5 ways wildfires can affect cities - even thousands of miles away

Thousands of people in Quebec, Canada evacuated their homes this month due to raging wildfires. More than 400 miles away, New York City experienced its worst air quality in history, and briefly had the worst air quality of any city in the world. And New York wasn’t alone: As of June 7, 2023, more than 75 million people in the United States were experiencing unhealthy and even hazardous air quality due to fires burning hundreds of miles away.

The catastrophic effects of the wildfires in Quebec make it clear that a forest’s impact — or the impact of its destruction — expands far beyond the forest itself. And while the effect on air quality is the Quebec wildfire’s most visible impact, wildfires affect cities near and far in multiple ways — from harming economies to heightening flood risks.

It’s also a problem that’s worsening. While wildfire is an important ecological process in many forest ecosystems and prescribed burns can be an effective forest management tactic, declining forest health and climate change are causing wildfires across North America and the world to become catastrophic. According to data on WRI’s Global Forest Watch platform, forest fires are burning nearly twice as much forest cover today as they did 20 years ago.

Here are five examples of how wildfires affect cities hundreds or even thousands of miles away:

As the wildfires in Quebec illustrate, wildfires can have immense and widespread impacts on air quality for city residents. Specifically, wind can push smoke from wildfires across hundreds of miles. The fine particles in smoke pose the biggest threat to human health, as they can cause burning eyes, respiratory illnesses like bronchitis, and aggravated symptoms for people with chronic heart or lung conditions. For example, at one point, the air quality index in New York City was 484; the U.S. Environmental Protection Agency categorizes any air quality index over 150 as unhealthy for the general public.

In addition to creating poor air quality, wildfires produce greenhouse gases that fuel climate change. Because trees store carbon, they release carbon into the air as they burn. The wildfires in Canada, for example, have led to record-breaking carbon emissions.

After the wildfire concludes, some of the carbon will be recaptured as the forest recovers, but the loss of trees reduces a forest’s ability to capture and store carbon for many years. Given that U.S. forests sequester roughly 12% of the nation’s carbon emissions per year, large forest losses can worsen the climate crisis.

Forested watersheds are vitally important to many cities’ water quality and quantity. Thirty-three of the world’s 105 largest cities rely on forested watersheds to supply their water, as do many smaller cities. Forests and trees increase infiltration and reduce rates of erosion, both of which prevent sedimentation and other pollutants from reaching rivers and lakes crucial for water supplies.

Additionally, forested watersheds can help ensure consistent water supplies year-round and recharge groundwater. Trees in a forest store and release water vapor, which can regulate weather and rainfall. The canopy and roots of trees can also help slow the flow of runoff, releasing water into downstream systems more gradually.

Catastrophic wildfires cause losses in the forest canopy and affect the soil underneath it. With fewer trees to intercept water runoff from storms and unstable soil that is more prone to erosion, more sediment, ash and pollutants will flow into lakes, rivers and reservoirs. Deforested watersheds thus experience poorer water quality and less ability to hold water. Both of these impacts result in less clean drinking water for the cities and other areas that rely on forested watersheds.

Cities are especially susceptible to flooding. Urban areas have high amounts of impermeable surfaces, such as sidewalks and roads, which results in more runoff when it rains. Healthy forests near cities increase infiltration into soil, store excess runoff and slow water down. In other words, they can act like sponges and barriers that protect downstream cities from floods.

When heavy rainfall happens in an upstream forest after a wildfire, there is no tree canopy to slow down the water and the soil is less able to store runoff. As a result, flash floods can happen with even relatively small amounts of rainfall. For example, in Mora County, New Mexico, flooding after the Hermits Peak-Calf Canyon fire in 2022 damaged homes, while rural farmers lost cattle and game meat as a result of power outages.

This is not a short-term risk: It can take years for vegetation to grow back after a wildfire, leaving cities and other communities at risk for just as long.

Each of these impacts can result in negative economic effects:

Wildfires can also reduce economic activity. In the summer of 2018, 11% of tourists cancelled their trips to California due to wildfire concerns, even to areas unaffected by wildfires. This led to $20 million dollars in lost revenue for the state’s tourist economy in one month alone. In California’s Napa and Sonoma Counties, reduced tourism also led to higher rates of unemployment, largely in the leisure and hospitality sectors.

While city residents may be located hundreds of miles away from forest fires, they are not powerless to do something about them. By making forests more resilient to wildfires, cities can protect their communities. Here are a few ways they can act:

Despite the smoke clouding many cities, the path forward is clear to see. Cities have much to gain from wildfire resilience, and they have a unique vantage point to get money flowing toward mitigation and resilience projects. Now is the time to see if the recent air quality scare will serve as the wake-up call needed to move cities to action.