Dry December
Dec. 28th, 2020 03:57 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
canyonwalkerIt's been a fairly dry December here in the Bay Area and, more broadly, in California. I was thinking about that today as I recalled how we've only had a few, light rain showers in the past month. Indeed, the numbers bear out my anecdotal observation: figures compiled by Golden Gate Weather Services (retrieved 28 Dec 2020) show San Jose has gotten 1" of rain so far this season compared to an average of 5" by this time. Most areas in the state are under 1/3 season-to-date averages and some, particularly in Southern California, are below 10% of normal.
California is not unique in this regard. It's part of a weather pattern called Mediterranean Climate (Wikipedia link) or dry summer climate. This map from Wikipedia shows where in the world it occurs:
Obviously the name comes from this being the climate pattern around the edges of the Mediterranean Sea. It also holds for most of the west coast of the US— including the metro areas of Los Angeles, San Diego, Orange County, San Francisco, San Jose, Sacramento, Portland, and Seattle— and a variety of other regions around the world. As I said, pretty much all our rainfall comes in a period between November and March. Thus when it's late December and there's barely been any rain the past two months it's time to be concerned... about drought.
Is it time to press the panic button about drought?
Is it time to press the panic button?Not really. ...Well, not yet, anyway. Just because the rain season has gotten off to a slow start doesn't mean we won't catch up later. Years of living in California have shown me that "normal" is a statistical average, not a month-by-month plan one can count on. For example, the first winter I lived in California there was a deluge of rain in December and January, then practically nothing the rest of the season. Other years we've had a dry month in the middle of winter and then rain into the Spring.
All that said, getting off to a dry start this winter is concerning news. It increases the chance of this being another not-enough-rain season. As we've gotten less than average annual rainfall I think, what, 6 of the last 8 years? Drought isn't just a threat, it's already a reality. We need more rain to push the danger away.
UPDATE: The 2020-2021 rain season turned out to be another dry one, not just in California but across much of the American West. Rivers and reservoirs are drying up. Consider the panic button pushed.
Why it Matters: Mediterranean Climate
California has beautiful, dry summers. The flip side of this is that we have wet winters. Pretty much all our rainfall comes in a period between November and March.California is not unique in this regard. It's part of a weather pattern called Mediterranean Climate (Wikipedia link) or dry summer climate. This map from Wikipedia shows where in the world it occurs:
Obviously the name comes from this being the climate pattern around the edges of the Mediterranean Sea. It also holds for most of the west coast of the US— including the metro areas of Los Angeles, San Diego, Orange County, San Francisco, San Jose, Sacramento, Portland, and Seattle— and a variety of other regions around the world. As I said, pretty much all our rainfall comes in a period between November and March. Thus when it's late December and there's barely been any rain the past two months it's time to be concerned... about drought.
Is it time to press the panic button about drought?
Is it time to press the panic button?
All that said, getting off to a dry start this winter is concerning news. It increases the chance of this being another not-enough-rain season. As we've gotten less than average annual rainfall I think, what, 6 of the last 8 years? Drought isn't just a threat, it's already a reality. We need more rain to push the danger away.
UPDATE: The 2020-2021 rain season turned out to be another dry one, not just in California but across much of the American West. Rivers and reservoirs are drying up. Consider the panic button pushed.
