Monday, February 06, 2017

It's raining again ...


I should be thrilled after years of California drought, but I confess I'm getting a little sick of this. Running in the rain is a lot less fun than running in dry weather. And when there is lots of water, there is also mud, another deterrent ...

But this is good -- the drought is finally broken, right? I decided to put some brains cells into finding out.

Here's the good news according to the California Weather Blog:

Most of the state currently sits at or above 150% of average for the Water Year to date, and some spots are well over 200%. This marks the wettest first half of the rainy season in many years, and perhaps the best news is that much of this water has actually fallen in frozen form as snow in the Sierra Nevada. In fact, the current snow water equivalent in California is the highest in 22 years–since the memorable storms during the winter of 1995.

Why should we be glad that so much of the precipitation takes the form of snow? Existing water systems depend on winter snows, not run off.

The melting of the spring snowpack determines how much water feeds critical reservoirs in 11 Western states. That water helps sustain Phoenix, Los Angeles, Las Vegas and other cities, as well as farms and mountain ecosystems, through hot, dry summers.

Yet the warming climate points to less and less snowpack in the mountains of the West -- even if we don't have drought conditions. The Weather Blog explains how this will play out in the heavy rains of this year.

... this prodigious mountain snowfall has not occurred because it has been particularly cold. In fact, data show that temperatures to date have–for the seventh consecutive winter–been above average, though not by as wide a margin as during recent record warm winters. ... It’s pretty clear that the huge influx of Pacific moisture in recent weeks, combined with “just cold enough” temperatures, was the real driver behind this fortuitous snowpack turnaround.

This recent experience is interesting in light of expected future changes to Sierra Nevada snowpack as California’s climate continues to warm. Big snowfalls like the January 2017 event will still sometimes occur even in a much warmer climate, but future storms that might historically have been “just cold enough” will instead be “not quite cold enough,” and associated precipitation will be much more likely to fall as rain, rather than snow.

In fact, scientists foresee a drastic rise in the elevation at which rain becomes snow over the next century.

The snow line will rise by an average of 950 feet across six Western mountain regions by century's end. The study, by a team of University of Utah scientists, was published online in the journal Geophysical Research Letters last month.

And warming conditions will do more than lower water run off.

Researcher Alex Hall used a complex computer model to look at what would happen to the Sierra Nevada mountains if [carbon] pollutants kept entering our atmosphere at the current rate.He found that by the end of the century, average temperatures could climb by 7 to 10 degrees Fahrenheit and average land area covered by snow could fall by 50 percent.

Even worse, this reduction in snow would likely fuel more warmth, since as snow melts it exposes land. Since land isn’t as reflective as snow, it absorbs more heat and adds more warmth to the area around it. Hall said it’s a feedback loop that spells trouble for the snowpack.

Sure would be nice to have a government that was trying to reduce carbon emissions and plan for our dryer future. We have something like that in California, but in Washington the oil barons reign ...

Resist and protect much. The quality of the lives of those who come after us depend on what we do now.

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