As storms pummel Hawaii, the Western U.S. continues to bake amid record-breaking heat wave

Communities across the Western United States are in for another week
of unusually high temperatures amid an ongoing and historic early-season
heat wave. It has broken March temperature records in nearly 180 cities, including Phoenix, which hit 105 degrees Fahrenheit last Thursday. 

The National Weather Service forecasts more than 200 record-high
temperatures this week, as the heat wave blankets portions of
California, the Southwest, the central Great Basin, the central/southern
Plains and mid-lower Mississippi Valley. A new rapid attribution study found the weather event would have been “virtually impossible without climate change.” 

I know I sound like a broken record talking about records breaking.
But the anomalous weather poses profound risks to snowpack and water
availability out West, which experts warn could be critically low this
spring. Meanwhile, copious rain in Hawaii is triggering widespread
flooding, crop losses and damage throughout the islands.

Western heat wave’s climate connection 

The Western heat wave was largely caused by a high-pressure system trapping heat from unusually warm Pacific Ocean waters, bringing temperatures 25 to 35 degrees Fahrenheit higher than normal in some areas. 

A study published Friday
by the research group World Weather Attribution found that human-caused
climate change has made this kind of heat wave about four times more
likely to occur over the last decade. 

The researchers used weather records, forecasts and climate models to
compare how these types of heat waves changed under the current rate of
global warming, 1.3 degrees since pre-industrial times. They noted the
affected Western region is warming much faster than many other parts of
the world. 

“These findings leave no room for doubt. Climate change is pushing
weather into extremes that would have been unthinkable in a
preindustrial world,” co-author Friederike Otto, a climate science
professor at Imperial College London, said in a statement.

The study points out that heat waves outside the “traditional summer
period” heighten health risks: People are not yet acclimatized and
seasonal response measures, such as cooling centers, may not be fully
operational. Rachel White, an atmospheric scientist at the University of
British Columbia who was not involved in the study, told Eos that more extensive analysis will be needed to determine climate change’s influence with greater certainty. 

“To do this study as quickly as possible, they are using the one
dataset that does include data for very recent days, but the way that it
does that is by including forecast data,” she said in an email to Eos.
“This is a reasonable thing to do if you need to do a study this quickly
(and this is a rapid attribution!), but does come with the caveat that
the exact numbers they are reporting in terms of return period etc. will
likely change as we are able to more carefully analyse observational
data.”

More broadly, the heat wave jeopardizes water availability out West
following a winter with unsettlingly low snowpack levels in many states,
particularly in the snow-fed Colorado River Basin.

Water managers depend on the slow melt of snowpack to supply water to
streams, rivers and reservoirs for irrigation, recreation and drinking
water. As I reported earlier this month,
high temperatures can cause this limited snowpack to melt and evaporate
more quickly. The Colorado Climate Center at Colorado State University reported that the heat took a “major toll” on the state’s snowpack, which sits at 44 percent of average levels. 

Relentless storms soak Hawaii

As the West Coast bakes, communities in Hawaii are struggling against
the state’s worst flooding in more than two decades. Starting in
mid-March, low-pressure systems known as Kona lows have fueled intense,
windy and exceptionally wet storms over the islands, with only brief
reprieves in between. The storms caused widespread flooding across
Oʻahu, which damaged structures, swept cars onto the street and knocked
out power for many locals, Honolulu Civil Beat reports. 

“We’ve been here almost 20 years. … We lost everything,” Oʻahu resident Melanie Lee told CBS News. “My children’s pictures. Just real sentimental stuff. Now it’s like, now where we go from here?” 

Locals and officials were especially worried
that the immense rainfall would overwhelm an aging dam on the Wahiawa
Reservoir in northern Oʻahu as water rose to a record 85.1 feet—just
five feet shy of what the dam could handle. The structure held, but
long-term concerns remain over the dam’s ability to handle water flows
from worsening storms, experts say. 

Rain also hammered parts of Lahaina, particularly susceptible to flooding due to burn scars from the devastating fires that tore through Maui in 2023. As I reported
last summer, wildfires can burn so hot that they cause shifts in soil
that make the ground fairly water-repellent, making flooding more
dangerous. 

Gov. Josh Green estimated on Friday that the storms had already
caused around $1 billion in damage. And more flooding hit over the
weekend. Farmers reported nearly $11 million in losses across the North
Shore of Oʻahu, Maui, Molokaʻi and the Big Island, Honolulu Civil Beat reports.

On Monday, Green said he formally requested that President Donald
Trump issue a major disaster declaration, which could unlock more
resources for recovery. In the meantime, state and local governments
have launched relief efforts, and community members are digging their
way through mud and debris to return home after evacuating last week. 

“The strength of Hawaii is our people,” Green said at a Monday press
conference. “Throughout this storm, we saw neighbors helping neighbors,
communities stepping up and our emergency teams working tirelessly to
keep everyone safe.”