What to Know About Climate Change in Our Own Backyard
1. It All Begins with Heat
You think summer is toasty now, consider that by the end of the century annual average temperatures in Tucson (and all of the Southwest) are projected to be hotter by upwards of 9° F, depending on measures taken immediately to decrease carbon emissions. Put another way, Tucson’s climate, summer and winter, is on track to be more like Death Valley is today. Make note that Death Valley recorded a world record 129.9° F on August 16, 2020.
The higher temperatures are not just on tap for the daytime, but evenings, too, depriving us of one of the benefits of living in Tucson and not warmer Phoenix: our mild summer nights.
Also projected (climate research rates it as a "high certainty"), an increase in "very hot days" and hotter heat waves. We've already experienced what's in store in terms of heat waves. June 2017 was Tucson's hottest June in 120 years of recorded temperature history, searing us with a three-day heat wave with temperatures in the 115°–116° range and two weeks at the end of the month when temperatures were 105° degrees or more every day.
2017 has been eclipsed by 2020, when Tucson experienced its hottest summer on record. We had 74 days when the daytime temperature was at least 100° and 50 days when temperatures reached 105° and above. Our average low temperatures were also the hottest ever, with 33 days when nighttime lows never fell below 80°.
No Raindrops Falling on Our Heads
While higher temperatures are a given, we really never know just how much rain our summer monsoon will deliver. Monsoon season provides our desert with more than half of our annual rainfall. Predicting that rainfall, says Gregg Garfin, is always "a 50-50 proposition." What is known: Tucson’s precipitation, winter and summer, has been lower during the last three decades than the long-term average for the first half of the 20th century.
The 2020 monsoon turned out to be a nonstarter. Climatologists here call what we had a "nonsoon" event. Rainfall was scant, 1.67 inches compared to the average 3.17 inches. Drought is our present and future.
2. Heat, Water and the Snow Pack
Temperature as it heats up has an effect on most everything in our lives. Most perilous is its impact on precipitation and most notably on snow. The increase in temperature is already affecting snow hydrology and snow melt — there is less snow-covered area in the western U.S. now than in the past, less water in the winter snow pack, and snow is melting sooner, but not always as water that seeps back in and replenishes the earth. Higher temperatures lead to conditions where snow now is more frequently reduced to mere vapor (a process called "sublimation"). Increased sublimation means lower soil moisture and that results in less runoff, which is critical for replenishing the soil, streams, and reservoirs.
3. Climate Change and Ecosystems
Higher temperatures, less snow, earlier snow melt, less soil moisture, erratic rain storms. What do they add up to? Conditions, said Garfin, that kill trees and put more trees at stress. “We’ve seen pretty big conifer mortality increases from Mexico to Canada over the past few decades.”
Those conditions also portend what the West, and California in particular, is already experiencing: longer fire seasons. Referring to findings in the Fourth National Climate Assessment, Garfin noted that the total acres burned by fire today is roughly double what would have burned without the already occurring impacts of climate change.
As we've seen in California, particularly in 2020, fires today are also burning hotter and moving faster, ignited by dry and dense underbrush and invasive grasses. Adding insult to injury, rain that falls after large fires often careens down mountain slopes triggering massive debris flows and post-fire floods, both of which can threaten the water quality in reservoirs.
One such debris flow destroyed the topmost portions of Sabino Canyon in 2006 following an unusually heavy July rainfall. A follow-up study by the Arizona Geological Survey concluded that these flows could increase due to fires in the adjoining Santa Catalina Mountains. The 2020 Bighorn Fire, the largest fire in the Catalinas in recorded history, had the potential for re-creating the damage caused to Sabino Canyon. What prevented disaster: no rain.
Wildfire Projects, with and Without the Impacts of Climate Change
Figure 25.4: The cumulative forest area burned by wildfires has greatly increased between 1984 and 2015, with analyses estimating that the area burned by wildfire across the western United States over that period was twice what would have burned had climate change not occurred. Source: adapted from Abatzoglou and Williams 2016. Chart from the 4th National Climate Assessment.
4. How Dry We Could Be
Drought is not an anomaly in the Southwest. We have our natural-occurring share of short-term droughts. But higher temperatures and longer, hotter heat waves; precipitation variability; and less runoff from snow melt increase the risk of long-term, extended dry periods. Arizona had emerged from a multi-year drought, thanks to a rainy May 2019, until the summer of 2020. Now we're dry again and back in drought. Also impacting the likelihood that drought will continue to threaten our region, as noted by Garfin: indications that the jet stream may migrate to the north. Not good news for our region because the change could affect winter and spring rain patterns.
Darker the red, deeper the drought. The deep red conditions shown here and representing the latter part of 2020 primarily occur on Native lands, the Tohono O’odham in Pima and Pinal counties and the Navajo north along the Utah border.
5. Water, Heat, and Public Health
Demand for more water and increased use of cooling systems is expected as temperatures rise and we begin to experience longer summers. It is only logical to assume that residents will turn on their cooling systems earlier and keep them on longer, notably into the night as we sleep through higher evening temperatures.
But there are also concerns about health risks related to heat and periods of drought, both of which could provide pests a longer breeding season, with the possibility that new mosquito-borne diseases may migrate to our region, among them Dengue Fever.
(To learn more about the projections for Dengue Fever and other diseases that may be on our way, check out the August 11, 2020 Climate Tucson presentation by University of Arizona epidemiologist Kacey C. Ernst.)
6. Extreme Rain Events
Oh, the irony. Projections for a decrease in precipitation overall due to climate change also take into account the nature of our primary rain generator, the monsoon season. Monsoon rain falls from towering cumulonimbus thunderclouds that can sprawl for miles and soar upwards of 69,000 feet in altitude. Higher temperatures increase the capacity of these giant faucets to hold moisture — and the irony here is that while we may see less rain overall, we could experience extreme rain events, in the summer especially, which would increase the risk of even more flooding than our region experiences now from flash floods. Garfin noted that research out of the University of Arizona confirms that while the risk of isolated extreme rain events is increasing, the number of dry days is also increasing — so more of our summer precipitation is coming in fewer and more intense events.
7. What About Agriculture?
Tucson imports 97% of its food, a good portion of it from Mexico, so what happens outside our region is crucial to our quality of life. Obviously, agriculture is affected by high heat and drought, which in turn affect what we can grow where. It’s no small matter to swap out crops or dig deeper wells or retool operations to make those changes (the cost passed on to the consumer).
Figure 25.9: The U.S. Department of Agriculture plant hardiness zones indicate the cold temperature requirements of crops. Increases in temperature under the higher scenario (RCP8.5), would shift these zones northward and upslope, from the period 1976—2005 (left, modeled historical) compared to projections for 2070—2099 (right, average of 32 general circulation models). Sources: NOAA NCEI and CICS-N. Chart from the 4th National Climate Assessment.
8. Then There's Water Infrastructure
What we have now needs immediate attention, even before we talk about updating infrastructure to adapt to a changing climate.
According to the American Society of Civil Engineers’ (ASCE) Report Card on the state of the nation’s infrastructure, Arizona has 214 structurally deficient bridges and 108 high-hazard dams, and 15% of our roadways get a “poor” rating. Those gaping potholes and other driving distractions cost motorists an average $481 a year each in repairs
As for water infrastructure, Arizona’s approximately 800 community water systems need $7.4 billion over the next 20 years for their drinking water systems, ASCE reports, for funds to replace or rehabilitate deteriorating water lines ($5 billion); construct, expand, and rehabilitate treatment infrastructure ($1.4 billion); construct or rehabilitate water storage reservoirs ($684 million); and construct or rehabilitate wells or surface water intake structures ($334 million).
State wastewater systems will require $6.77 billion for infrastructure needs over the next 20 years, according to ASCE.
Another obstacle: While we have standards for building in earthquake zones, for example, water management and civil engineering sectors have yet to recognize climate change as a risk in their professional standards and guidelines. “Climate change has not been systemically included,” said Garfin.
9. Could be Worse
