I was driving back from San Francisco to the South Bay in the early afternoon. Parts of the 101 were apparently closed off, so we took the 280, and saw several accidents along the way. Visibility was quite poor and the roads were very slippery. Haven't seen it this bad since I moved to the area about a decade ago.
To be fair most of that decade has been a state-declared drought (2012-2016) :) and I believe the interceding years were also usually low in terms of precipitation even though they didn't meet the formal definition of a drought.
I’m pretty sure it’s just that people are so inexperienced when it comes to wet roads that the slightest bit of loss of traction causes chaos.
I’m sure buildup of dirt and oil on roads that isn’t regularly washed off with rain makes things a little worse.
But like in Minnesota there are always tons of accidents during the first snow of the year. Then people remember how to drive in the snow and everything is fine for the next 40 snows.
Infrequent rain means when it does rain lots of oil floats to the surface and creates poor road conditions. That, and drivers are less accustomed to driving in rain. By comparison, here in Seattle light to moderate rain and people still drive at full speed. A heavy downpour will slow things down a bit.
Life long Bay Area resident here. This is absolutely the case. When I used to commute over HWY17 I started taking the day off on the first rain of the season because it was way too slippery to be safe. Corners that were safe enough at 55 in the rain normally people would spin out going 35.
I got curious about this and loaded the Met Office data your link cites into a spreadsheet. This particular dataset goes back to 1836, although the UK has data for rainfall from before that going back into the 1700s.
Plotting winter rainfall does indeed show a small trend towards wetter winters (r² = ~0.1). But the plot looks odd. Virtually all the trend comes from a step change starting around 1980. Since then the trend has been tiny (r² = 0.02). The trend from 1860 to 1980 is flat (r² = 0.0018). This doesn't look much like what you'd expect from a continuous process, which CO2 emission has been:
"As automated instruments were introduced across the synoptic network in the 1980s and 1990s the 5 inch gauge was still deployed alongside the tipping bucket gauge to continue a long consistent record of measurements for climate purposes. In recent years this practice has proved impractical and many automatic sites now only report rainfall amount from a tipping bucket gauge."
So around the time they start introducing automation to the network and switch to tipping bucket gauges, winter rainfall measurements go up a bit and then re-stabilize. Hypothesis: the old network that relied on manual measurements by volunteers was prone to under-measure in winter when people don't want to go outside.
What about summer rainfall? The cited atmospheric effect would presumably hold regardless of season as it's just about warmer air = more moisture in it. But here we see there's actually a slight downward trend, although yet again it's so trivial as to be irrelevant (r² = 0.0036). There is no change starting in the 1980s either, which would weakly support the idea of a problem with prior winter under-collection.
So it looks like not much is happening in this data. To sanity check that I grabbed a Met Office report on rainfall trends. It says:
"An analysis of annual, summer and winter rainfall observations by Jenkins et al. (2008)
shows that annual mean precipitation over England and Wales has not changed
significantly since 1766 when the records began"
If global warming is changing rainfall patterns it isn't having much effect, and to the extent small trends in the winter data do exist it's possible that the data set has been affected by methodology changes. Note that if such a problem does exist the common practice of only analyzing data since 1960 would yield a maximally biased trend, as the long period of absolute stability up until 1980 would largely be erased.
What about summer rainfall? The cited atmospheric effect would presumably hold regardless of season as it's just about warmer air = more moisture in it.
Is there any evidence that it holds in Summer or are you just assuming?
I was going off the quote in the OP which comes from the Guardian article which is credited to the Met Office. It dates from 2011 and says:
> A warmer atmosphere can hold more moisture
Nothing in that specific causal claim is dependent on season. If anything the obvious inference is that rains should be harder in summer and less so in winter. It isn't very important because as a sibling comment says, drier summers and wetter winters is long predicted via other mechanisms. Nonetheless, the article goes on to say that:
> So far, any impact that climate change may have had generally on regional rainfall cannot be distinguished from natural variations
So they seem to be agreeing with what I wrote above. Not much is happening in this dataset.
> What about summer rainfall? The cited atmospheric effect would presumably hold regardless of season as it's just about warmer air = more moisture in it. But here we see there's actually a slight downward trend
Yes, this is what scientists predict: wetter winters and drier summers.
Hard to pick a best, the palette changes quickly and it's all very weather dependent. March will be on the cold side and just starting to bloom, by June many will have dried up.
I went on a hunt after remembering some very heavy rainfall here in NZ and wanting to compare. That lead me to this record of 1.8m/71 inches in a day on Reunion Island. That’s a lot.
What are the odds that the “tipping-bucket rain gauge” was impacted by being repeatedly shook by the storm, triggering the counters — or some other source of error, fraud, etc.?
Is there data for cyclonic rainfall that might be modeled for similar to how this article titled “How can we call something a thousand-year storm if we don’t have a thousand years of climate observations” is?
Exactly. It must be measurement error. 1.8m across the kind of area that rains falls is a "scour everything down to bedrock" level of water. It just doesn't check out. When you get that much water in one place the results make the history books.
Mount Waialeale on Kaua'i supposedly received 683 inches in 1982[0], so perhaps it's not totally inconceivable that some other tropical place received about a tenth of that in a day?
I live in Utah County in Utah, also part of the American West. We have been getting so much moisture this season. Everyone's been talking about a decades-long drought and how it could kill off our farming but I'm starting to hope that we're coming out of it or at least that we'll have a nice respite. A few seasons back my trees died because there wasn't enough snow. This season nobody's trees are dying let me tell you that. So much snow and rain.
A real challenge for California is that the reservoirs are tuned for snowmelt rather than rainfall.
That is, snow hitting the Sierra and Cascade mountains (Shasta, Lassen) over the winter, then melting over the spring.
I don't know what temps are associated with this storm, or how the snowmelt will develop over the springtime, but a large deluge as rain hitting the reservoirs would 1) rapidly fill them and 2) require lowering the lake levels to manage further floodwaters.
This is one reason why climate change and warming is such a challenge for the Western US: its water management systems are tuned for colder weather patterns and not year-round warm rains.
If you want to get a sense for the scale of the flooding, KPIX CBS put out a video with a lot of shots, from the Mission to Fisherman’s Wharf, 101 and 280, Walnut Creek, San Ramon… wild to see flooding like this everywhere:
28 comments
[ 2.8 ms ] story [ 35.1 ms ] threadNone of that detracts from this of course.
This is one thing that surprised me when moving from NY (lots of snow) to SF.
Rain in SF seems to trigger traffic conditions similar to light snow or ice in the northeast.
I’ve always been curious what causes this. (My guess is people are slower to replace balding tires when there isn’t frequent rain or snow)
https://blog.response.restoration.noaa.gov/oil-water-and-dan...
I’m sure buildup of dirt and oil on roads that isn’t regularly washed off with rain makes things a little worse.
But like in Minnesota there are always tons of accidents during the first snow of the year. Then people remember how to drive in the snow and everything is fine for the next 40 snows.
> A warmer atmosphere can hold more moisture, and globally water vapour increases by 7% for every degree centigrade of warming.
https://www.theguardian.com/environment/2011/dec/15/climate-...
Plotting winter rainfall does indeed show a small trend towards wetter winters (r² = ~0.1). But the plot looks odd. Virtually all the trend comes from a step change starting around 1980. Since then the trend has been tiny (r² = 0.02). The trend from 1860 to 1980 is flat (r² = 0.0018). This doesn't look much like what you'd expect from a continuous process, which CO2 emission has been:
https://gml.noaa.gov/ccgg/trends/
This sort of sudden discontinuity raises the question of whether there was a methodology change at some point. A quick check shows that there was:
https://www.metoffice.gov.uk/weather/guides/observations/how...
"As automated instruments were introduced across the synoptic network in the 1980s and 1990s the 5 inch gauge was still deployed alongside the tipping bucket gauge to continue a long consistent record of measurements for climate purposes. In recent years this practice has proved impractical and many automatic sites now only report rainfall amount from a tipping bucket gauge."
So around the time they start introducing automation to the network and switch to tipping bucket gauges, winter rainfall measurements go up a bit and then re-stabilize. Hypothesis: the old network that relied on manual measurements by volunteers was prone to under-measure in winter when people don't want to go outside.
What about summer rainfall? The cited atmospheric effect would presumably hold regardless of season as it's just about warmer air = more moisture in it. But here we see there's actually a slight downward trend, although yet again it's so trivial as to be irrelevant (r² = 0.0036). There is no change starting in the 1980s either, which would weakly support the idea of a problem with prior winter under-collection.
So it looks like not much is happening in this data. To sanity check that I grabbed a Met Office report on rainfall trends. It says:
"An analysis of annual, summer and winter rainfall observations by Jenkins et al. (2008) shows that annual mean precipitation over England and Wales has not changed significantly since 1766 when the records began"
https://www.ofwat.gov.uk/wp-content/uploads/2015/11/rpt_com_...
If global warming is changing rainfall patterns it isn't having much effect, and to the extent small trends in the winter data do exist it's possible that the data set has been affected by methodology changes. Note that if such a problem does exist the common practice of only analyzing data since 1960 would yield a maximally biased trend, as the long period of absolute stability up until 1980 would largely be erased.
Is there any evidence that it holds in Summer or are you just assuming?
> A warmer atmosphere can hold more moisture
Nothing in that specific causal claim is dependent on season. If anything the obvious inference is that rains should be harder in summer and less so in winter. It isn't very important because as a sibling comment says, drier summers and wetter winters is long predicted via other mechanisms. Nonetheless, the article goes on to say that:
> So far, any impact that climate change may have had generally on regional rainfall cannot be distinguished from natural variations
So they seem to be agreeing with what I wrote above. Not much is happening in this dataset.
Yes, this is what scientists predict: wetter winters and drier summers.
https://wmo.asu.edu/content/world-greatest-twenty-four-hour-...
Is there data for cyclonic rainfall that might be modeled for similar to how this article titled “How can we call something a thousand-year storm if we don’t have a thousand years of climate observations” is?
http://www.climate.gov/news-features/event-tracker/how-can-w...
[0]: https://en.wikipedia.org/wiki/Mount_Waialeale
http://www.bom.gov.au/water/designRainfalls/rainfallEvents/w...
That is, snow hitting the Sierra and Cascade mountains (Shasta, Lassen) over the winter, then melting over the spring.
I don't know what temps are associated with this storm, or how the snowmelt will develop over the springtime, but a large deluge as rain hitting the reservoirs would 1) rapidly fill them and 2) require lowering the lake levels to manage further floodwaters.
This is one reason why climate change and warming is such a challenge for the Western US: its water management systems are tuned for colder weather patterns and not year-round warm rains.
https://youtube.com/watch?v=zCuKgorawck
Hoping people have managed to keep safe and dry.