Endure, Evade, or Evacuate

Climate Change in Tucson and the Surrounding Desert Region

by Katie Predick, Conservation Research Scientist

February in Tucson 

Snow dabs mountaintops and our breath puffs visible on morning walks. Last week I considered purchasing an ice scraper to save my debit card some wear and tear. Even so, freezing temperatures are less common than decades ago. Regardless, we all know the heat is coming. And like all desert animals we will endure, evade, or evacuate.  

A graph titled "Nights Below 32 degrees" shows how the number of freezing nights in Tucson has decreased steadily from 1970 to 2022.
Via climatecentral.org

Desert Animals 

As the climate warms, enduring and evading will become more challenging for desert dwellers. While some species will be well equipped to weather these changes, many others are at risk, such as desert tortoises that breed and grow slowly and depend on desert plants. Tiger whiptail and zebra-tailed lizards are vulnerable to warming temperatures because they are active during the heat of the day and breed during the summer.

Conversely, some species will likely endure increased temperatures. Tree lizards avoid intense heat and depend on woody species likely to do well in a warming climate. Desert mammals already use a variety of strategies to avoid the heat, such as burrows and limiting activity to cooler parts of the day. Many species will face indirect risks, such as competition from new species or changes to preferred food sources, plant or animal. 

Desert Plants 

The vegetation currently emblematic of our local desert is likely to change. The shallow-rooting thorny shrubs and trees of the southern Sonoran Desert will move north, creating landscapes resembling Mexican Sinaloan thornscrub ecosystems (see pictures of coastal thornscrub below). Cacti are well adapted to heat stress as adults, but not as seedlings. Young prickly pear, cholla, and especially the iconic saguaro may have difficulty surviving heat and drought to reach adulthood.

Warmer, drier winters with more sporadic rain will favor invasive grasses, like buffelgrass. As drought and invasive grasses increase, so will fire risk. Buffelgrass can often take over after fire, which it tolerates while native species do not, so there is risk of a positive feedback loop of invasive grasses and fire. 

Desert Heat 

The southwestern U.S. is warming faster than any other region in the country (excepting Alaska). Tucson is ~4.6F hotter than in 1970, while the rest of the contiguous states average 2.6F hotter. While Tucson is warming year round, the greatest increase in temperatures has occurred in the spring and fall; winter is warming the slowest. However, winter warming will have a large impact as freezing temperatures restricts the range of some species in the southern Sonoran Desert. Changes to rainfall may be even more important than increased heat. 

A bar graph shows how temperature change from 1970 to present day varies between Tucson (+.4.6), Arizona (+3.3), and the United States (+2.6).
Via climatecentral.org
A line graph titled Seasonal Warming shows how the four seasons have experienced significant degrees of temperature warming from 1970 to 2021.
Via climatecentral.org

Desert Rain 

Water defines life in the desert. Hillsides and gardens turn green after rainfalls and senesce to yellows and browns in periods between. Concerns about drought are paramount across the western U.S., particularly in relation to fires and the Colorado River. The amount of rain we receive in Tucson will decline with climate warming, but changes to the timing of rainfall may be more impactful. 

Winter rains are coming later in the season and so water isn’t available until the weather is colder. Ironically, this favors winter plants that prefer cold temperatures to sprout and grow. Winter rains will also end earlier, limiting winter vegetation growth and lengthening the fire season.

Paradoxically, even as drought risk increases so does flood risk. While we’ll receive less rain overall, it will be concentrated into fewer storms. We will experience more spectacular, large monsoon storms with longer periods of drought in between. Plants and animals will have to contend with longer periods without water during the typically wetter times of year, stressing growth and reproduction. 

Two palo verde trees dripping with moisture frame several saguaros in a Sonoran Desert post-monsoon rain scene.
King Canyon in Tucson Mountain Park after summer morning rainfall.
A creosote bush in bloom with yellow flowers.
The creosote bush (or greasewood) is associated with the smell of rain.

The unique scent associated with rain in the desert may become stronger. Plants create the smell by emitting a wide variety of compounds in response to rain, which have mental and physical health benefits. Heat stressed plants emit more of these compounds and species likely to spread from the south are high producers.  

What Can You Do?

Climate change is a complex, global issue that requires collective action on a large scale. However, our personal and local actions matter, too.

The City of Tucson has recently released a draft of the Climate Action and Adaptation Plan for the City; public comments are being accepted until February 21, 2023. Please make your voice heard!

Project Drawdown has evaluated and compiled a list of 72 ways to reduce climate change. While many of these require action from industry or government, there are impactful actions everyone can take: eating more plant-based food and reducing food waste are ranked in the Top Five.

Featured Image by Frankie Lopez.

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