Climate Change in the Southwest

“Fires, flooding and climate change are completely connected.” ~ Peter Fulé

Melting glaciers, ocean acidification, rising sea levels. We often hear about catastrophic examples of climate change in far flung places. But what are the local implications of a changing climate for the Southwest? Two very important ones are more intense wildfires and flash flooding.

HISTORY OF THE LANDSCAPE AND FIRE

Both floods and fires are natural disturbances, according to Tayloe Dubay, knowledge specialist at Northern Arizona University's Ecological Restoration Institute. Dubay said that these forces have shaped the Southwest for millenia.

Dubay said historically, low-burning, low-severity lightning strike fires thinned the vast ponderosa forests of Northern Arizona, maintaining the health and diversity of the ecosystem. By removing some trees and dead debris from the landscape, fire ensured other trees would have adequate resources to mature. Bigger, mature trees have thick bark plates which makes them more resistant to fire.

However, in the early 1900’s the United States Forest Service declared what’s known as “the war on fire”, according to Paul Oltrogge, wildland fire management officer for the City of Flagstaff. After decades of overgrazing and logging had already altered the forest structure and fire frequency, what would become a legacy of fire suppression in the West began. And now, after over a century of fuel build up, forests across the Southwest are overgrown and ready to burn.

The Rafael Fire (2021) burn scar near Sedona, AZ.

FLOODs, FIRES AND CLIMATE CHANGE

“Fires, flooding and climate change are completely connected,” said Peter Fulé, fire ecologist at NAU’s School of Forestry. Both living and dead plants protect the surface of the ground from the impact of rain drops, and extreme fires can completely strip the landscape of vegetation. The powerful monsoon rains that follow, intensified by climate change, pound the earth, leading to increased runoff and flooding.

Fulé said that another important connection between floods and fires is the chemical reactions between the extreme heat and waxes and resins in vegetation. Some of these compounds are completely consumed during a burn and some go up in smoke particles, but some melt and re-harden in the upper layers of the soil. This hardened hydrophobic, or water resistant, layer repels rain, increasing runoff.

An eroded wash near the Museum Fire (2018) burn scar outside Flagstaff, AZ.

CLIMATE CHANGE AND TYING IT ALL TOGETHER

Notwithstanding the effects of climate change, human management and certain land uses would still have increased the presence of megafires and floods in the Southwest, according to climate research PhD student Christopher Hancock. However, the combination of land management choices and climate change has aggravated both flooding and fires in never-before-seen ways.

Warmer temperatures induced by climate change have dried out the landscape, leading to dryer vegetation and less moisture in the soil, according to Jenny Niemann, the climate program manager at the City of Flagstaff. Dryer vegetation burns more easily. Additionally, rising temperatures make trees more susceptible to pests and disease, which stresses and weakens them.

Not only that, but Niemann said climate change is also leading to prolonged drought. The Southwest is currently in a long term drought, and we will continue to see extended dry periods and more extreme heat waves. Niemann paints a picture of what the Southwest will experience as a result of climate change.

“Generally,” said Niemann, “the changes Flagstaff is going to see are similar to the Southwest in that we’re going to see more frequent and more severe wildfires.” Since fires and floods are inextricably linked in our regions, communities also need to be prepared for increasing damage from flash floods.

Beyond increasing fire and flooding intensity and frequency, Hancock said greater aridity across the Southwest will contribute to longer fire seasons and earlier snow melt. Precipitation patterns are shifting as well. Hancock said we will see increased rain during the winter rather than the expected snowfall.

Niemann said that landscapes like the ponderosa pine forests in Northern Arizona have adapted to absorb moisture from snow which melts very slowly, rather than intense and short-lived monsoon rainstorms. Moreover, Hancock said that these intense rains can overwhelm the capacity of the soil to absorb that moisture. This all contributes to drying out the landscape and vegetation, exacerbating droughts, fires and floods.

WHERE DO WE GO FROM HERE?

So what now? Hancock said that making decisions to combat climate change are not all about reducing CO2 emissions, but that communities also need to consider issues like what projects they choose to fund and where they choose to build.

“It’s not just one solution,” Hancock said about climate change. “It has to be an integrated, societal change.”

• 

• 

• 

(2) Flooding aftermath near 4th Street, Flagstaff, AZ. (2) Museum Fire burn scar and erosion (3) Old burn scar near the Rafael fire site, near Sedona, AZ.