The Key Facts about California’s Drought, Except When It will End

March 16th, 2015
in econ_news

by Fabius Maximus,

Summary: California's drought might be to us what the dust bowl of the prairies was to the 1930s (irony: California was the big beneficiary of that drought). This post answers most of your questions about the drought, cutting through the media chaff of misinformation (but does not discuss its effects). This is an update of a November post. {1st of 2 posts today.}

"We don't even plan for the past." - Steven Mosher (member of Berkeley Earth; bio here), a comment posted at Climate Etc.

Follow up:

Preparing for Extreme Weather
From the NCAR-Wyoming Supercomputing Center


  1. The California drought: it's bad
  2. Climate Science gives us worse news
  3. About our water stocks
  4. Articles about this & past California droughts
  5. Useful Sources of Information
  6. For More Information
  7. The Hydro-Illogical Cycle

(1) The California drought: it's bad.

It's bad, with no end in sight. We get most of our water from the winter rain, which has been below- average so far (85% of average; rank 57 of the past 120 years; the past 12 months numbers are similar). Not what we need to refill the reservoirs. See the story in pictures below; click all images to expand.

Precipitation this winter in California
From the California Climate Tracker website. Click to expand.

How bad is it? Let's look at the past year (the California "water year" runs from October to September). The average is 23″; 1924 was the driest year at 9″; 6 of past 8 years were dry. The previous "water year" (ended Oct 2014) was 12″ (3rd driest in the past 119). Jan and Feb were especially bad this year.

It can get worse, much worse. The 1917 - 1934 drought ran 17 years with only one year of above-average rainfall (including the record low year of 1924)!

Precipitation is just one factor that makes a drought. Temperature also has a large effect on the soil. Hence the creation of sophisticated indexes to measure droughts, such as the Palmer Drought Severity Index and the Standardised Precipitation-Evapotranspiration Index (SPEI).

Rainfall in California has been low, but not unusually so (as climate goes). But it's warm, and so the drought indexes for California are at their lows for the past century. Sixty percent of the West is in moderate to exceptional drought (also see this graph), although not as bad as California's.

Some misunderstand the situation, as in this article at Watts Up with That. The article opens with a map of the Palmer Index for California, and then ignores it - concluding that the experts cited in the above articles are wrong, and describing this as the worst California drought on record is a "wildly incorrect statement that seems focused on creating public panic." Not so.

Graph of SPEI California
From Mashable, 14 August 2014. Click to expand.

Now for the very bad news. This year has been bad, but drought's impact increases over time. And this drought is in its 4th year. See the 48 month SPEI back to 1895, with NOAA's comment:

{California} has a rank of driest {in its recorded history} for the last 24, 36, and 48 months; second driest for the last 60 months (behind 1986-1991); and third driest for the last 72 months.

Long-term graph of SPEI index for California
From NOAA website, 11 March 2015. Click to expand.

(2) About our water stocks

California's reservoirs are at 46% of average on February 28 (this includes Lake Powell and Lake Mead). See this graphic version.

How about the snowpack? As of March 3:

Statewide, 103 electronic sensors found today's snow water equivalent to be 5 inches, 19% of the March 3 multi-decade average. ... The snowpack's water content this year is historically low for early March. Only in 1991 was the water content of the snowpack lower - 18% of that early-March average. Manual surveys of 180 snow courses this year reveal even less water content - just 13% of the early - March average, the lowest in DWR's records for this time of year.

... In normal years, the snowpack supplies about 30 percent of California's water needs as it melts in the spring and early summer.

Groundwater levels have been dropping fast. See this graph of the drop during the past 10 years ending Spring 2014. Note how much of the Central Valley has had drops of ten feet or more. See more data here.

For more about this:

(3) Climate science research gives us worse news.

As usual here, here we let scientists speak for themselves. The following articles provide an antidote to the confident assertions of climate activists that blame all extreme weather on climate change, such as "The Crisis Over California's Water" by Joshua Frank at Counterpunch (citing 2 scientists' theory does not make it fact, especially for historically common phenomena; also note the implication that all climate change is anthropogenic). Red emphasis added to the interesting parts.

(a) "Long-Term Aridity Changes in the Western United States", Edward R. Cook et al, Science, 5 November 2004 - A mildly stated conclusion:

If the Z-C modeling results hold up, it is plausible that continued warming over the tropical Pacific, whether natural or anthropogenically forced, will promote the development of persistent drought-inducing La Nina-like conditions. Should this situation occur, especially in tandem with midcontinental drying over North America, the epoch of unprecedented aridity revealed in the DAI reconstruction might truly be a harbinger of things to come in the West.

History of drought in western USA
Cook et al, Science, 5 November 2004. Click to expand.

The Colorado River Compact, allocating the water, was negotiated in 1921 - near the wettest time during the past 1,200 years.

(b) "North American drought: Reconstructions, causes, and consequences", Edward R. Cook et al, Earth-Science Reviews, March 2007 - In this later paper, Cook et al give us the long-suspected bitter news. Excerpt from "conclusions":

These reconstructions, many of which cover the past 1000 years, have revealed the occurrence of a number of unprecedented megadroughts over the past millennium that clearly exceed any found in the instrumental records since about AD 1850, including an epoch of significantly elevated aridity that persisted for almost 400 years over the AD 900-1300 period. In terms of duration, these past megadroughts dwarf the famous droughts of the 20th century, such as the Dust Bowl drought of the 1930s, the southern Great Plains drought of the 1950s, and the current one in the West that began in 1999 and still lingers on as of this writing in 2005.

... The extraordinary duration of past North American megadroughts is difficult to explain, but climate models strongly point to tropical Pacific Ocean SSTs {sea surface temperatures} as a prime player in determining how much precipitation falls over large parts of North America.

(c) Unfortunately, climate models are not yet able to give reliable forecasts for regional precipitation (they do neither well): "The Key Role of Heavy Precipitation Events in Climate Model Disagreements of Future Annual Precipitation Changes in California", David W. Pierce et al, Journal of Climate, August 2013 - Open copy here.

"Climate model simulations disagree on whether future precipitation will increase or decrease over California, which has impeded efforts to anticipate and adapt to human-induced climate change. This disagreement is explored in terms of daily precipitation frequency & intensity."

(d) Working to understand the causes of the drought: "A link between the hiatus in global warming and North American drought", Thomas L. Delworth et al, Journal of Climate, in press - Abstract:

Portions of western North America have experienced prolonged drought over the last decade. This drought has occurred at the same time as the global warming hiatus - a decadal period with little increase in global mean surface temperature. We use climate models and observational analyses to clarify the dual role of recent tropical Pacific changes in driving both the global warming hiatus and North American drought.

... This suggests that anthropogenic radiative forcing is not the dominant driver of the current drought, unless the wind changes themselves are driven by anthropogenic radiative forcing. The anomalous tropical winds could also originate from coupled interactions in the tropical Pacific or from forcing outside the tropical Pacific. ...

(4) Articles about this and past California droughts.

Here are excellent explanations written for a general audience.

(a) Past droughts, an example - and warning:

  1. "California drought: Past dry periods have lasted more than 200 years, scientists say", San Jose Mercury News, 25 January 2014 - "Researchers have documented multiple droughts in California that lasted 10 or 20 years in a row during the past 1,000 years."
  2. "Could the California drought last 200 years?", National Geographic, 13 February 2014 - "Clues from the past suggest the ocean's temperature may be a driver."

(b) Water management in California

  1. "Drought in the United States: Causes and Issues for Congress", Congressional Research Service, 12 August 2012 - What do you guess Congress did with these recommendations?
  2. "California faces growing water management Challenges", Public Policy Institute of California, January 2014.
  3. "The drying of the West", The Economist, 22 February 2014 - "Drought is forcing westerners to consider wasting less water."
  4. "It Takes How Much Water to Grow an Almond?!", Mother Jones, 24 February 2014 - "Why California's drought is a disaster for your favorite fruits, vegetables, and nuts."
  5. "The Dust Bowl Returns", Blain Roberts and Ethan J. Kytle (Assoc Profs of History at CSU - Fresno), op-ed in the New York Times, 9 February 2013 - "How long can we continue to grow a third of the nation's fruit and vegetables?"

(c) Analysis of the drought

  1. "Science linking drought to global warming in dispute", New York Times, 16 February 2014 - "It all adds up across the Southwest to an increasingly stressed water system. That's what they might as well get ready for."
  2. "A climate analyst clarifies the science behind California's extreme drought", Andy Revkin, New York Times, 6 March 2014.
  3. "Clarifying the discussion about California drought and climate change", Peter Gleick (President, Pacific Institute), Science Blogs, 6 March 2014.
  4. "California Drought Is Worst Since at Least 1895, Data Shows", Mashable, 14 August 2014.

(5) Useful Sources of Information.

The Internet provides a wealth of information about climate. NOAA especially provides wonderful toys.

  1. Make your own climate map, showing precipitation or one of the drought indexes.
  2. Make your own animated climate map, showing the evolution of the drought over time.
  3. NOAA's Seasonal Drought Outlook at the Climate Prediction Center.
  4. The U.S. Drought Portal - A wealth of information about past and present droughts in USA, and their impacts.
  5. US Drought Monitor - U Nebraska - Lincoln and Federal Agencies - Ditto as above.
  6. The California Climate Tracker - make graphs and maps of California climate data. By the Desert Research Institute.
  7. Westmap - make graphs and maps of climate date. By the Desert Research Institute
  8. Paleoclimate Drought Resources - "What paleoclimatology tells us about drought, from the World Data Center for Paleoclimatology".

Truth Will Make You Free

(6) For More Information.

See these posts:

  1. Have we prepared for normal climate change and non-extreme weather?
  2. Let's prepare for past climate instead of bickering about predictions of climate change.
  3. Droughts are coming. Are we ready for the past to repeat?

(7) The Hydro-Illogical Cycle

The Hydro-illogical cycle
From the SPEI website

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