From a weather perspective, drought and historic wildfires became regular occurrences over the past several years. Exacerbated by climate change, these weather events are increasing in frequency and intensity. For the American West, and its cold-water ecosystems, these changing weather trends are having profound and interrelated impacts. Trout are vulnerable species, and thus often viewed as a canary in the coal mine species. When trout species are healthy, their ecosystems are generally healthy and functioning as they should. The opposite holds true, too. So, you may ask, “how will these record droughts impact trout and fly fishing?”
While many regions in the West are not experiencing drought, the majority is, which due to the interconnectedness of water has implications far and wide. Drought stresses both humans and natural resources, and intensifies competition for diminished water resources. Just look at California, for example, where water disputes are coming to a head and will result in contentious legal fights among a range of water users. And, “forecasts from the NOAA Climate Prediction Center suggest that conditions in the West won’t get better any time soon. According to NOAA climatologists, hot and dry weather is expected through late October.” Follow along, as we dive into the intertwined implications of “the worst drought in modern history.”
Reduced Snowpack
Droughts are not solely characterized by the lack of rain. Winter snow accumulation is an important component of droughts or lack thereof, especially in the mountainous West. A region’s snowpack, or compressed layers of snow and ice that persist for extended periods, represents a critical resource for cold-water habitats. Adequate snowpack provides cold-water habitats with consistent water supply and levels of dissolved oxygen, a necessity of aquatic life, throughout hot summers. Additionally, snowpack levels and the subsequent melt-off maintain a watershed’s moisture content, an important natural defense for wildfires. “So that snowmelt provides a gradual source of moisture, keeping those fuels in our forested areas wet later into the spring and early summer. And so when we don’t have the snowpack in place, when we have a subpar snowpack, those fuels are allowed to green up and actually dry out earlier in the year,” said John Abatzoglou of Cal Fire.
“Since 1915, the average snowpack in western states has declined by between 15 and 30 percent,” according to a 2018 Oregon Climate Change Research Institute study. As droughts persist, and snowpack decreases, some of our favorite trout fisheries in the West will become more and more threatened. Most species of trout require five to six times more dissolved oxygen when water temperatures reach 75 degrees compared to when they are at 41 degrees.” The impacts of diminished snowpack, low flows and warmer water temps, have serious impacts for trout and other cold-water fisheries and will continue being an essential consideration in fishery management processes in the future.
Stream Physiology
Not only can drought affect stream flows and levels, but its composition and level of habitableness are closely connected to prolonged periods of drought. For example, in drought conditions, consistent and cold water is scarcer, which has the effect of increasing stream temperature, stressing native aquatic species, and altering water composition.
When water temperatures rise and flows decrease, trout species are often forced to seek sanctuary in the system’s deeper pools. “If fish are forced to take refuge in decreasing and/ or isolated pools of water, they become easier targets for their prey, such as osprey and heron,” not to mention fishermen and women. Most trout anglers understand this, and many fly shops will tell you when local streams are too warm or low to sustainably fish.
The above example is obvious, but other stream impacts of drought are less mainstream, no pun intended, and more complex. When a watershed is experiencing prolonged and intense drought conditions, the surrounding land and dirt harden (worsened by intense wildfire), essentially creating an impervious surface that efficiently transport sediment–runoff. “Instead of water percolating into subsurface areas of the soil, most of the water directly runs off and flows into the streams. The excessive runoff has a lot of energy as it flows downstream, and it causes massive erosion events and carries huge volumes of sediment and ash into the stream channels.”
Sediment can have positive impacts for streams and rivers, including replenishing banks and sandbars or transporting nutrients downriver. However, sedimentation is more often viewed and interacts in aquatic habitats as a harmful pollutant. “Precipitation, flow and turbidity data revealed monsoon rain events delivered sediments into the Rio Grande and its tributaries from steep, severely burned hillslopes. The monsoon events caused acute and dramatic fish kills, where hundreds of trout were reported killed in one tributary in a single day event,” according to a water quality study on the Upper Rio Grande River.
Wildfires
As you’ve gathered by now–the impacts of droughts are incredibly interconnected and often exacerbate other impacts. Droughts leave higher elevations with less snowpack, which brings less cold water into a watershed, which has negative effects on trout and aquatic habitats. It also promotes and intensifies wildfires, which have harmful effects on stream and river environments. Last year marked dozens of record wildfires throughout the West, and this year may mark another “devastating fire season.”
While harmful sedimentation can occur in functioning watersheds, or those afflicted by drought, it is even more intense in areas scorched by wildfires. After a wildfire, the bare and hardened soil is amazingly efficient at transporting sediment and ash into waterways. “These ash-ladened flood events sometimes last for years and are often sufficient to wipe out any remaining fish. Ecologically, these events reset the entire stream system, the forest is essentially burned and then the entire stream network is change.”
In addition, watersheds that experience intense wildfires face harmful nutrient pollution. After a wildfire, in-stream nutrient levels–such as nitrogen, phosphorus, and potassium which feed plankton and algae–can skyrocket. “Excess amounts of these nutrients can cause algae blooms, which, when alive, decrease light penetration and, when dead and decomposing, decrease amounts of dissolved oxygen,” a requirement for trout and healthy streams.
Despite this year expected to be the worst drought in modern history and a devastating wildfire season, watersheds are remarkably resilient. Droughts and wildfires are not new phenomenons; they have occurred naturally for thousands of years. But what we are experiencing more recently are extreme weather events in comparison. Regardless, the affected watersheds have exhibited remarkable strength and restorative properties. For example, a 2018 study found that amid “notable short-term drought impacts to trout and salamanders in 2015, populations recovered to pre-drought conditions within two years in all but the smallest stream.” While this is a promising finding, droughts, wildfires, and all the connected impacts are becoming more frequent, longer, and stronger with climate change.
As drought conditions worsen this year, it is all the more important to consider your impact on hyper-stressed ecosystems. Pay attention to local fire warnings and, when in doubt, just don’t light that roaring campfire. Even little things, like a hot car muffler, can start a wildfire. Keep an eye on in-stream temperatures–if water temps are warmer than 67 degrees, STOP FISHING! Droughts, wildfires, and climate change continue to have complex and profound impacts on our waterways and environments. As anglers, it is important that we do our part to lessen our impact and protect our cherished fisheries and resources.
Cover picture courtesy of Inciweb.gov.
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