Wildfires and Droughts
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In our previous installment, we covered hurricanes, storms, and monsoons – how they form, how they function, and how climate change can impact them in the coming decades. For Part 2, we’ll change gears entirely and move on to the polar opposite of storms and monsoons – droughts and wildfires. As with storms, droughts caused by climate change are projected to occur worldwide, but for this article, we’ll focus on the effects in the United States – specifically, droughts in the Southwest and wildfires in the Pacific Northwest.
As always, it is important to note that many ecosystems are dependent on seasonal dry months and wildfires as part of natural processes. Fire-dependent ecosystems, like forests, shrublands, and grasslands, evolved with semi-frequent wildfires, and rely on them for various reasons, like soil rejuvenation and seed germination. Sequoias, for example, have fire-resistant bark, and depend on regular, low-to-moderate intensity fires to break open their seed cones and clear away competing undergrowth. Such fires basically act as a “refresh” button for dependent ecosystems, cycling soil nutrients, torching undergrowth and potential invasive species, and allowing seedlings to grow in the aftermath. In fact, traditional fire suppression tactics tend to cause long-term harm to ecosystems, and can even be counterproductive – extinguishing the smaller, weaker fires causes a buildup of undergrowth, dead plant matter, and other fuels, resulting in stronger, more destructive fires that are much more difficult to extinguish.
How does climate change affect fire and drought cycles? Increased temperatures cause greater water evaporation from the soil. Warmer winters mean that more precipitation falls as rain instead of snow, and snowpacks in the mountains do not build as high. Higher temperatures also melt these snowpacks earlier in the year. Many areas depend on snowmelt from thick snowpacks in the mountains during the dry spring and summer months to supply water. Rainfall does not contribute to snowpack buildup, and although it can quench the area temporarily, it does not provide water for the drier months. This creates water shortages during months of peak demand. It is believed that the recent California drought was made worse by record low levels of snow in the Sierra Nevadas. The Sierra snowpack is an important source of water for California, and the winter of 2015 saw record 500-year lows for snowpack levels, increasing the pressure on the already water-stressed state (Belmecheri et. al, 2015).
One consequence of droughts and, drier, hotter climate patterns is the more frequent occurrence of larger, more destructive wildfires, especially in ecosystems that rely on smaller-scale seasonal wildfires. More heat and less precipitation dries out the forests, which provides fuel for more damaging wildfires. For example, the recent fires in the Pacific Northwest of the United States were not directly caused by climate change (they were ignited by humans). But the increasingly hot and dry conditions allowed the fires to spread over a greater area and burn much hotter than usual. The intensity of the flames make the fires much harder to control, and scientists theorize wildfire season will only get worse in the coming years as temperatures continue to rise.
To summarize both this installment and the previous one, scientists cannot conclusively state that the recent natural disasters are directly caused by climate change. However, there is mounting evidence that extreme events like Hurricane Irma and the Pacific Northwest wildfires will become more prevalent in the coming decades as the world grows warmer. In contrast to many climate change impacts like ocean acidification or melting sea ice, the effects of these disasters are immediately tangible – preliminary estimates show Hurricanes Harvey and Irma caused around $200 billion in damages, as well as impacting the lives of millions of people. Wildfires currently threaten hundreds of homes and are causing thousands of evacuations. In South Asia, floods have already killed hundreds of people and displaced many more. It wouldn’t take an economist to say that more of these kinds of events in the future would continue to cause unfathomable amounts of damage.
Causes of Drought: What’s the Climate Connection? (n.d.). Retrieved September 27, 2017, from http://www.ucsusa.org/global_warming/science_and_impacts/impacts/causes-of-drought-climate-change-connection.html#.Wcr9HsiGPIW
Belmecheri, S., Babst, F., Wahl, E. R., Stahle, D. W., & Trouet, V. (2015). Multi-century evaluation of Sierra Nevada snowpack. Nature Climate Change, 6(1), 2-3. doi:10.1038/nclimate2809
Bernton, H. (n.d.). Northwest forests will get more and bigger wildfires with climate change. Retrieved September 27, 2017, from https://phys.org/news/2017-09-northwest-forests-bigger-wildfires-climate.html
Allen, K., & Davis, M. (n.d.). Hurricanes Harvey and Irma may have caused up to $200 billion in damage, comparable to Katrina. Retrieved September 27, 2017, from http://abcnews.go.com/US/hurricanes-harvey-irma-cost-us-economy-290-billion/story?id=49761970