Here's how much hotter the California desert could get — and how tourism might suffer

Sammy Roth | Palm Springs Desert Sun

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Coachella Valley residents already endure temperatures that can top 120 degrees on the hottest summer days.

But the inland deserts of Southern California are expected to keep getting hotter, with average daily highs increasing as much as 14 degrees this century if greenhouse gas emissions keep rising, according to a report released Monday by state agencies. That kind of temperature increase could spell trouble for tourism in the Coachella Valley.

California's Fourth Climate Change Assessment includes a 67-page section on the state's desert areas, from Palm Springs and Joshua Tree National Park to the farm fields of the Imperial Valley. The report summarizes a vast body of scientific research, painting a devastating picture of how higher temperatures, less reliable water supplies and more damaging wildfires and floods could harm the desert's economy and natural resources, and threaten the health and safety of the region's one million residents.

Here are five takeaways from the deserts section of the climate change report, which was written by scientists from UC Riverside and the U.S. Department of Agriculture.

1. California's inland deserts are getting hotter

The Sonoran and Mojave deserts cover all of Imperial County and most of Riverside and San Bernardino counties. From 1961 through 1990, the average daily high was 81 degrees Fahrenheit across the region as a whole, and 88 degrees in Palm Springs.

Those averages have already begun to increase, and it is "extremely likely" that rising levels of heat-trapping gases in the atmosphere are to blame, the state report says. But the hotter days that desert residents have experienced so far are nothing compared to what's expected in the coming years. If humans keep emitting greater amounts of greenhouse gases each year, average daily highs could reach 90 degrees for the desert as a whole and 97 degrees in Palm Springs during the final decades of this century.

Those are the most likely temperature outcomes predicted by climate models, if heat-trapping emissions continue to rise. But in a worst-case scenario, average daily highs could reach 96 degrees for the desert as a whole and 103 degrees in Palm Springs.

Those are average daily highs, which factor in cooler winter temperatures. The number of high-temperature days each year is also expected to rise dramatically. From 1981 through 2000, Palm Springs had an average of 135 days per year when temperatures exceeded 95 degrees, and 22 days above 110 degrees. From 2070 through 2100, the city could experience 179 days above 95 degrees and 95 days above 110 degrees.

"Already now ... we're seeing temperatures that may have exceeded some of these initial projections," said Neil Berg, a UCLA climate scientist who compiled desert temperature projections for the state report. "It's been a real eye-opening year for me personally, just seeing these changes arriving sooner than I think I anticipated."

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2. Tourists might not spend as much time here

Climate change could spell trouble for the Coachella Valley's most prominent industry.

The state report cites data from the Coachella Valley Economic Partnership showing that tourism generates more than 50,000 jobs and $6.4 billion annually for the region's economy. Much of that economic activity is driven by part-time residents known as "snowbirds" and other tourists who visit the Coachella Valley in the winter, when mild temperatures make the region an attractive alternative to cooler, snowier locations.

But the region's ideal snowbird season will likely get shorter as temperatures rise. Climate models predict the number of days with high temperatures in the 70-85 degree range will shrink from a period of 5.5 months to about 4.5 months by 2050, then to as little as 3.5 months by 2100. In that worst-case scenario, a tourism season that currently lasts from November through May could instead run from December through March.

"By the end of the century, this represents a reduction of 25-33% in days with favorable temperatures for outdoor activities that are popular tourist attractions in the Coachella

Valley, such as golf, tennis, and the Palm Springs Tramway," the state report says.

The report also points to major outdoor events such as the Coachella Valley Music and Arts Festival, Stagecoach and the BNP Paribas Open tennis tournament. Organizers of those springtime events "will have to either shift their dates or provide more cooling infrastructure to accommodate their guests" due to extreme heat, the report says.

3. Fires and floods could happen more often

California's inland desert region received just 5 inches of rain per year on average during the middle of the 20th century, making it the driest part of the state.

The overall amount of rainfall in the desert may not change much over the course of this century, climate models predict. But climate change is expected to cause even more dramatic swings between dry and wet years than the desert experiences now.

"This variability is projected to increase over the coming decades, with extreme drought

and extreme wet events both becoming more common. In turn, increasing frequencies of these extreme events will increase the risk of flash flooding and wildfire, given the close relationship between precipitation variability and growth of invasive grasses that serve as the major fuel for wildfire in the region," the state report says.

The report points to the July 2015 collapse of a bridge along Interstate 10, an hour east of Palm Springs, as the kind of event that could happen more often as climate change brings more frequent flash floods. The loss of the Tex Wash bridge temporarily severed the primary route between Arizona and Southern California, and injured one driver.

"Bridges like this are being rebuilt with deeper foundations," the report says. "Wildfires can also directly affect the transportation infrastructure, literally melting pavement and buckling concrete."

4. The Salton Sea crisis could get even worse

The Salton Sea is California's largest lake by surface area, but it's shrinking. The desert lake doesn't have a natural source of inflow, and the agricultural runoff that's sustained it for years has been dropping as Imperial Valley farmers irrigate crops more efficiently and sell some of their water to cities in San Diego County and the Coachella Valley.

The shrinking lake is an environmental and public health crisis: Less water means less habitat for migratory birds, and more exposed lakebed means more toxic dust being whipped into the air by the desert's fierce winds. The windblown dust is worsening the air quality in a region that already has high rates of childhood asthma and heart disease.

Experts have estimated that without significant steps to address Salton Sea's problems, the economic damage over 30 years could range from $29 billion to $70 billion, including higher health care costs for illnesses and lower property values. And climate change, the state report says, "poses an additional threat not included in these assessments."

"Climate change will exacerbate stresses to the limited water supply feeding the Sea and may accelerate the pace of decline," the report says.

Rising temperatures and less reliable water supplies are also likely to harm agriculture, which is the economic lifeblood of the Imperial and Palo Verde valleys, and a major economic player in the Coachella Valley. California's inland deserts are already "at the high temperature limit for agriculture," and climate change "will bring additional heat stress to field crops, livestock, and the health of farm workers," the report says.

5. Joshua tree habitat will probably shrink

California's inland deserts are considered a biodiversity hotspot, known for iconic species such as desert tortoises, Joshua trees and Mojave fringe-toed lizards. The state report says the region is home to 37 percent of California's plant species despite accounting for just 28 percent of its physical area. Those plants and animals populate the landscapes of some of the country's most treasured public lands, including Joshua Tree National Park, Death Valley National Park and Mojave National Preserve.

But the desert's high level of biodiversity "is a product of localized refuges from climatic extremes that will likely contract as the climate warms," the state report says. In other words, the types of habitat that make life possible for many of the desert's unique species will become fewer and farther between as global temperatures steadily rise.

"A warming and likely drier climate, with more intense and prolonged droughts, would clearly stress populations anywhere," the report says. "For those species already near their presumed physiological limits living in deserts, there is reason for concern."

Some iconic species could be at risk, including desert tortoises and Joshua trees. Researchers have predicted that Joshua trees, formally known as Yucca brevifolia, could vanish from 90 percent of their current range in the national park named for them.

Neil Berg, the UCLA climate scientist, said the state report offers some reasons for hope. He pointed out that many of the impacts of climate change would be lessened under a scenario where human beings reduce their planet-warming emissions.

"People ask me all the time, 'What is the real benefit of transitioning off of fossil fuels?' Well, half of the change in the hottest day of the year, which has pretty critical impacts on public health, water resources, electricity demand and so forth," Berg said.

Sammy Roth writes about energy and the environment for The Desert Sun. He can be reached at sammy.roth@desertsun.com, (760) 778-4622 and @Sammy_Roth.