In early March 2017 rain spattered across the Sonoran Desert. At Tumamoc Hill near Tucson, Arizona, seedlings and flowers sprung up atop the hillside research center.
A week after the rains temperatures reached mid-90 degrees Fahrenheit for several days. The seedlings and flowers atop Tumamoc Hill sweltered and died in the heat. During that time, the region experienced little rain.
“It looked like it was going to be a really good spring germination and flowering period,” said Benjamin Wilder, interim director of Tumamoc Hill Research Center. “But after those two weeks [of heat], it just toasted everything.”
The American Southwest is naturally a hot region with sporadic weather, but climate change is making it even hotter with more extreme weather conditions.
“In the landscapes in Arizona, it’s subtle because we live in an arid place,” said Daniel Ferguson, director of CLIMAS. Climate Assessment for the Southwest (CLIMAS) is a NOAA RISA team at the University of Arizona’s Institute of the Environment. It is dedicated to climate change research and the sustainability of life in the southwestern United States.
The main impacts of climate change in the desert are hotter temperatures and less rain. This leads to more extreme drought, less hard freezes and higher probabilities for wildfires and invasive species. It also impacts many human activities in the southwest.
“What is expected and forecasted for this region is hotter and drier and less rain,” Wilder said.
Since the change is occurring so quickly, plants that have adapted to the desert heat find it challenging to adapt to warmer winters and drier summers in the quick period of time in which climate change is occurring.
Wilder explains how this region of the Sonoran Desert is dominated by large shrubs, trees, creosote flats, cactuses and especially the “dominate saguaro cactus.” In the Sonoran Desert, the flora is 50 percent tropically derived species and the other half is more temperate. The region serves a mixing point of the Chihuahua Desert, Great Basin and Mojave Desert, combined with tropical plants travelling northward from Mexico.
Climate change not only affects the native plants, which are naturally equipped to handle heat and little precipitation, but also the invasive species that are coming into the region. Many invasive species are travelling northward from Mexico, because the deep freezes that once limited their ecological range are becoming less and less frequent.
“If we get a lot of moisture in the fall,” said Ben McMahan, outreach coordinator and researcher at CLIMAS, “some of the non-natives are able to take advantage of some of the moisture and elevated temperature, either late in the year or early spring before some of the native plants get going.”
One problematic invasive is buffel grass. With invasive grasses like buffel grass filling in the empty spots in the desert, it makes it easy for a simple spark to start a wildfire than can burn 20,000 acres in two days, as did the Sawmill Fire in the Santa Rita mountains in late April 2017.
“Invasive grasses come in,” Ferguson said. “We end up with an increase in chance for fire, and natives aren’t adapted to fire.”
The effects of fires and climate change are not only for ecological system changes – they impact humans as well. One unusual impact is in Tucson’s electrical grid.
“You don’t think of wildfire as something that can knock out the electrical grid, but in the right low-probability scenario those things can happen,” McMahan said. “The smoke affects the transmission lines for the electrical grid.”
Tucson Electric Power also provides trees from local nurseries to their consumers for a reduced price. With climate change in mind, the motto of this incentive is: “Plant a Tree. Create Shade. Conserve Energy.” Planting a tree provides shade, which reduces energy costs, but also promotes clean air and xeriscaping with local plants.
Another side effect of less precipitation and hotter conditions is drier and dustier air. For many people, this causes a problem with allergies and air-borne diseases.
A recent study on the connection between soil moisture and the fungus coccidiodomycosis (valley fever) states there is evidence that drier periods of time allow spores to travel more freely. This means that as the region experiences more drought it will be easier for humans and animals, particularly dogs, to contract valley fever. The study was published by GeoHealth in March 2017.
“High impact, low probability events,” McMahan said. “These are things that are hard to predict and don’t happen very often, but when they do they have the potential to cause a lot of problems.”
One event that has high impact but high probability: the availability of water.
“There is a great snow in the upper basins,” McMahan said, “but it’s so warm up there that it’s actually melting off a lot sooner. So the water is still in the system, but it’s coming through the system much sooner so it has more chance to evaporate.”
Water is essential to the feasibility of life in the desert and affects both humans and ecosystems, like on Tumamoc Hill.
“You could question,” McMahan continued, “if this state’s population keeps growing, is there going to be enough water, no matter how much we conserve?”
The Assessment of Climate Change in the Southwest U.S. reports how water demands increase with higher temperatures, quicker snowmelts, and increased evapotranspiration by plants and water temperatures. The assessment predicts that the Colorado River will decrease in stream flow in the next century, and water supply and demand strategies must adapt to changing climate and populations. Possible solutions? Desalination plants in San Diego, financial incentives in Las Vegas and more dams in Colorado to control stream flow.
“We are definitely moving towards a point past normal,” Ferguson said. “What happens when you’re outside the envelope of what species are used to? It seems inevitable. It’s not questionable that we’ll probably reach that point.”
But even climate change cannot stop many of the native cactuses from blooming. In late April, the typically brown and green desert landscape is punctured by reds, yellows and oranges from the beautiful flowers that bloom on the fruits of cactuses.
“It’s a paradox of scarcity but abundance,” Wilder mused.
Links to the research mentioned in this story:
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