Friday, May 18, 2018

Wet Spring

After another very dry winter, Yosemite has had a bit of recovery with a wet spring. We had warm storms in March and April and are now enjoying a string of about 10 days of cool, cloudy afternoons. The first weekend of April we had the markedly unusual experience of a very late, warm, winter-scale storm. This atmospheric river brought high elevation rain instead of snow, a flood forecast, and a successful pre-emptive evacuation of Yosemite Valley. Sure enough, the Merced River came up through the campgrounds, over the roads, through Housekeeping Camp, and filled the meadows. NPS has nice footage online. There's a persistent myth that these 'Pineapple Express' storms melt a lot of snow, but they really don't. It's the high elevation rain over thousands of acres of bare rock and thin soils that fills the river. This flood event wasn't from a 'monster' rainstorm, just a pretty big storm up high. Lower elevation side streams barely rose, compared to what the river did.

Because of the poor winter and the late-season rains, our springtime runoff peaked a month ahead of normal. The Merced and the waterfalls are already declining in volume, especially with the cloudy conditions we've been having. The clouds are delaying our minimal runoff a bit, which will help waterfalls last and forests to stay watered a bit further into the summer.

The park is still busy felling hazard trees, the small portion of our dead trees that might fall on people/roads/infrastructure. This year's below-average precipitation and above-average warmth will continue to stress Sierra forests (over-thick with trees due to decades of fire suppression) and we'll see more of the weak trees succumb to native bark beetles. Despite changes in Washington, D.C., the NPS in Yosemite is sticking with science and is not dodging the reality of climate change in its training of new rangers. The climate IS changing, it's changing NOW, in ways more rapid than ever, it is because of OUR hydrocarbon use, and it'll have serious consequences for US. It's disappointing that some political leaders think they know more than NASA or the National Academies of Science. Among other things, our fire season is longer, more severe and is costing us all more money to deal with. I'll be heading up to Lyell and Maclure Glaciers with Yosemite Conservancy groups in August and I expect to see those small ice bodies closer to leaving Yosemite entirely glacier-less.

Luckily, because we are causing the current rapid changes in climate, we should have some influence over it. Let's work to reduce our mistake and bring back snowy winters.

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