. Drought Monitor showed.
The drought is due in part to poor snowpack. Weather Service data shows an average of 24.4 inches of snow fell in Boise annually in the late 1800s, but that number has fallen to 18.2 inches of snow on average. Snow depth has also decreased over the years.
How accurate is Boise weather data?
Smith said some Boise residents question the accuracy of the National Weather Service data. The statistics are recorded at the agency’s office, which has changed location over the years.
But Smith said variability caused by change in location is accounted for in the agency’s data, and the office has been around long enough to establish some solid trends.
The meteorologists said the 150 years of data helped show the realities of a changing climate despite the occasional unusual snowstorm or record cold day. Breidenbach said record cold days do still happen, but with much less frequency than new high temperature records.
Smith said the key is to look at the trends.
“When you look at the data without any frame of reference, you could get lost in the variability of each year,” Smith said. “It’s important to look at a larger window of time.”