Skip to main content
You are the owner of this article.
You have permission to edit this article.
Dire warnings for Arizona, the Southwest included in new federal climate report
top story

Dire warnings for Arizona, the Southwest included in new federal climate report

More heat and drought. Less water. More heat-related deaths and hospital visits. Bigger wildfires.

Fewer native trees. Maybe more valley fever cases. Someday, possibly less food and less energy, not counting solar energy.

These and other impacts of warmer weather in Arizona and the Southwest are laid out in a chapter of the new federally financed National Climate Assessment devoted to this region. Together, they paint a stark picture of a region facing a wave of sudden and at times overpowering changes.

This Southwest report is more detailed and shows more significant impacts than a similar chapter in the last National Climate Assessment report, from May 2014.

“What we’re seeing is a transition from a climate-related nuisance to a climate-related problem,” said Gregg Garfin, a longtime University of Arizona climatologist and lead author of the new report’s Southwest chapter. “A nuisance you can brush off. But a problem is chronic.”

The Southwest is already the country’s hottest and driest region, with the world’s record high temperature of 134 degrees recorded in Death Valley National Park in California.

Looking regionally, the Southwest’s average annual temperature rose 1.6 degrees between 1901 and 2016, the new report said. In Arizona, the average temperature has risen about 2 degrees since the early 2000s, the National Oceanic and Atmospheric Administration said in a separate report. Pima County’s average annual temperature rose 2.1 degrees from the period 1895-1925 to the period 1987-2017, Garfin said.

When Garfin looks at the hotter weather’s impacts across the region, he sees “very clearly” connections between water, land use, energy, food production and ecosystems.

The drought that crippled California for much of this decade, for instance, reduced not only people’s water supply, but triggered dramatic reductions in crop production, reduced hydroelectric energy generation, damaged ecosystems and much more from major wildfires, and reduced salmon and shellfish production for coastal Indian tribes, Garfin noted.

Here are some specific impacts discussed in the report:

Water. Continued research has led to “very high confidence” that our water supplies have declined, in part because of climate change.

Generally, climate change has significantly altered this region’s entire water cycle, the report said. That includes decreases in snowpack, earlier peaks in spring streamflow and increases in the proportion of rain to snow.

In 2017, a study by former University of Arizona climatologist Jonathan Overpeck and Colorado State University researcher Bradley Udall found climate change triggered a range of 17 percent to 50 percent of reductions in Colorado River flows from 2000 through 2014.

This fall, a new study co-authored by Udall and other researchers concluded that 53 percent of the river’s streamflow decline from 1916 to 2014 was due to warming weather.

In California, higher temperatures aggravated the impacts of the 2011-2016 drought, the vast majority of studies that examined this question have found. In 2014-15, unusually warm weather led to the state’s lowest snowpack on record.

In the Southwest’s Rio Grande Basin, higher temperatures have been linked to 25 percent declines in spring snowpack and slight runoff reductions since 1958.

Today, scientists describe the Southwest’s overall climate trend as “aridification,” said Udall.

Aridification is used to describe a period of transition to an increasingly water-scarce environment, said a paper that Udall and nine other Colorado River researchers wrote earlier this year. While drought is usually seen as temporary, aridity is permanent.

Wildfires. The new climate report cites one of the most sweeping studies of many to link the West’s worsening wildfires with climate change. There’s “high confidence” in this link, and in the fact that climate change has also increased tree deaths and caused shifts of plants and animals northward in Southwest ecosystems.

The wildfire study concluded that the area burned across the West from 1984 to 2015 was twice what would have burned without climate change. It was done by Columbia University and University of Idaho researchers.

They found a strong correlation between forest acres burned and drought, by looking at temperature, rainfall, wind speed, humidity and sunlight data, said one of the researchers, Park Williams, an associate professor at Columbia’s Lamont-Doherty Earth Observatory.

“By just knowing how much drought there was in a given year, we know how we can estimate pretty reliably how much forest fire there was in that area,” Williams said.

From there, the researchers used climate models, temperature records and other tools to explore what they called a hypothetical world, in which global warming didn’t exist, to estimate how bad the drought and wildfires would have been without global warming.

Williams agrees with others who say that a long history of fire suppression has also contributed to the wildfire problem. But a study that would separate impacts of global warming from fire suppression has never been done and would be “monumentally more difficult” than wildfire studies done to date, Williams said.

Wildfires, bark beetles and other factors due in part to climate change have also triggered ecological declines in Southwestern forests, the new report said. Vast numbers of trees have died across Southwest forests and woodlands, with one study showing that tree death in mid-elevation conifer forests doubled from 1955 to 2007, partly because of climate change.

Looking ahead, veteran UA fire ecologist Donald Falk said the populated areas in Arizona most vulnerable to future wildfires are Mogollon Rim communities such as Payson, Pine, Show Low and Greer. All lie in very heavily vegetated steep terrain, in areas where prevailing winds are blowing uphill, whereas fire already tends to move uphill, said Falk, a UA natural resources professor.

“You have situations where fire can move very, very rapidly in rim country, and cover dozens of miles in a few hours,” Falk said. “It can be very, very difficult to get out of the way. “

Southern Arizona’s more open desert country is less vulnerable, with its mountains generally more set back from urban areas, he said.

But Tucson and other cities here are vulnerable to mountain fires that send large amounts of ash and debris down canyons into urban areas. That can trigger huge floods, such as the 2011 Monument Fire that sent huge debris toward Sierra Vista that almost directly hit Fort Huachuca, Falk said.

Extreme heat. In the early 2000s, studies were recording increases in heat-associated deaths and illnesses in heat waves in Arizona and California, due in part to human-caused climate change, the new report said.

An unprecedented 2006 California heat wave, which lasted more than two weeks, is blamed for 600 deaths, 16,000 emergency-room visits and 1,100 hospitalizations, along with economic costs of $5.4 million in 2008 dollars, the new report said.

In Arizona, 1,193 heat-related deaths occurred from 2003 to 2016, state Department of Health Services records show. In addition, at least 2,000 people came to hospital emergency rooms or were formally admitted for treatment for heat-related illness every year but two years from 2008 through 2017, the health records show.

Even higher heat-related death totals for migrants alone are shown in a database kept by the Pima County Medical Examiner’s Office and the group Humane Borders. It lists 3,000 total deaths of migrants whose bodies were found in the desert in this county from 2001 through 2016. Of those, nearly 997 were blamed on heat-related illnesses such as heatstroke and hyperthermia, or were listed as probable or possible victims of such illnesses.

Looking ahead, expect far more days of extreme heat and more heat-related deaths as greenhouse gas emissions continue, scientists say.

In Pima County, expect 52 days in 2050 and 78 days in 2075 of 105-degree-plus temperatures, under the highest possible emission scenario, the UA’s Garfin forecasts based on computer models. That compares to an annual average of 17 such days between 1975 and 2005. With more moderate emissions growth, we’ll get 44 such days by 2050 and 52 by 2075, Garfin predicts.

On a regional scale, under the largest projected increase in carbon dioxide and other greenhouse gas emissions, the entire Southwest will get another 850 additional heat-related deaths by 2050, along with economic losses of $11 billion, the new report said. That would be the biggest increase of any region in the country.

The regional increase would be about half that size under a more moderate increase in greenhouse gas emissions, the report said.

Human health. The new report raises a long list of concerns about other climate change impacts on health.

Climate change and variability can increase risks of communicable and chronic diseases, it said. They include respiratory ailments triggered by bad air quality, mosquito-borne diseases, and infectious diseases such as valley fever.

Besides extreme heat, environmental conditions of greatest concern for human health are ground-level ozone air pollution, dust storms, particulate air pollution, including that from wildfires and dust storms, aeroallergens (airborne substances that trigger allergic reactions), and low water quality and availability, the report said.

Also, alternating episodes of drought and extreme precipitation coupled with increasing temperatures promote the growth and transmission of pathogens.

Respiratory and cardiovascular diseases can be triggered or worsened by a single exposure to ground-level ozone or particulate pollution, the report said. Climate change can trigger any of those problems, it added.

But unlike with wildfires, extreme heat and shrinking water supplies, research documenting climate impacts on other public health conditions here is still not widespread.

Diseases such as valley fever and West Nile virus occur most often in this region within the United States, and valley fever has risen significantly in both Arizona and California in recent years. But studies linking their connection to climate change are sparse.

This scientific conundrum is particularly evident in the case of valley fever’s growth in Arizona, where two-thirds of all the nation’s cases occur. Valley fever, an incurable disease that causes a wide range of painful health effects, has shown meteoric increases in Arizona. Cases jumped from below 1,000 a year in the late ’90s to 5,600 to 7,100 since 2014 (peak years of 10,000 or more cases were 2010 through 2012).

But over the years, there were changes in how the disease is reported and is defined, complicating efforts to pin down causes for the increase, said Heidi Brown, an assistant UA public health professor who worked on the new report.

As valley fever typically works, its fungus lives “out there in the soil, and when precipitation hits at the right time, the pathogen is able to grow,” Brown said. “Once we get into drought periods, it becomes a spore. More dust storms and other dust events aerosolize the spores and when humans or other animals inhale it, we’re more likely to have an infection.

“The short answer is that the data are really difficult to find to prove an association” between climate change and valley fever, Brown said. But “what we understand about the biology leads us to think there probably is an association.”

In California, where valley fever reporting techniques and definitions haven’t changed as much if at all, health authorities have far less problem linking the disease to warmer, drier weather. Valley fever caseloads have doubled or tripled in the past 2½ years, the Center for Valley Fever at University of California-Davis reported this past summer.

Climate change is a factor, as an increasing number of dust storms have spread valley fever’s fungal spores far beyond the Central Valley, where infections had previously been concentrated, said Ian McHardy, the center’s director, in an interview with the California-based website Cal Matters.

“We know there’s a direct correlation between these dust storms and valley fever,” McHardy said, “and we know climate change is increasing the extreme weather patterns here, including the dust storms.”

Contact reporter Tony Davis at or 806-7746. On Twitter@tonydavis987.

Subscribe to stay connected to Tucson. A subscription helps you access more of the local stories that keep you connected to the community.

Get local news delivered to your inbox!

* I understand and agree that registration on or use of this site constitutes agreement to its user agreement and privacy policy.

Related to this story

Get up-to-the-minute news sent straight to your device.


News Alerts

Breaking News