Sunday, December 21, 2008

Climate change and the snows of San Francisco Bay

I went on a run yesterday up at Castle Rock State Park, passing by my favorite waterfall/rock climbing spot. The creek surprised me by only trickling over the cliff at the same rate we'd see in late summer, despite all the stormy weather in the last week.

The potential explanation for the low flow was in patches on the forest floor around me - a lot of that precipitation came down as snow, some of it hadn't melted, and what had melted had slowly seeped into the ground instead of flashing into the streams.

A lot of non-locals don't realize the Bay Area gets snow every year (and even some local economics professors should know better). There are hundreds of thousands of acres in the Bay Area that lie above 2,000 feet in elevation, are virtually uninhabited, and get ephemeral snow for a few hours at a time each year. Tens of thousands of acres are above 3,000 feet, and snow can last for a few days at a time each winter, in addition to the ephemeral snow.

I've not seen anywhere how places like San Francisco Bay will be affected by the climate change switch from occasional snow to rare snow. I'd guess it will be a less-severe version of what will happen in the Sierras - higher winter stream flows, lower groundwater tables and lower summer flows. And while there'll be fewer hard frosts, there will also be fewer occasions where snow will protect plants from hard frosts.

And finally, fewer chances to bring some snow down to throw at your loved ones, like I did.

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