Climate Change Multimodel mean summer PDSI and standardized soil moisture over North America, 2050–2099 (

Published on March 2nd, 2015 | by Sandy Dechert


Strong Link Between California Drought & Climate Change Revealed Today

March 2nd, 2015 by  

Rain and snow have graced the West recently, causing many residents to breathe a sigh of relief about possible easing of the severe drought conditions that have worsened there over the past three-plus years. Complacency about drought and climate change is not warranted, say Dr. Noah Diffenbaugh and his research team from Stanford.

In “Anthropogenic warming has increased drought risk in California,” an article just published online today by the Proceedings of the National Academy of Sciences, Diffenbaugh and colleagues reveal proof of a somewhat counterintuitive hypothesis: higher temperatures, not necessarily precipitation shortages, drive the phenomenon of drought.

Diffenbaugh heads the Climate and Earth System Dynamics research group in the School of Earth, Energy & Environmental Sciences at Stanford, where he’s an associate professor and a senior fellow in the Stanford Woods Institute for the Environment. He was behind last September’s conclusions that climate change is occurring 10 times faster now than at any time in the past 65 million years. He has also said that at its current pace, climate change will involve a 5- to 6-degree Celsius rise by 2100.

About the current study of drought and climate change, Diffenbaugh notes:

“Of course low precipitation is a prerequisite for drought, but less rain and snowfall alone don’t ensure a drought will happen. It really matters if the lack of precipitation happens during a warm or cool year. We’ve seen the effects of record heat on snow and soil moisture this year in California, and we know from this new research that climate change is increasing the probability of those warm and dry conditions occurring together.”

The concept of long-term megadrought has startled many over the past couple of weeks. Benjamin Cook of NASA’s Goddard Institute and Ocean and Climate Physics at Columbia’s Lamont-Doherty Earth Observatory, with colleagues Jason Smerdon, also of Columbia, and Toby Ault from Earth and Atmospheric Sciences at Cornell, introduced the term while examining historical episodes of drought in the Central Plains and Southwest.

Multimodel mean summer PDSI and standardized soil moisture over North America, 2050–2099 (

Through soil moisture indicators and 17 different climate models, Cook’s team concluded that the risk of severe and protracted droughts in these regions is rising to unprecedented levels. Readings like these have not been seen since the Medieval Climate Anomaly 1,000 years ago, when a 50-year drought and successive water shortages forced the ancient Pueblo people to abandon their sprawling metropolis and once-thriving trade center at Chaco Canyon.

Chaco Canyon, New Mexico, Ancient Peoples Pueblo (

Peter Gleick, hydroclimatologist co-founder and head of the Pacific Institute in Oakland, California, told Slate magazine in a recent story about the Cook et al. work, “We cannot hope that losses in the Southwest will be made up in the Midwest, according to this study.” Pointing to demographic trends toward population increases, Gleick casually concluded, “There are degrees of screwed, and this paper suggests we’re falling off the cliff.”

The research PNAS released today offers other important points about the megadrought phenomenon and strengthens its climate change links. Like the other research group, Diffenbaugh addresses the growing risk of drought expansion in the US West, but this time from the focus of 120 years of recently released California monthly precipitation, temperature, and drought and climate change statistics.

His team’s analysis reveals that warm and dry years, characterized by increased snowmelt, higher water loss from plants and soils, and diminished water availability, have been about twice as likely recently to produce severe drought as years that were also dry, but cooler. The current California drought is one of the longest stretches in the 120-year historical record during which conditions have been both severely dry and severely warm. Says Dr. Diffenbaugh:

“Our findings… provide very strong evidence that global warming is already making it much more likely that California experiences conditions that are similar to what we have experienced during the current severe drought.”

With Peter Gleick, Michael Mann, the climatologist and geophysicist famous for the “hockey stick” climate graph who currently directs of the Earth System Science Center at Pennsylvania State University, has reviewed today’s new drought and climate change study for PNAS. Mann says:

“Diffenbaugh et al. now add weight to the accumulating evidence that anthropogenic climatic changes are already influencing the frequency, magnitude, and duration of drought in California.”

Gleick, who developed the first analysis of climate change impacts on water resources, drew up a telling plot at the new year of California temperature and precipitation anomalies over the full instrument record from 1895 through November 2014. His figure, which will be updated for the PNAS review, shows that the three-year period ending in 2014 was by far California’s hottest and driest on record. Note the extreme position of that data point.

Recorded California temperature and precipitation  anomalies (Gleick, 12/31/14 from twitter)

The new set of measurements from Diffenbaugh and colleagues should allow scientists to quantify better how much drought Californians have undergone, how much they can anticipate for the future, and how it will affect agricultural production, under different climate change scenarios. These findings should help California farmers, water managers, and state officials make more realistic plans for using the resource and better regulate the recently substantial drawdowns of groundwater.

On a final and slightly more positive note, drought and climate change scenarios vary. We don’t necessarily have to limit ourselves to the worst case. Moving along quickly with deep decarbonization, mitigation, and adaptation may leave more than a drop in California’s dwindling reservoirs and now-threatened aquifers.

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About the Author

covers environmental, health, renewable and conventional energy, and climate change news. She's currently on the climate beat for Important Media, having attended last year's COP20 in Lima Peru. Sandy has also worked for groundbreaking environmental consultants and a Fortune 100 health care firm. She writes for several weblogs and attributes her modest success to an "indelible habit of poking around to satisfy my own curiosity."

  • Hazel

    Wikipedia has a good article on coal, which indicates the hydrogen content of various grades, it varies quite widely. Multiply that by about 9, and you get the amount of water coming out of coal. So for 5% hydrogen 75% carbon, which seems about the average, that would have (75*44÷12) ÷ (5*18÷2) = 6.1 times as much CO₂ as water emissions. In contrast, natural gas is somewhat over 75% carbon 25% hydrogen by mass (that’s the methane ratio, other hydrocarbons are higher), so about 1.2 times as much CO₂ as water.

    That said, water content of the atmosphere is pretty much constant, and there have been huge net transfers from surface and aquifers to oceans over the past couple hundred years, mainly due to human agricultural activity. This was responsible for something like 40% of the 20th century sea level rise (according to a PNAS paper around 2011, I can get the source if you like). Things like the Aral and Caspian seas drying up, along with North American and other aquifers.

    Net result: any water resulting from hydrocarbon combustion is going up the stack and then ending up in the oceans, contributing to sea level rise. But it’s not much, and it’s probably smaller in (short-term) economic/human impact than the loss of surface and aquifer fresh water used for cooling combustion power plants.

    • VooDude

      Ultimately, all water ends up in the ocean. It is the flow of water from land, into the ocean, that provides land organisms with fresh water. Most fossil fuel combustion occurs over land, and land is 30% of the surface of the earth. From this, I would assume that more than 30% of the “new water” created by fossil fuel combustion is initially deposited on land, and in particular, near where the fossil fuel was combusted (which, in turn, is near human population centres). However small this “new water” is, the flow of “new water” benefits the places where surface and aquifer water are being used by Mannkind. In the same fashion, surface water pumped to cool combustion power plants is also recycled, at least 30% on land, and probably near the power plant itself.

      I am unaware of any water pumped from freshwater aquifers that is lost to cooling combustion power plants. Please enlighten us with a few examples.

      Modern, combined-cycle natural gas power plants exceed the Carnot limitation of efficiency, and approach 80% efficiency. Modern solar cells convert shortwave sunlight into electricity, but at less than 20% efficiency. Solar cells are not usually water-cooled, so the majority of the left-over 80% of sunshine gets converted to localized heat of the air. Kilowatt-hour compared to kilowatt-hour, electric generation from combustion, or solar, creates heat. Heat causes evaporation … Kwh for Kwh, is there any difference in solar, versus combustion, in the ultimate hydrological cycle?

  • Ifrah Khan @GreenGlobalTravel

    Great article about reasons behind climate change. Ifrah Khan@GreenGlobalTravel

  • Hazel

    Good article, it shows clearly that heat and drought are linked.

    Fortunately, wind and solar not only reduce global warming pollution, they also reduce or eliminate water consumption by the electricity sector. Amazingly, nationwide over half of the fresh surface water is consumed by electric power generation, see image below and:

    This point is rarely part of the renewable energy conversation, but is particularly relevant to the southwest.

    • VooDude

      For every kilogram of fossil fuel burned, CO2 is released, but about a kg of new water is created (well, “liberated”)

      • Hazel

        I have to take issue with your wording. Water isn’t “liberated” from the fossil fuel, it’s created by pulling oxygen out of the atmosphere to combine it with the hydrogen in the fuel. That is, unless you’re burning hydrated methane, in which case you’re wasting a lot of energy. And this doesn’t apply at all to coal of course.

        Furthermore, the diagram here is about fresh water available for things like drinking, agriculture, and other industrial and commercial purposes. Putting a few more drops of water into the atmosphere really doesn’t help with that. Reducing its use in the first place by substituting solar and wind helps a lot.

  • Larry

    I see a couple of flat earthers are already posting. This headline shouldn’t be subject to question. The data clearly shows the new trend lines and anyone who is willing to look at the data with an open mind will arrive at the same conclusion. Constant dumping of excess heat energy into the earth’s atmosphere by combustion of mega amounts of fossil fuels is now overloading the system. Natural buffers have been overloaded and the results are hotter temperatures and major changes in precipitation patterns. This is now the new “average” and the results are foreboding.

    • Omega Centauri

      Its not the dumping of heat of combustion, which is tiny compared to the overall solar energy driving the system. Its the change in the atmospheric infrared transparency, which means more heat that would have escaped to space, gets absorbed and rerediated back towards the gound. The greenhouse effect is orders of magnitude more important than the direct heating.

  • Ago Solvo

    I call bullshit. “Scientists studying long-ago California climate have realized that the 20th century was abnormally wet and rainy, according to researcher Lynn Ingram, professor in the Department of Earth and Planetary Science at UC Berkeley.“The past 150 years have been wetter than the past 2,000 years,” Ingram said. “And this is when our water development, population growth and agricultural industry were established.”

    • rockyredneck

      The article claims it is equivalent of the medieval warm period 1000 years ago. In other words (normal over periods of a few thousand years).

    • VooDude

      NOAA released these statements: ”The [2011-2014] 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.”


      ”The current drought, though extreme, is not outside the range of California hydro-climate variability and similar events have occurred before. Although there has been a drying trend in California since the late 1970s, when considering the full observational record since 1895, there is no appreciable trend to either wetter or drier California winters.”

      ”Determining human-induced climate change from the observational record is difficult. Across North America there is strong interannual to decadal and multidecadal variability of precipitation which means that observed trends, even over very long time periods, could arise from natural variability.”

      ”The CMIP5 models project that rising greenhouse gases should increase California winter precipitation, but that changes, to date, are small compared to the recent drought anomalies. As such, the recent drought was dominated by natural variability, a conclusion framed by a discussion of the differences between observed and modeled tropical SST trends over the past decades.”

      ”…models found no substantial effect of human-induced climate change on the severe precipitation deficits over California (Herring et al. 2014).”


      • Leslie Graham

        As you almostly certainly are aware that report refers to average rainfall and does not include the increased evaporation rates caused by record high temperatures.
        Soil moisture deficits were at record highs by a huge off-the-charts margin in 2014.
        Even if rainfall levels continued to remain at constant levels – which just about every other study I’ve read says they won’t – then soil moisture deficits will continue to increase long term.
        Nice try though. You probably managed to confuse a few lay people which was your aim really wasn’t it?

        • VooDude

          ” report refers to average rainfall and does not include the increased evaporation rates caused by record high temperatures … Soil moisture deficits were at record highs”
          Apparently, your dispute is with NOAA. “Soil Moisture” readings don’t go back very far in time, so “record highs” is not a good qualifier.
          Paleo proxy records for drought show, that for all recorded history, California has been in a pluvial period; an unusually wet one, at that: since about 1500 AD

          When you talk about California’s drought history, you should include the Stein periods:

          The drought in California is bad, but apparently it has been worse… Fallen Leaf lake, in the Sierra Nevada (among other sites) has been discovered to have old trees rooted in soil that is now seventy feet below lake level. That means that the lake had to be more than 70′ lower, because those trees don’t root in water or wet soil. Those old trees had lived there for 200 years.

          Modern experiences of the climate in California, spanning only the last several hundred years, appear to have been during an unusually wet period. A drought that was drier, and lasted longer, spanning the period of AD 1085-1153, is indicated by tree studies conducted in the Sierra Nevada area around Lake Tahoe. Evidence such as this is usually “attributed to extended periods of very dry conditions during the mid and late Holocene, with the most recent mega-droughts happening during Medieval times…”(1) This drought appears to have started about 900 years ago, and apparently lasted 220 years or more. Pine trees don’t root underwater, nor do they survive with their roots submerged for long. Tree remains, apparently still rooted to the soil, were found in Fallen Leaf Lake, more than 100 feet below the present day lake level. Radiocarbon dating and dendrochronological studies provide the dating. This suggests that, some 900 years ago, that soil was dry enough for pine trees to root and grow, reaching a circumference greater than 4m and a height of over 30m. One branch was found to have about 200 rings; One trunk cross-section, 220 rings.


          The Colorado River, and the Green River, as they flow through Utah, show an up-tic in stream-flow at about 1900 onwards, again indicating that what we perceive as “California recorded history” (which doesn’t stretch back very far) is an unusually wet period.


          “Tree-ring data from the [Upper Colorado River Basin] indicate that even more severe droughts have occurred in the past, and that the current drought is the seventh worst, in an approximately 500-year proxy record. The largest drought in the tree ring data occurred at the end of the sixteenth century and lasted for at least 20 years …”(3)


          “The two most severe, sustained droughts in the continental United States during the 20th century occurred in the 1930s and 1950s.” “The Dust Bowl … was the nations most severe, sustained, and widespread drought of the past 300 years, according to tree-ring reconstructions of the Palmer drought severity index (PDSI) across the continental United States …” (3)

          1: Biondi, Franco, J. Kleppe, and Scotty Strachan 2006. “Underwater dendrochronology of Sierra Nevada Lakes.” workshop on science as a tool in Lake Tahoe Basin Management, Incline Village, Nevada

          2:Piechota, Thomas, et al. 2004 “The western US drought: How bad is it?” Eos, Transactions American Geophysical Union

          3: Stahle, David W., et al. 2000 “Tree‐ring data document 16th century megadrought over North America.” Eos, Transactions American Geophysical Union

        • VooDude

          This comment was a dupe, so I edited it out.

  • dxing

    Scientist at Lawrence Berkeley Lab have for the first time been able to
    measure Global warming AKA C02 Climate Forcings directly using actual
    Lab instruments, in this case spectrometers measuring the actual C02 radiation signature;
    youtube : CO2 Surface Forcing Time Series

  • Joseph Dubeau

    Good article Sandy,

    For anybody whom may be interested.
    Study Links Syria Conflict to Drought Caused by Climate Change

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