Key facts about the drought that’s reshaping California.

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

“We don’t even plan for the past.”
— Steven Mosher (member of Berkeley Earth; bio here), a comment posted at Climate Etc.

Contents

1. The California drought: it’s bad.
2. Climate Science gives us worse news.
3. About our water stocks.
4. Causes of these droughts.
5. California’s mad water use.
6. Useful Sources of Information.
7. For More Information.
8. 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.

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 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 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.

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.

(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. 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:

• “Lack of Snow Leaves California’s ‘Water Tower’ Running Low“, National Geographic, 4 March 2015 — “Rising temperatures and declining snowpack in the mountains mean that the drought across the western U.S. is about to get even worse.”
• “California Farmers Confront Ominous Groundwater Shortage“, Scientific American, 6 March 2015 — “Drought and saltier aquifers pose threats to the biggest farming state in the U.S. “
• “California has about one year of water left. Will you ration now?“, Jay Famiglietti (senior water scientist at NASA JPL, prof of Earth system science at UC Irvine), op-ed in the LAT, 12 March 2015.

(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).

Most journalists have written good articles about this research. See “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.”  Also see “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.” Now for the research (red emphasis added to the good 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.

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 their 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)  “Recent California Water Year Precipitation Deficits: A 440-year Perspective“, Henry F. Diaz and Eugene R. Wahl, Journal of Climate, in press — Abstract:

An analysis of the October 2013–September 2014 precipitation in the western United States and in particular over the California-Nevada region suggests this anomalously dry season, while extreme, is not unprecedented in comparison with the ~120-year long instrumental record of water year (WY: October–September) totals, and in comparison with a 407-year WY precipitation reconstruction back to 1571. Over this longer period nine other years are known or estimated to have been nearly as dry or drier than WY 2014.

The 3-year deficit for WY’s 2012–2014, which in the California-Nevada region exceeded the annual mean precipitation, is more extreme but also not unprecedented, occurring three other times over the past ~ 440 years in the reconstruction. WY precipitation has also been deficient on average for the past 14 years, and such a run of predominantly dry WY’s is also a rare occurrence in our merged reconstructed plus instrumental period record.

(4)  Causes of the drought

Journalists have mostly covered this well, as in these two stories from the New York Times:  “Science linking drought to global warming in dispute“ (16 February 2014) and “A climate analyst clarifies the science behind California’s extreme drought” (6 March 2014). Also see this from Mashable: “California Drought Is Worst Since at Least 1895, Data Shows” (14 August 2014).

Unfortunately, climate models are not yet able to give reliable forecasts for regional precipitation (they do neither well). Here is research about the causes of the drought (will be updated with new research).

(a)  “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.”

(b)  “A link between the hiatus in global warming and North American drought“, Thomas L. Delworth et al, Journal of Climate, May 2015 — 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. Climate models and observational analyses are used to clarify the dual role of recent tropical Pacific changes in driving both the global warming hiatus and North American drought.

When observed tropical Pacific wind stress anomalies are inserted into coupled models, the simulations produce persistent negative sea surface temperature anomalies in the eastern tropical Pacific, a hiatus in global warming, and drought over North America driven by SST-induced atmospheric circulation anomalies. In the simulations herein the tropical wind anomalies account for 92% of the simulated North American drought during the recent decade, with 8% from anthropogenic radiative forcing changes.

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.

The model experiments suggest that if the tropical winds were to return to climatological conditions, then the recent tendency toward North American drought would diminish. Alternatively, if the anomalous tropical winds were to persist, then the impact on North American drought would continue; however, the impact of the enhanced Pacific easterlies on global temperature diminishes after a decade or two due to a surface reemergence of warmer water that was initially subducted into the ocean interior.

(c)  From NOAA: “Causes and predictability of the 2011 – 2014 California Drought“, December 2014 — Excerpt (emphasis added):

The current drought is not part of a long-term change in California precipitation, which exhibits no appreciable trend since 1895. Key oceanic features that caused precipitation inhibiting atmospheric ridging off the West Coast during 2011-14 were symptomatic of natural internal atmosphere-ocean variability.

Model simulations indicate that human-induced climate change increases California precipitation in mid-winter, with a low-pressure circulation anomaly over the North Pacific, opposite to conditions of the last 3 winters. The same model simulations indicate a decrease in spring precipitation over California. However, precipitation deficits observed during the past three years are an order of magnitude greater than the model simulated changes related to human-induced forcing. Nonetheless, record setting high temperature that accompanied this recent drought was likely made more extreme due to human-induced global warming.

(d)  “Causes of the 2011 to 2014 California drought“, Richard Seager et al, Journal of Climate, in press — Ungated version. Abstract (emphasis added):

The causes of the California drought during November to April winters of 2011/12 to 2013/14 are analyzed using observations and ensemble simulations with seven atmosphere models forced by observed SSTs. Historically, dry California winters are most commonly associated with a ridge off the west coast but no obvious SST forcing. Wet winters are most commonly associated with a trough off the west coast and an El Niño event.

These attributes of dry and wet winters are captured by many of the 7 models. According to the models, SST forcing can explain up to a third of California winter precipitation variance. SST-forcing was key to sustaining a high pressure ridge over the west coast and suppressing precipitation during the three winters. In 2011/12 this was a response to a La Niña event whereas in 2012/13 and 2013/14 it appears related to a warm west, cool east tropical Pacific SST pattern. All models contain a mode of variability linking such tropical Pacific SST anomalies to a wave train with a ridge off the North American west coast. This mode explains less variance than ENSO and Pacific decadal variability and its importance in 2012/13 and 2013/14 was unusual.

The CMIP5 models project rising greenhouse gases to cause changes in California all-winter precipitation that are very small compared to recent drought anomalies. However, a long term warming trend likely contributed to surface moisture deficits during the drought. As such, the precipitation deficit during the drought was dominated by natural variability, a conclusion framed by discussion of differences between observed and modeled tropical SST trends.

(e)  “Causes of the 2011–14 California Drought“, Richard Seager et al, Journal of Climate, September 2015. Abstract only.

The causes of the California drought during November–April winters of 2011/12–2013/14 are analyzed using observations and ensemble simulations with seven atmosphere models forced by observed SSTs.

… The models from phase 5 of CMIP (CMIP5) project rising greenhouse gases to cause changes in California all-winter precipitation that are very small compared to recent drought anomalies. However, a long-term warming trend likely contributed to surface moisture deficits during the drought. As such, the precipitation deficit during the drought was dominated by natural variability, a conclusion framed by discussion of differences between observed and modeled tropical SST trends.

(f)  “How Has Human-induced Climate Change Affected California Drought Risk?“, Linyin Cheng et al, Journal of Climate, in press. Gated; open copy at ReserachGate. Abstract:

… How has human-induced climate change affected California drought risk? Here, observations and model experimentation are applied to characterize this drought employing metrics that synthesize drought duration, cumulative precipitation deficit, and soil moisture depletion. The model simulations show that increases in radiative forcing since the late 19th Century induces both increased annual precipitation and increased surface temperature over California, consistent with prior model studies and with observed long-term change. As a result, there is no material difference in the frequency of droughts defined using bivariate indicators of precipitation and near-surface (10-cm) soil moisture,

… The results thus indicate the net effect of climate change has made agricultural drought less likely, and that the current severe impacts of drought on California’s agriculture has not been substantially caused by long-term climate changes.

(g)  “Old World megadroughts and pluvials during the Common Era“, Edward R. Cook, et al, Science Advances, 6 Nov 2015 — See the press release. Excerpt…

In addition, megadroughts reconstructed over north-central Europe in the 11th and mid-15th centuries reinforce other evidence from North America and Asia that droughts were more severe, extensive, and prolonged over Northern Hemisphere land areas before the 20th century, with an inadequate understanding of their causes.

… By comparison, the worst megadrought in the California and Nevada regions of the NADA (26) lasted from 832 to 1074 CE …

(h)  “Is there a role for human-induced climate change in the precipitation decline that drove the California drought?” by Richard Seager et al. in the Journal of Climate, in press. Conclusion of the abstract…

These results allow a tenuous case for human-driven climate change driving increased gradients and favoring the west coast ridge but observational data are not sufficiently accurate to confirm or reject this case.

(5)  California’s mad water use policies.

Key fact: Agriculture & related manufacturing use ~4/5’s of California’s water use, but produce only 2% of its GDP and 4% of its jobs. (Public Policy Institute of California).

This crisis didn’t just happen. We were warned, and must make large-scale public policy changes. California has much water; a rational farming program could still produce larger crops. For more about our mad water policies:

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. “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?”
3. “California faces growing water management Challenges“, Public Policy Institute of California, January 2014.
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 drying of the West“, The Economist, 22 February 2014 — “Drought is forcing westerners to consider wasting less water.”
6. “California’s Almonds Suck as Much Water Annually as Los Angeles Uses in Three Years“. Mother Jones, 12 January 2015.

(6)  Useful Sources of Information

The Internet provides a wealth of information about climate. NOAA especially provides wonderful tools to understand these issues.

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”.

Update: “California’s Snowpack Is Now Zero Percent of Normal” by Eric Holthaus at Slate. Good data. It’s Slate so concludes with unjustified alarmism: “Welcome to climate change, everyone.”

(7)  For More Information

See the 1993 classic book forecasting our present problems Cadillac Desert: The American West and Its Disappearing Water. If you liked this post, like us on Facebook and follow us on Twitter. Also, see these other posts about droughts:

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?

(8)  The Hydro-Illogical Cycle

From the SPEI website.