Drops of Change: Wildfires Wreak Havoc on Western US Watersheds

This post is part of a monthly series called “Drops of Change” by the North American Youth Parliament for Water (NAYPW), a chapter of the World Youth Parliament for Water (WYPW). For more information on the NAYPW, you can explore their website or contact NAYPW at outreachnaypw@gmail.com.

Written by Katie Wampler,  MS candidate in Water Resources Science, Oregon State University

7 September started like any other day in Corvallis, Oregon in the Western US - I woke up, got a new model run going for my research project, and tried to check items off my to-do list. 

Later, I got an emergency alert about a red-flag warning and high fire danger due to dry conditions and strong winds from the East, which are uncommon in the summer western Oregon. 

By 7 pm the sky was dark and hazy, and the smell of campfire drifted through my windows. We got another emergency alert: don’t call the emergency phone number unless you actually see flames. The smoke was blowing in from the Lionshead Wildfire on the other side of the Cascade  Mountain Range. The sky was orange. 

A smoky, orange sky in Corvallis, Oregon, US during the September fires in the Western US.

The next day brought news that the Beachie Creek Fire, which was around 500 acres large the day before, had exponentially spread and was now closer to 100,000 acres, and the Holiday Farm Fire, which started sometime on 7 September, had spread overnight to 37,000 acres. While we were dealing with our own megafires, news of fires in elsewhere in the Western US drifted in, photos of red skies made headlines, and people wondered, is this our new normal? 

Interactive map of wildfires in the Western US : The data initially shown corresponds to current fires. The larger the icon, the greater the daily acres burned. Click the arrows in the top left corner to explore historic wildfire data.

In the US, the annual number of wildfires since 2009 has been fairly consistent. However, the number of acres burned has increased, especially in California. This is what we’ve started to see: huge, destructive, and severe wildfires that can throw landscapes into chaos. This trend is often attributed to climate change causing warmer temperatures, earlier snowmelts, and drier conditions.

While the number of wildfires (black line and right axis) have not increased, the area burned (colored bars and left axis) has increased since 2009. This supports the finding that fires in the the Western US are getting more intense.

Clearly wildfires cause damage - even low-intensity fires do - but one type of wildfire damage that often gets overlooked is damage to our water resources. One-third of the world’s largest cities rely on forests for their drinking water and, in US’s Northwest, 75% of the water supply comes from forested regions. Typically the water is fairly clean and requires minimal treatment. It has been estimated that, worldwide, the natural storage and filtering processes of forests has an ecosystem services value of $4.1 trillion a year. So what happens when those valuable, hard-working forests burn?

The 1996 Buffalo Creek and 2002 Hayman wildfires burned in the forests near Denver, Colorado, a major city in the Western US with a metropolitan area population of almost 3 million people. The fires altered the landscape so that when flash floods came through, masses of sediment were carried from hill-slopes, and fire debris was deposited in the reservoirs storing drinking water for the city. It cost over $27 million to repair the damage, dredge sediment from the reservoirs, and heal the landscape to prevent future events. 

When it comes to drinking water, there are three major concerns following a wildfire: (1) dissolved organic carbon, (2) suspended sediment, (3) nitrogen and phosphorus. Organic carbon can lead to carcinogenic disinfection by-products which are costly and difficult to remove. Suspended sediment can clog filters, fill reservoirs, and make disinfection less effective. Nitrogen and phosphorus are often limiting nutrients in aquatic ecosystems, so increases in these can spur growth, including toxic algae species which can contaminate drinking water sources. 

Burn scars from a recent fire in the Western US.

Wildfires consume vegetation, which can alter nutrient cycling, allowing more leaching to streams. The loss of vegetation and its anchoring roots means that erosion is often increased after a wildfire, especially on steep slopes. Water flows are also often altered. The heat can cause hydrophobic layers to form and ash to fill soil pores. Typically, burnt areas see higher amounts of runoff, which can bring carbon, sediment, and nutrients into streams. The increase in runoff can also make streams flashier, meaning that changes in the source water quality can happen quickly, making treatment even more challenging. 

Climate change is likely to bring warmer temperatures and dryer conditions which will likely mean more large fires. We’ve already started to see this trend in much of the US. However, there’s a lot of uncertainty in future precipitation amounts and intensities.  Increased high intensity storms could exacerbate water quality issues, whereas drier conditions may mute water quality responses. 

Wildfires are unpredictable. It’s hard to predict how large a given fire will get and how severely it will impact the landscape. Additionally, wildfire-water quality impacts vary widely in the literature. This can make it challenging to prepare for, much less prevent those impacts. We need to better understand the landscape characteristics that cause this variability in stream chemistry.  This knowledge would allow targeted pre- and post-wildfire treatments in areas sensitive to wildfire-water quality impacts. Mitigating source water quality issues can be extremely expensive. What if we could significantly reduce those issues with targeted treatments to the especially vulnerable sub-basins within a watershed?

It’s now late September - the fires are slowing down, the air quality is improving, and the sky is no longer orange. But even as things get back to what appears normal, don’t forget that the water coming from those burn scars will likely be anything but normal for many years to come.