January 05, 2023

The End of the Current California Drought

 The multiyear meteorological drought over California is rapidly ending.

Considering the enormous precipitation...both rain and snow...during the past month, coupled with the extraordinary precipitation predicted during the next ten days, the precipitation situation over the Golden State has been rapidly and radically altered, with good expectations for a refill of the major reservoirs serving the state.

Let me show you the data....and you can decide.

Some Perspective

As shown in the climatology of annual precipitation shown below, much of California is quite arid, with much of the Central Valley and southeast CA getting less than 10 inches are year (about 1/3 of the state).  Another third of the state (the southern coastal region, portions of the central valley, and northeast CA) get less than roughly 25 inches.   Only a small (about a quarter) portion of the state enjoys more than 40 inches a year,  encompassing the high terrain of the Sierra Nevada and the mountains of NW California).


There is a reason the Spanish did not move into California for a few hundred years--the place was too arid for agriculture.    Today, California supports a huge population and massive agriculture, depending on an extensive reservoir system, the ability to move huge amounts of water southward, and the (irresponsible) tapping of underground aquifers.

California's annual precipitation has always been hit-and-miss, and often unreliable.  The reason is that California is usually south of the main precipitation-bearing jet stream, with a majority of the rainfall coming from periods in which either the jet stream pushes equatorward or a potent atmospheric river pushes into the region (like right now).

A few years of "drought" followed by a few years of heavier precipitation (and often flooding) is the usual situation for California, something illustrated by the informative figure below from UC San Diego/Scripps showing the total water storage (reservoirs plus snowpack) since 1970.   

Not much long-term trend...but multiyear periods of more and less water.  The last few years have been a dry period.

The Big Turn Around

It appears that we are in the midst of a major turnaround in California's water fortunes.

The large-scale weather pattern shifted in December and moisture has been streaming into California, producing huge amounts of rain and snow.    Below are the precipitation totals for the state for the past month produced by the National Weather Service.  Over twenty inches in the higher terrain, with some locations reporting 25-35 inches.  Even lower elevations in the northern part of the state have received 5-10 inches.  San Francisco, for example, received 5.46 inches in 24 h, the second greatest 1-day total in a 170-year record.  Wow.


Considerable flooding has occurred around the State.  

The latest forecasts predict huge amounts in the future.  Below is the latest 10-day precipitation forecast by the European Center model.  Just stunning.  The whole state gets plenty of precipitation, but the stand out is the northern portion of CA, where large areas get more than 15 inches.  Lots of the state gets more than 8 inches.


Forecasts beyond ten days (less reliable, of course) are also wet. Furthermore, La Nina, which tends to make California dry, is now weakening and is predicted to weaken further.

Is the California Drought Ending?

The trouble with predicting the end of the drought is that it can be defined in many ways.  A big issue is the period that one is talking about.

For shorter periods, such as for the water year starting on October 1, the drought is arguably over and will certainly be over in ten days.  Rivers are flooding and the ground is saturated over much of the state (see the current status of the river from the USGS below, blue and black dots are rivers WAY above normal).


The current precipitation departure from normal for the water year (again, since October 1) is above normal for two-thirds of the State, and the predicted precipitation during the next week will extend the normal to above-normal precipitation to the drier northwest side of the State.

 California's current snowpack, critical for maintaining river levels during the spring and summer and for filling reservoirs, is far above normal.  As shown by the latest data, the snowpack is now 142-203% of normal (light blue shows climatological conditions, dark blue line is this year).  Some areas are now at record snowpack levels.


The Reservoirs and the Long Period Drought

The dry conditions of the past few years, coupled with the continued large usage of water, resulted in dropping levels in California's reservoirs.  But this situation is rapidly improving.  Massive rainfall is rapidly raising reservoir levels and a huge snowpack will ensure large additional water.   

Considering the total of current reservoir levels and snowpack, the western Sierra reservoirs should be restored to normal levels (see below). Even without additional heavy rain periods.


The dry northern reservoirs are rapidly increasing, and with heavy precipitation the coming week, should push reservoir levels to near normal by the end of the month.


Consider the huge Lake Oroville Dam in northern CA (below).  Rising rapidly.


Finally, consider the cumulative precipitation at San Francisco for the past two years.

Brown indicates normal accumulation and green was the actual precipitation.  During the past two years, the cumulative actual precipitation fell behind normal, but you can see that we have almost caught up to normal, and I suspect exceed normal within the next 10 days.  Other California observing locations are similar.


Summary

After a dry few years,  a switch to a very wet pattern is rapidly ending the current and cumulative deficiency from normal of California precipitation.  The ground is saturated, rivers are flooding, and there is good reason to expect that the reservoirs will fill to normal levels (some already there).  The "D" word should probably be dropped.

As an aside, one should note that groundwater levels continue to decline, but that is really the result of unsustainable drawdowns of aquifers by agricultural and other interests, not a change in the climate.










41 comments:

  1. From the Jan 4 2023 issue of the Weekly Weather and Crop Bulletin:
    Jan 1 2023 California soil moisture:
    Top 5% short,45%adequate,55%surplus
    Subsoil 5% short,45% adequate,45% surplus

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  2. I couple weeks ago, I heard one so-called expert say. "It will be years before we are out of this drought" Huh? I understand that a single storm will never make a drought go away, but at some point...

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  3. Cliff, our snowpack is slowly declining are long range models showing any more mt snow on the way?

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    1. Cliff may be clairvoyant, but most of us are not. You might be asking about CA or WA.
      You might be asking about '22/23 or the last 30 years.

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    2. @tim Yes, models have moisture/snow returning to WA mountains soon.

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  4. Thanks Professor. This is good news. I’ve tried to determine from USDA’s water reports if the Colorado water basin is similar, but a layman is no match for the data, and apparent inconsistencies. If you find it of merit maybe you could address that matter as well. But I understand the constraints if you don’t.

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    1. The Colorado River basin is also running above normal as a whole for this time of year, but only marginally so. Nothing like what CA is experiencing.

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    2. Thanks. That’s one conclusion I drew from one of the sites I visit. The other site seemed to indicate that the basin was still below normal. 1.https://www.nrcs.usda.gov/wps/portal/wcc/home/quicklinks/states/colorado/products 2. https://www.usbr.gov/lc/region/g4000/24mo.pdf 3. https://www.nrcs.usda.gov/wps/portal/wcc/home/quicklinks/states/colorado

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  5. Is this pattern shift connected to the warming of surface and subsurface water in the equatorial pacific as La Nina begins to wind down?

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  6. The NY Times, among others, is saying that climate change is partially responsible for the onslaught of rain in California. What do you say?

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  7. Oh, yeah. These people. "It's going to take years and years and years". The truth probably lies in the middle https://www.theverge.com/2023/1/5/23540720/california-storm-rain-snow-bomb-cyclone-atmospheric-river

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    1. That article sounds similar to this one: https://www.vox.com/science-and-health/2023/1/6/23542194/california-atmospheric-river-flood-drought

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  8. i'm confused, cliff. you're saying, "groundwater levels continue to decline, but that is really the result of unsustainable drawdowns of aquifers by agricultural and other interests, not a change in the climate." but wasn't the reason for drawdowns demand for water caused by decades of low precipitation which can be attributed to climate change?

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    1. Unfortunately even in normal or wet years, CA uses massive, unsustainable amounts of ground water. In a NORMAL year, 40% of CA water comes from groundwater. That increases to about 50% in a dry year. So low groundwater is not a climate change problem but a water usage problem

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    2. Which, in turn, is a population problem. Forty million people living in a mostly desert state doesn't make a lot of sense to me unless the food can be grown elsewhere and they are catching fish for protein. Which probably can't be sustained either. Maybe just graze cattle in Central Valley and don't plow...

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    3. Not to mention miles and miles of open irrigation ditches, agricultural practices like plowing and destruction of vegetation with herbicides, all which destroy water-retentiom properties of soil

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  9. Good post, thanks Professor Mass. What do you think this means for the Colorado River system? Though the Cali reservoirs don't have much long-term trend, Lake Mead and Lake Powell *do* have a significant long-term trend down.

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    1. Not much. Sierra Nevada doesn't feed into the Colorado River. Very little of this moisture is actually making it past the Sierra's into Colorado basin.

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  10. Prof Mass, do the CA rains have any impact on the western half of AZ? Specifically, rains that will help the desert wildflowers this spring?

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    1. AZ has already had a couple good rains, including New Years day. Somebody told me the hill-slopes are turning green as a result

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  11. Again with the scare quotes on the word drought. How do you write such a lengthy and extensive post about ongoing drought in CA and yet still feel the need to imply that there never was a drought? Or is the use of "drought" meant to convey something other than suspicion about the veracity of the drought?

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    1. Is it really a drought when it is entirely consistent with historic weather patterns?

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  12. It's pretty clear that an above average snowpack is going to pay dividends for months to come, but I'm curious how much these deluge conditions help the lowlands.It seems like there's so much rain that the vast majority is just going to run off into the ocean. How much more effective is steady precipitation for improving drought conditions than downpours?

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    1. The mountain precipitation is what counts.....and that includes snowpack. The runoff and meltoff from the mountains help fill the reservoirs. It can help to moisten the soil and temporarily reduce water usage, of course.

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    2. Wasn't prop 1 passed 2014 in California, money for building new reservoirs for increased storage capacity? Nothing built yet because of? Over regulation? https://news.yahoo.com/2-7-billion-bond-fund-110000548.html

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  13. You should read the Washington Post article that addresses questions about the drought ending to those people who are responsible for managing and monitoring California's water. They only go so far as to suggest that this event is a "good start" but will not, for a number of reasons say the drought is over.

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    1. Why should I read that rag?

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    2. To learn more about 4 kinds of drought, how they are monitored and more, I hope you'll read https://gardenprofessors.com/monitoring-and-reporting-on-drought-conditions/. Really interesting l, objective info.

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  14. Beyond these extremely rare storm events, any discussion of the California desert's water management should include the managed release of water from the reservoirs for various reasons unrelated to water consumption. From what it appears, they release water based on a very crude, non forecasted formula. This would seem to be inherently wasteful. Also it would seem that water supply in itself is not the constraining factor as much as reservoir capacity. The WaPo article cites various expert assertions, but is any of that backed up by verifiable, public data? How are we to know the existence and significance of earlier snowpack melt, increased soil moisture evaporation and so on? I have one other bone to pick, which is obsession with variation from the mean. How are we to know if a weather event's variation from the mean is significant if the variation of the past observations is not disclosed? Everyone from the TV weatherperson - who on a daily basis frames the weather as "good or bad" depending on whether it's above or below the average - to discussions in the media about weather and climate, seem to be built on an assumption that a weather event's variation from the mean is a problem.

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  15. Reference for my previous comment https://www.cbsnews.com/sacramento/news/getting-answers-why-are-dams-releasing-water-in-a-drought/

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  16. Our stupid California politicians and bureaucrats preferred to build a railroad to nowhere rather tan build more reservoirs and other water containment facilities, which could have alleviated the threat of drought. They should be held accountable.

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    1. Unfortunately, there is a long list of mismanaged items for CA politicians, but as the last vote showed, accountability won't happen.

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  17. The great tragedy in this current situation is that so much of the water scarcity problems for CA could've been easily alleviated if the state had accepted the recommendations from the Army Corps of Engineers back in the 70's and built addtional reservoirs, particularly in southern CA. Much of the groundwater aquifier drainage could have been prevented, along with other water issues. But not only did the Governor at that time rejected their advice, the wise citizens of the state actually reelected him decades later. SMH.

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    1. It seems to me that scarcity of a resource is one pathway to crisis, and crisis is a pathway to political power. So the great irony is the politician depends on crisis while ostensibly presenting themselves as solvers of the crisis. If the above ideas are axiomatic, we should perhaps be more skeptical.

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  18. Not so long ago, so another flooding event like this is conceivable. https://en.m.wikipedia.org/wiki/Great_Flood_of_1862#:~:text=The%20Great%20Flood%20of%201862,and%20continued%20into%20January%201862.

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  19. One thing that is often overlooked by these "the drought is over" blogs is the political realities and necessities of drought declarations. Farmers will continue to suffer for years because of the past effect of years of drought. Even if a drought may be potentially over from a meterological sense, the lasting effects and need for help from government agencies (FEMA, USDA, etc.) to address those effects last longer than the recent rains. When folks don't understand this very important distinction between the end of a drought from the meterological sense and the governmental/political sense, you kick up fights that are unwarranted. I'd love to see a blog from you that actually explains why a drought declaration remaining in place after the rains have come is a necessity for those who suffered through the drought and continue suffering for years after the rains come.

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  20. My father wrote a book in the late 1950's on California rangelands and in it he documented for the first time in one place much of California's historical flood-drought cycle, based on writings from Spanish explorers and very early ranchers. The default climate of California is (and always has been since humans have been around) dry, punctuated by extremely (and relatively rare) wet years. These wet years can be beneficial, obviously, but at the extreme can be disastrous. He documented evidence of droughts in the early 1800's so severe that early ranchers drove livestock into the ocean so that remaining forage could be saved for horses, and another period where it might not have rained to any degree in the southern half of the state for perhaps 2 years. The legendary 1861-62 year broke a 20 year drought, and the next two years after that "Megaflood" were "Megadrought" that further decimated the early ranching industry in the state. The big droughts in the early 1800's were punctuated by another documented "Megaflood" in around 1810. That is the way it works...big years often break droughts, and big years are often followed up by lousy ones. And once every 100-200 years there is something really big, with enormous negative impacts to the state. Daniel Swain believes that the next big flood will be due to (or turbocharged by) CC and will happen in an El Nino year. Others disagree. I don't think it is as simple as saying the next big flood will be worse simply because somewhat warmer air holds more water vapor. It seems far more complicated than that, since a "Megaflood requires both warm and cold storms, with the cold ones delivering lots of low level snow that is easily melted with warm rain. But hey, what do I know?

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