California ‘rain debt’ equal to average full year of precipitation


California's accumulated precipitation "deficit" from 2012 to 2014 shown as a percent change from the 17-year average based on TRMM multi-satellite observations. CREDIT NASA/Goddard Scientific Visualization Studio

California’s accumulated precipitation “deficit” from 2012 to 2014 shown as a percent change from the 17-year average based on TRMM multi-satellite observations. CREDIT NASA/Goddard Scientific Visualization Studio

A new NASA study has concluded California accumulated a debt of about 20 inches of precipitation between 2012 and 2015 — the average amount expected to fall in the state in a single year. The deficit was driven primarily by a lack of air currents moving inland from the Pacific Ocean that are rich in water vapor.

In an average year, 20 to 50 percent of California’s precipitation comes from relatively few, but extreme events called atmospheric rivers that move from over the Pacific Ocean to the California coast.

“When they say that an atmospheric river makes landfall, it’s almost like a hurricane, without the winds. They cause extreme precipitation,” said study lead author Andrey Savtchenko at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

Savtchenko and his colleagues examined data from 17 years of satellite observations and 36 years of combined observations and model data to understand how precipitation has varied in California since 1979. The results were published Thursday in Journal of Geophysical Research – Atmospheres, a journal of the American Geophysical Union.

The state as a whole can expect an average of about 20 inches of precipitation each year, with regional differences. But, the total amount can vary as much as 30 percent from year to year, according to the study.

In non-drought periods, wet years often alternate with dry years to balance out in the short term. However, from 2012 to 2014, California accumulated a deficit of almost 13 inches, and the 2014-2015 wet season increased the debt another seven inches, for a total 20 inches accumulated deficit during the course of three dry years.

The majority of that precipitation loss is attributed to a high-pressure system in the atmosphere over the eastern Pacific Ocean that has interfered with the formation of atmospheric rivers since 2011.

Atmospheric rivers occur all over the world. They are narrow, concentrated tendrils of water vapor that travel through the atmosphere similar to, and sometimes with, the winds of a jet stream. Like a jet stream, they typically travel from west to east. The ones destined for California originate over the tropical Pacific, where warm ocean water evaporates a lot of moisture into the air. The moisture-rich atmospheric rivers, informally known as the Pineapple Express, then break northward toward North America.

Earlier this year, a NASA research aircraft participated in the CalWater 2015 field campaign to improve understanding of when and how atmospheric rivers reach California.

Some of the water vapor rains out over the ocean, but the show really begins when an atmospheric river reaches land. Two reached California around Dec. 1 and 10, 2014, and brought more than three inches of rain, according to NASA’s Tropical Rainfall Measuring Mission (TRMM)’s multi-satellite dataset. The inland terrain, particularly mountains, force the moist air to higher altitudes where lower pressure causes it to expand and cool. The cooler air condenses the concentrated pool of water vapor into torrential rains, or snowfall as happens over the Sierra Nevada Mountains, where water is stored in the snowpack until the spring melt just before the growing season.

The current drought isn’t the first for California. Savtchenko and his colleagues recreated a climate record for 1979 to the present using the Modern-Era Retrospective Analysis for Research and Applications, or MERRA. Their efforts show that a 27.5 inch deficit of rain and snow occurred in the state between 1986 and 1994.

“Drought has happened here before. It will happen again, and some research groups have presented evidence it will happen more frequently as the planet warms,” Savtchenko said. “But, even if the climate doesn’t change, are our demands for fresh water sustainable?”

The current drought has been notably severe because, since the late 1980s, California’s population, industry and agriculture have experienced tremendous growth, with a correlating growth in their demand for water. Human consumption has depleted California’s reservoirs and groundwater reserves, as shown by data from NASA’s Gravity Recovery and Climate Experiment (GRACE) mission, leading to mandatory water rationing.

“The history of the American West is written in great decade-long droughts followed by multi-year wet periods,” said climatologist Bill Patzert at NASA’s Jet Propulsion Laboratory in Pasadena, California. He was not involved in the research. “Savtchenko and his team have shown how variable California rainfall is.”

According to Patzert, this study added nuance to how scientists may interpret the atmospheric conditions that cause atmospheric rivers and an El Niño’s capacity to bust the drought. Since March, rising sea surface temperatures in the central equatorial Pacific have indicated the formation of El Niño conditions. El Niño conditions are often associated with higher rainfall to the western United States, but it’s not guaranteed.

Savtchenko and his colleagues show that El Niño contributes only six percent to California’s precipitation variability and is one factor among other, more random effects that influence how much rainfall the state receives. While it’s more likely El Niño increases precipitation in California, it’s still possible it will have no, or even a drying, effect.

A strong El Niño that lasts through the rainy months, from November to March, is more likely to increase the amount of rain that reaches California, and Savtchenko noted the current El Niño is quickly strengthening.

The National Oceanic and Atmospheric Administration (NOAA), which monitors El Niño events, ranks it as the third strongest in the past 65 years for May and June. Still, it will likely take several years of higher than normal rain and snowfall to recover from the current drought.

“If this El Niño holds through winter, California’s chances to recoup some of the precipitation increase. Unfortunately, so do the chances of floods and landslides,” Savtchenko said. “Most likely the effects would be felt in late 2015-2016.”



56 thoughts on “California ‘rain debt’ equal to average full year of precipitation

  1. How can this study be trusted? It sees to be based on observations; no mention of models at all.

    • Good point…. :-) But a model isn’t worth as much as empiric data…. someone must forgotten they thought otherwise…. not so long ago…

      • ” … combined observations and model data …. ”
        So yes it can be trusted.
        Sarc off necessary?

    • What about this quote: “Drought has happened here before. It will happen again, and some research groups have presented evidence it will happen more frequently as the planet warms”.

      Of course, to me that felt like they had to say somewhere that humans are causing more bad weather or else their statement won’t be published.

      • Let’s just ignore California’s long and well documented history of multi-decade droughts so we can claim that it supports our pre-ordained hypothesis.

    • I think this is an excellent study and is reaffirmation of earlier studies showing most of the extreme rainfall is caused my atmospheric rivers modulated by ENSO affects on the guiding pressure systems. The The Trenberth/global warming meme that extreme rainfall is caused by global warming holding moisture fails to explain western North America’s (and elsewhere) rain fall patterns. Sometime its extreme rains and sometimes its droughts, so its not about more moisture, its how how moisture is delivered. I wrote about this regards California droughts and floods 3 years ago.

      • I agree, although I think the concept of “precipitation deficit” should be applied tenuously. It’s meaningful for reservoir and aquifer levels, but for natural ecosystems it’s all about what have you (precipitation) done for me lately.

      • Yes, and will they consider the debt repaid if an extra 20″ comes as surplus over the coming years?

  2. Amid the causes for the water shortage, no mention of the huge amount ‘set aside’ for the ….ummm… ‘all-important’ Delta Smelt, the water thus runs to the ocean, untouchable and unusable, per Federal decree.

  3. If these droughts are a regular phenomenon in California (as demonstrated by the study itself), what this “deficit” is related to? Rainy periods are taken as reference level?

    • Good point, Alexander. If the regular dry periods are the reference level, then California is generally normal with periodic rain surpluses. After the rains, it’s all back to normal.

  4. Back in January 2015, the drought warming folks claimed that California needed 13 TRILLION gallons of water to break even. Entirely coincidentally, the January 2015 “Pineapple Express” storms dropped, claimed the Weather Channel, an “atmospheric river” if 12 TRILLION gallons of water onto the state of California in only 5 days.

    Granted; a lot of the rain fell near the coast; there were floods in Marin County, for example, and we got something like 5 inches here in Sacramento. (It filled my 3 110-gallon rain barrels in an hour, and then kept raining!) Only a fraction of that made it into the foothills, and the only dams and reservoirs are …. where? … In the foothills, of course. So most of that 12trillion gallons ran down the rivers and into the Pacific.

    Perhaps we need to prepare for the next big “atmospheric river” by constructing some dams and reservoirs in Marin County, and in the coastal range. Catch the water in San Luis Obispo, and the vineyards of Paso Robles won’t have to truck the water in from very far away.

  5. And of course, our Sacramento politicians have done precisely NOTHING AT ALL to prepare more water storage facilities for the “strong El Nino event” which will start this fall. So the next big storm will cause floods on the Cosumnes and Mokolemne Rivers, much as they did during the El Nino of 1997. And with any luck, it will wash the Delta Smelt entirely out to sea!

    • Yes many midwestern people and cities took opportunities in the drought of 2012 to dig their lakes deeper and expand the capacity to hold the rains of our recent monsoon event. Carpe Diem!

  6. Living here in Cali for 58 years, it sure seems to follow my observations.
    But until I see a “hockey stick” graph, I won’t believe it.

  7. The demand for water in California will be partly off-set by the migration of people to Texas, which is now underway. Bigwigs in Sacramento see this as a more viable solution than building water storage and dams, and are working hard to encourage it.

    • If the California’s climate was in the long term more moderate, it would have in the past developed an advanced society of kind found further south.

      Ahh.., red rain. Max, in some places it has not rained for eons, if ‘geology’ can’t explain how this structure arose naturally (wind or precipitation erosion, earthquakes, volcanism, meteorite impact, succession of high and low temperatures, or any other natural process) “houston, we have a problem”.

  8. For the greenies, the word ‘conservation’ means letting water run into the oceans.

    Five massive dams were once planned for the southern UK, so that the effects of the very occasional drought could be overcome. The greenies screamed that it was better to conserve water by letting it flow into the sea.

    Greenie logic rarely makes sense, but this is one of their best. California obviously has the same problem; the disease greeniitis rarely kills, it just impoverishes everyone for no rational reason whatsoever.

    • The Government put a stop to the sensible plans for more water storage in the SE acting under an EU directive that seeks to make water a scarce resource. The SE gets enough rain if it is stored. The water companies know that so it is not their fault. Also, the SE has seen the brunt of population growth – mainly from immigration – and yet no additional water storage capacity has been created.

      • Much of the population growth is the result of people living longer. Since 1960 average life span has increased by almost 10 years. There were 430,000 residents aged 90 and over in 2011 compared with 340,000 in 2001 and 13,000 in 1911. The top 3 regions for population growth are London, East Anglia and the East Midlands.

  9. ‘The majority of that precipitation loss is attributed to a high-pressure system in the atmosphere over the eastern Pacific Ocean that has interfered with the formation of atmospheric rivers since 2011.’

    And THAT would be the year the polar vortex began its’ decent into the NA continent. I wonder if they even noticed that?

  10. It seems like that there is another side of the water shortages in California:

    “However, the state in fact has abundant water flowing into the Delta, which is the heart of California’s irrigation structure. Water that originates in the snowpack of the Sierra Nevada Mountains runs off into the Delta, which has two pumping stations that help distribute the water throughout the state.

    But on average, due to environmental regulations as well as a lack of water storage capacity (attributable, in large part, to activist groups’ opposition to new storage projects), 70% of the water that enters the Delta is simply flushed into the ocean.”

    • There is no snow pack so the water levels in the Sacramento River are low. If you pump water out of the Delta when there is low river levels you get salt water intrusion into the Delta which impacts farm land and aquifers. To go with the other chatter on this site – the state probably has a population that is beyond the carrying capacity of the physical resources that are available irrespective of climate change.

  11. Why do they need to use model output to look back only as far as 1979? Are they not records for that period?

  12. There’s plenty of precipitation over Oregon &. Washington. Capture it an build pipelines, you do have the money to accomplish that much. Then use drip irrigation.

    • B.P. – Actually, very little precip over the WA – OR Cascades this year. The Seattle metro area has limited storage capacity and water managers already very nervous about a dry 2015-2016 water year. As for the Columbia River, international and multi-state compacts govern that. Zero chance of sending any to California.

      • Last year Seattle had 30% more precipitation than average, in the first half of this year 15% less. Average itself is pretty high (952 mm/annum). If water managers are already getting nervous, it means storage capacity is limited indeed. Not only that, but they also fail to capture ongoing runoff, polluting the ocean with an excessive acidic freshwater input, while letting a precious resource go into waste.

        Now, precipitation is God’s doing, but proper water management is our own responsibility. No high population density and vigorous economic activity could be maintained for long in any area ever with large spatio-temporal variations in precipitation without heavy investments into infrastructure. But it always payed off handsomely.

        You only have to put a proper price tag on water, not a particularly high one, but a proper one. At the same time you need a legal framework which makes building an interconnected storage network easy. That’s all, the rest is a job for private enterprise.

        Geography of the west coast is somewhat unfortunate, with high mountain ranges going parallel to the coastline, capturing a cupious amount of precipitation on average and casting a huge rain shadow to the interior. However, you do not need desalination, involving costs that would really hurt, just storage and redistribution, done by a water market. For example, due to their intermittent nature, wind and solar PV are good for nothing, but pumping water. Why don’t you do that?

        Building infrastructure needs time, and no amount of money can make it go faster. Therefore it can’t offer a remedy to the current crisis, but would help with subsequent ones.

  13. We have been in a La Niña-dominant mode since 2007. There was a moderate El Niño in 2009-10 and now a new stronger one but since 2007, it has been La Niña or neutral conditions other than these.

    California’s rainfall is highly correlated to the ENSO, lagging behind by 2 to 3 months, like most atmospheric processes. It is not surprising that there is drought as a result. The rain will start returning soon based on the current El Niño

    • ..and when the November / December floods and mudslides begin, will the media coverage say “Drought Broken by Predictable Weather Pattern!” or “Global Warming Causes Extreme Weather!” ?

  14. good for a laugh-

    WMO 2014 report-

    “Global average precipitation in 2014 was close to the long-term average of 1033 mm” – 1960- 1990.

    they go onto say-

    ”The record-breaking temperatures, extreme precipitation and floods we witnessed in 2014 are consistent with what we expect from a warming climate

    so extreme precipitation is actually long term average precipitation.

    good to know that extreme, average precipitation has been helping green the world for the last 30 years oh and some extra co2.

  15. The entire southwest United States is a desert, right up to the edge of the ocean. Why is it surprising to ANYONE that California lacks rainfall? And why in the HELL do farmers insist on planting in the middle of the hottest, driest part of the North American continent and taking up 80 percent of the water piped into the state? Stupidity and near-sightedness rules again, just like the entire AGW argument.

  16. “Drought has happened here before. It will happen again, and some research groups have presented evidence it will happen more frequently as the planet warms,”

    Presented evidence? Another off-the-cuff statement served up as fact. I’m aware of several attempts to theorize a tie in between drought and a warming climate but they were all shot down quickly. Besides, it hasn’t warmed even to historical levels in the past 20 years and the CA drought is 4 years old? How does that correlate?

  17. When you look at statewide data 2013 stands out as the actual drought year, the others left CA a little dry but not in a drought 2012 was normal and 2014 was only ~14% below normal

    Plus this year – which looks only slightly dry so far.

    IMO even if CA suddenly received this “deficit” over the next 6 months they will quickly go right back to having a water shortage because their problem is not a lack a rainfall but a lack of man made water storage capacity.

  18. It looks like the last week or so Southern. Ca has been getting rain. (Warnings for flash floods etc,) Has any of this water been collected for future use? What are some of the rainfall totals for the last week and a half?

    • “Has any of this water been collected for future use?”

      According to this site:

      California has about 1300 Reservoirs. Most decently sized creeks and rivers have at lease one and in many cases multiple reservoirs. Odds are that some or the rain that fell in southern California is now in reservoirs.

      The problem is that most of the rain this year is in highly localized areas. Northern California got a lot of rain early this year. Then southern California got some. However the portion of the state that is the driest, central California, has gotten almost nothing. Yes we have Canals there to move water. However these canals were built to move water to south were it is typically the driest. We don’t have the pumping plants and canals needed to move water north from southern California, So rain in southern California doesn’t help most of the state.

  19. For crying out loud. Who paid for this? Do they know what “average” means????? Apparently, from the tone of the tome, they think their state needs to have an average amount of rain each and every year the damn thing has been in existence as a piece of land. I could have saved them a lot of money by emailing this simple little tidbit about climate: When the inner Eastern states are a hot dry brown dust bowl, Calilala Land is green. When Calilala Land is a hot dry brown dust bowl, the inner states are green.


    • Which goes a long way explaining why, at 9″, the entire state empties, screaming into bordering states, “Save me! Save me!”, then go back when rain returns, only to empty the state again with 36″ of rain, screaming into bordering states, “Save me! Save me!”.

      I really want to put a fence around that state to keep the screaming nuts confined.

  20. Since the warmists believe the CO2 is causing an almost non-existent warming, perhaps it is just as plausible that all of the wind turbines lined up along the California coast are blocking the air currents that normally carry the moisture inland. Sounds like a headline to me.

Comments are closed.