Rim Fire Terrain Effects

Below is a picture of the Tuolumne River and Poopenaut Valley, just a mile or so below Hetch Hetchy’s O’Shaughnessy Dam. As you can see, the area burned rather lightly. What might be the reason for this area to survive, almost unscathed? I think there is a “micro-climate” at play, here. Most of this is Yosemite National Park.


Certainly, there are plenty of fuels, and California is in a historic drought. Firefighters did not “heroically” save this area from the flames. No management was done to make this area more resilient. Comparing this area to scorched places downstream, I think I have the answer. Farther downstream, the fires were enhanced by the nearly constant breeze, flowing down during the night and morning, and flowing up, with the heat of the day. Cold air sinks and warm air rises. This spot is pretty unique along the Tuolumne River. As the canyon turns from a glacier-sculpted valley into a V-shaped gorge, the cold air from higher elevations runs into this bottleneck, pooling up in this last valley, going downstream. Temperature inversions stay longer and stabilize the breezes, reducing fire behaviors.

One thing I did notice in this area was that many single digger pines were “selectively burned” as individuals. Those long slender needles were good at catching the small embers.

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