Nevertheless, I have trouble with the most-newsworthy projections of the study (the ones that happen to fall outside John's specialty) regarding the climate changes at Lake Tahoe over the next century:
About 55 percent, on average, of the precipitation at lake level in Tahoe now falls as snow. By 2055, the study predicts snow will drop to about 45 percent – and to just 30 percent by the end of the century.Since global warming is expected to be concentrated in polar regions, the first-order climatic effect should be warming, with a retreat of the jet stream farther north. In other words, the northern Sierra should become more like the southern Sierra. But snowfall is still plentiful in the southern Sierra, so why the long faces here?
The result: a shorter ski season, and perhaps a spring without snow-capped peaks ringing the lake, said Robert Coats, lead author of the study and a visiting scholar at UC Davis.
"We're looking at a shift from snowfall to rainfall, increased melt rate, and earlier melt," Coats said. "Once you lose the snowpack, then you lose the late-spring water supply. So drought could begin earlier in the year."
I've started looking at the report itself, and I'm struck at what a strong, lower-precipitation impact they are forecasting. They put a lot of faith in their GCMs, but I can't help but wonder if weaker wintertime precipitation might mean stronger summertime precipitation from a stronger Southwestern monsoon. These days, the monsoon reaches the Tahoe region only imperfectly in summer, but the retreat of the jet stream might change that balance. And even in winter, you might see more activity from cutoff lows than you do today. Just because the jet stream retreats it doesn't mean it stops raining altogether.
I'll start looking at this interesting question in more detail....
No comments:
Post a Comment