Hot stuff

I have written about wildfires multiple times now, which is concerning, to say the least.

Most recently, I wrote about the summer of 2023, notable for the record fires in Canada and dense smoke that clouded the eastern half of the U.S. for weeks. In that piece, I focused on the need for effective and logical landscape management and pointed out the ways in which climate change might affect wildfires.

There are no simple solutions — one question often leads to another and another and another. So I have been developing a framework to understand and manage complexity as we adapt to our changing climate. Here, I will rely on that developing framework to focus on the complexity around accumulation of heat and its influence on changing wetness and dryness.

Fire and rain

Let’s start with the one thing about climate change that is most certain: Our world is getting warmer. In the case when water is available, more extreme precipitation will occur. This is observed.

But will it get wetter or dryer? That depends on several factors. First, is it raining more? Or is it only raining harder? If it is raining more, is there a large enough increase to balance out the additional evaporation caused by the warmer temperatures? If yes, get ready to get wetter.

So, how do these wetter conditions impact the prevalence of fire?

On one level, the answer is easy: Less fire.

Therefore, one outcome of climate change would be places/time periods with less fire.

Things get more complicated when we think beyond the role of water in suppressing or eliminating fire. One of fire’s three essential ingredients is fuel, and with wildfire, that fuel tends to be trees, brush, grass, and other vegetation. A seemingly positive rainy spring may promote a burst of welcome growth. But this is potentially a burst of fuel if, subsequently, the landscape dries out and goes unmanaged. That burst of wetness in one season can be “remembered” as more fuel a few months later.

Thus we face the counter-intuitive possibility, perhaps even the likelihood, that a wet growing season could set up the ideal conditions for an active fire season, particularly when the growing period is followed by a dry summer and fall.

Dry as a bone

In cases where water is not available from seas, lakes, or swamps, a warming climate will certainly create dryer conditions, even amid rainfall. Guidance from climate models suggests dry conditions will be a recurring theme in any locale that normally experiences both wet and dry conditions over the course of year.

The increased heat will lead to drier soils and drying plants. Vegetation on the landscape will become potential fuel for wildfires. It is this increase in fuel, especially in forests and grasslands, that is expected to enhance the conditions for fire in a warming climate.

Another way a warming climate can affect the availability of fuel is its impact on tree-killing pests. Notably in the western parts of North America, pine beetles have killed many millions of trees. Because of the warmer temperatures, fewer beetles are dying in the winter. In some cases, they have an extra life cycle in the warm season.

Fire is natural

Throughout human history, we have learned to suppress and manage fire, even to the point of believing we can eliminate fire. However, this has proved not to be the case because it is impossible to eliminate all sources of ignition. (There is always lightning.)

It actually is reasonable to think of fire as a type of weather, similar to a storm. Then we can ask, how will a warming climate influence fire?  Since we already experience many types of fires, we should expect that trend to continue. We may see big forest fires, grassland fires, and smoldering peat fires. We may have a large number of small fires and we may have record-breaking large fires. Perhaps most likely, we should expect wildfires in places and during seasons when they have been historically uncommon.

Chatter and controversy often follow the ways in which fires are reported in the press — headlines cry out that large fires are being caused by climate change. Sweeping statements about global wildfire trends are common among experts and non-experts alike. But as with other aspects of climate change, there is no one outcome, no one thing that climate change will do.

Fire walk with me

If we think about what I’ve written here, we would expect a future in which some regions will experience more fires, while others will have fewer fires. Therefore, combining fire measures into a global average obscures the story in important ways. It is certainly meaningless for planning in a region that experiences long wet and dry seasons.

If we focus on regions with drying vegetation, the Sierra Nevada of California, for example, then there are huge changes in the character of fires. The season is longer, and has featured many recent fires of record extent and duration. The same is true in Canada.

With warming temperatures in the eastern part of North America, planners also need to consider increased fire risk. Onset, intensity, and persistence of drought will likely increase. In other words, when there is drought, the drought is likely to be more extreme. I have found the First Street Foundation has developed a credible tool for thinking about fire risk.

Also, as with many of the consequences of climate change, there is a strong dependence on what the conditions are on Earth’s surface, including how we have chosen to manage the landscape. Surface landscape is so instrumental to the science of climate change; it is essential to include it when developing planning scenarios to help us adapt to our changing world.

In my next column, I will discuss the importance of including surface conditions in climate planning.

(Lead image: iStock.)