Wildfire Season: Now A Mere 12 Months of the Year

It’s pretty much always wildfire season now, but with Memorial Day weekend here, it’s worth reviewing how fire and climate change works together.

While forest management and human development have increased wildfire incidence and risk, climate change has exacerbated the trend of large fires and contributed to the lengthening of the fire season, in some cases making wildfires a year-round phenomenon. In the Western US, climate change is a major driver behind the near doubling in burned area that we’ve experienced over the past 35 years, and has contributed to an increase in the frequency and severity of fires, while lengthening the fire season in some regions.

Fires also simultaneously aggravate the impact of climate change by releasing huge quantities of carbon dioxide and other global warming gases into our atmosphere.

As the first act of this new fire season begins to unfold, we have a renewed opportunity and obligation to address the connections between wildfires, climate change, and human activity, and take steps to interrupt this vicious cycle.

Drought is a natural occurrence. However, now we have a greater risk of hotter droughts. Rising temperatures dry out soils and trees. While drought means that less water is entering the ecosystem, rising temperatures mean that water is leaving more quickly. As temperatures rise, plants lose more water per unit of carbon dioxide, exacerbating the already dry and dangerous conditions produced by drought.

With less water coming into the ecosystem, plants become water stressed, which can kill huge numbers of plants if drought conditions persist. In extreme cases, drought itself can kill trees. Plants lose water when they perform photosynthesis, the process where plants use sunlight and carbon dioxide to make food, because they open their pores (aka stomata) to take in carbon dioxide, and water evaporates out in the process.

(This is such a big deal for plants that some have evolved special processes so they can avoid this water loss. In the desert, many plants only do gas exchange at night, when temperatures are lower and water-loss risk is the lowest.) #CAMLife #DinnerPartyFactoid

So in periods of extreme water stress like drought, they close those same pores to conserve what water they have. However, since plants aren’t able to photosynthesize with their stomata closed, they then use up their carbon reserves and literally starve, known as carbon starvation.

Hydraulic failure is another way drought can lead to plant death: where air bubbles in the xylem (water transporting plant tissue) block water transport and the plant dies. When droughts are longer and more severe, the risk of hydraulic failure increases.

Alternatively, trees can also die from complications associated with drought, like an insect infestation that a healthy tree could usually defend against. Climate change has magnified the negative impacts of insects, as in the case of California’s bark beetle. Cold temperatures have historically regulated the populations of these insects, but as climate change continues to shrink the temperature range that any one given ecosystem experiences, these cold temperatures just aren’t happening anymore. These insects also grow and reproduce more quickly in warmer temperatures, which may further enhance their spread.  While these outbreaks and subsequent tree deaths are changing the overall composition and structure of the ecosystem, they also can lead to a build-up of dry forest kindling. As a result, we can expect that forests in the West, Southeast and Alaska will continue to be full of dried out, ready-to-burn material.

There’s more if you want to deepen the depression this should make you feel.