Sierra Nevada mountains covered in snow. Photo: NAWCWD

By Bryan Walsh
17 June 2013

(TIME) – While the national government remains slow to deal with climate change, many cities have been moving ahead. Why the difference? Well, cities tend to be more homogenous politically, which makes any kind of decisive action easier to push through. But the real reason is that city managers know that they will be the first ones forced to deal with the likely consequences of global warming: rising sea levels and flooding, deadly heat waves and water struggles. New York City didn’t just come out last week with the most comprehensive climate adaptation plan in the world because Mayor Michael Bloomberg is a global warming believer. The experience of Hurricane Sandy last year—which cost the city some $20 billion—was instructive. Even in the absence of warming, growing population and property values will put major cities on the front lines of extreme weather. Add in climate change, and it could get ugly.

Just ask Los Angeles. The City of Angels has struggled with the basic fact that it is a desert metropolis since its founding. (Just watch Chinatown.) The first three months of 2013 were the driest for California on record, and there’s no relief in sight. Now a new study from the University of California-Los Angeles suggests that the local mountain snowfall—vital for water supplies—could fall 30 to 40% below 2000 levels by midcentury, thanks to global warming. And if emissions don’t decline and warming is worse than we expect, more snow will vanish, even as greater L.A. continues to grow.

In the business-as-usual scenario—a climate science term for a model that assumes greenhouse gas emissions keep growing without any effort to slow them—snowfall levels could fall 42% by midcentury, and over 60% by the end of the century. Here’s lead author Alex Hall of UCLA in a statement:

The mountains won’t receive nearly as much snow as they used to, and the snow they do get will not last as long … We won’t reach the 32-degree threshold for snow as often, so a greater percentage of precipitation will fall as rain instead of snow, particularly at lower elevations. Increased flooding is possible from the more frequent rains, and springtime runoff from melting snowpack will happen sooner. [more]

Why Dwindling Snow—Thanks Largely to Climate Change—Might Dry Out Los Angeles

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