Two stories are filling up my Twitter stream this morning. One is about Horsetail Fall, which, at this time of year, glows orange with the setting sun, and the other is about the alpine chipmunk, a high-elevation resident of Yosemite. What could these two stories possibly have in common (other than Yosemite)?
First, a little background.

Horsetail Fall is one of many tiny, barely noticeable waterfalls in Yosemite Valley, especially when compared to the nearby waterfalls that are much larger and more famous. It flows off the eastern side of El Capitan during winter and spring, and is positioned in just such a way that the setting sun colors it orange in mid to late February (if there’s enough water and not too many clouds). The effect is unusual if not unique, and very cool to see when conditions are right. It’s even more popular because of its comparison to the Fire Fall. (Beginning infrequently as early as the 1870s and recurring on a more regular basis later on, until 1968, park employees would build a bonfire at the top of Glacier Point, then, as it got dark, they would slowly shove the embers over the edge, creating the Fire Fall.) The result was what looked like a glowing waterfall.) Horsetail Fall with the right light looks similar and, better yet, is completely natural.

The alpine chipmunk is one of the species of chipmunks that lives in Yosemite. As the name suggests, this chipmunk lives at the highest elevations of the park. A recent study found that the elevational range of the alpine chipmunk had shrunk (risen) by over 1,600 feet since the 1910s (when it was found as low as 7,800 feet). Since the 1910s, the average temperature in Yosemite has risen by over 5 F°. It’s safe to assume that rising temperatures have pushed these tiny, temperature-sensitive animals higher in elevation because the lower portions of their range have become too warm. Now that their elevational range is smaller, the amount of land they have to live in has shrunk dramatically. I’m not sure of the numbers, but a large portion of the park is at or above 7,800 feet, but only a small portion of the park is at or above 9,400 feet. With such a loss of  habitat, it’s no surprise that this study found that genetic diversity had declined significantly (making the population more susceptible to disease and less able to cope with further environmental change). With (relatively) extreme warming over many more decades, the chipmunk could eventually have its elevational range exist only in the sky, above the highest peaks of Yosemite. But, with loss of genetic diversity, it could become extirpated (locally extinct) much sooner.
So, what does this chipmunk story have to do with Horsetail Fall?

While many people (but hardly any scientists) argue over whether humans are at least partially the cause of climate change, climate change is an observable fact in Yosemite. The impacts of climate change are not limited to the alpine squirrel or some of the other plants and animals that could be impacted with continuing change. Climate change is slowly reducing the majesty of Yosemite’s waterfalls. As average winter snow level continues to rise over the decades, the area of Yosemite getting a snowpack will continue to decline, which means less snowmelt to feed Yosemite’s waterfalls. Spring runoff in Yosemite will be less dramatic (runoff following winter storms might be the best time to see waterfalls). With its tiny and relatively low-elevation drainage area, one of the first victims of this change will be Horsetail Fall, which might rarely flow, even in winter.

Climate change is not only shrinking the alpine chipmunk’s habitat, but also shrinking Horsetail Fall’s already tiny snowpack. When the alpine chipmunk becomes an endangered species, Horsetail Fall and its elusive orange glow may, like the Fire Fall, become just a memory.

 


Yosemite Nature Notes has some quite excellent videos about Horsetail Fall, snowpack, and climate change:

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