Wildfire in a Warming World

Wildfire has been a hot topic in the national news recently, with California ablaze due to a combination of dangerous fire weather, ongoing drought, and scores of drought-and beetle-killed trees. The scale of forest mortality is striking. I’ve seen it firsthand during trips to visit family in the southern Sierras, where there are an estimated 66 million dead trees. The normally evergreen hillsides are tinged a rusty red (see photo above) and long-standing backyard trees are being felled to reduce fire risk near homes and other structures. One of the most heart wrenching for us was the loss of the two ‘sentinels’ in my father’s backyard.

The forest is a tinderbox and it doesn’t take a trained eye to see the fire risk. With this build-up of dry fuel, it is perhaps unsurprising that California has had several severe fire seasons in recent years. But it isn’t the only place experiencing an increase in fire activity—wildfire has been increasing across the western U.S. in recent decades. Since the 1970’s, the number of fires, area burned, and frequency of large fires have all increased.

What’s causing the uptick? Well, a long history of fire suppression and recent forest mortality events certainly contributed, but research suggests climate is also playing a major role. Hotter and drier weather combined with earlier snowmelt—all of which are symptoms of climate change—have increased the length of the fire season and the amount of acreage burned. Trees require more water as temperatures rise, which quickly leads to water stress during dry periods. Severe water stress makes them vulnerable to drought-induced mortality and less able to fend off insect attacks. For this reason, warmer temperatures alone can be a cause for concern when it comes to forest health, especially in drier ecosystems like those found out west

The 2014 National Climate Assessment noted that climate change-related fire is increasing the vulnerability of U.S. forests to ecosystem change and tree mortality. This is a big concern because important ecosystem services may be disrupted (e.g. forests purify our air and water) and fire moves forests from being carbon sinks to carbon sources, which increases emissions and accelerates warming. As owners and managers of forestland across North America, the members of Manomet’s Climate Smart Land Network (CSLN) are also grappling with this challenge. Forest managers want to understand how local fire regimes may be changing, so they can take steps to reduce fire risk, adjust their planning, and make sure there are sufficient fire management and response systems in place. To meet this need, the CSLN team recently delved into the latest research on wildfire and climate change. If you’re interested in learning more, check out the September bulletin from the CSLN.