Climate Change

1.2 History of Drought in California Paints Troublesome Outlook

Jaymes T. StClair

A lack of winter precipitation in California, alongside a previously dry environment, threatens a recurrence of the 1970s drought conditions and subsequent water restrictions. What is causing the prolonged series of droughts? Do recent drought events foretell the future of water supply management in California?
Dead lawn in front of California state house
Figure 1. During drought conditions, many properties, including California’s state house in Sacramento, conserve water by foregoing non-essential practices.
Photograph by Kevin Cortopassi, 2014. CC BY-ND 2.0.

California has always had a water problem. The aqueduct system that was developed for the city of Los Angeles was a feat of spectacular engineering. However, a moderately large percentage of the water that the state uses derives from snowpack in the Sierra Nevada mountain range. Many studies have developed models that can predict winter precipitation so California is able to properly allocate water resources for the dry summer months. In a recent study, Peter Caldwell questions the reliability of two prominent precipitation models.1 These models, namely regional climate models and general circulation models, have performed poorly in predicting the amount of precipitation that California will receive.1 Results have shown that regional climate models regularly over predict precipitation totals, while conversely, most general circulation models underestimate precipitation totals.1 Local officials use precipitation models to determine how much water will need to be purchased and diverted into the many agricultural valleys of the state. There may be devastating economic and political consequences if these officials rely on unpredictable models such as regional climate models and general circulation models.

Progression of 2014 drought in California
Figure 2. Drought Conditions in California from December 2013 through July 2014.
Courtesy of National Drought Mitigation Center, 2014. Public Domain.

One location where recent droughts can be clearly witnessed is the Folsom Lake watershed, which is located near the slopes of the Sierra Nevada mountain range (Figure 3). The current reservoir level of the lake is so low that the remnant of a ghost town from the Gold Rush era is visible.2 The water districts that rely on water from Folsom Lake have urged consumers to reduce water usage by at least twenty percent. This is similar to standards implemented during the drought periods of the 1970s. A hydrologic research study done by Jianzhong Wang and Konstantine Georgakakos used simulation models to look at the sensitivities of dynamic precipitation during the winter over the Lake Folsom watershed.3 The simulation spanned thirty-five years and utilized data from sixty-two winter storms. The results suggested that precipitation prediction models were not as accurate for light and moderate precipitation levels.3 This inaccuracy is similar to the inaccuracies found in the precipitation models previously mentioned, and can lead to similar problems for local officials trying to control water consumption during dry summer season.

Folsom Lake during drought and non-drought conditions
Figure 3. Lake Folsom is one of California’s reservoirs that is heavily impacted by drought. These before and after pictures show the water levels in Folsom Lake before and during the 2012-2014 North American Drought.
Photographs by the California Department of Water Resources, 2014. Public Domain.

There are many water reservoirs around the Sierra Nevada Mountains that rely on the winter snowpack. More than 25 million people and the $44.7 billion agricultural industry of California use the water from snow that melts off the 650 kilometers (400 mile) mountain range.4 In January 2014, the snowpack was just twenty percent of the historical average.2 The visual evidence from a satellite image of this lessened snowpack is staggering (Figure 4). In a study by Kim et al., ten to thirty percent of cold season precipitation derives from atmospheric river landfalls.5 With high pressure systems diverting nearly all forms of precipitation north, droughts are exacerbated as expected precipitation is diverted away from the coast.6

Sierra Nevada snowpack in 2013 and 2014
Figure 4. Snowpack on the Sierra Nevada Mountain Range. In the southwestern United States, snowpack from the Sierra Nevada mountains is an important source of freshwater. Record low snowfall in 2014 prolonged the already severe drought.
Photographs by NASA/NOAA, 2014. Public Domain.

Studies conducted on the possible impacts of severe and sustained droughts in California are numerous because bringing water to the many valleys of the state is complex and costly. California faces the enduring challenge of high evaporation paired with low precipitation. In a historical study examining a medieval climate Glen MacDonald discovered an anomaly that consisted of prolonged episodes of arid conditions and severe droughts spanning five hundred years.7 These conditions are linked to the abandonment of the affected regions by local native tribes and to increased violence between the tribes over precious fertile lands.7 MacDonald suggests that a similar event could occur in the future due to natural or anthropogenic causes.7 MacDonald also looked at the impacts of a “perfect” drought on southern California. The “perfect” drought consists of a prolonged drought in southern California paired with simultaneous similar conditions in the Sacramento River basin and upper Colorado River basin.8 There is evidence that all these conditions occurred in the 11th and 12th centuries during this climate anomaly.8 Therefore, the scientists believe California is experiencing prolonged periods of drought caused by climate change.

California is currently undergoing a series of droughts that could possibly rival the severe droughts witnessed during the 1970s. The current drought is caused by an unprecedented high pressure ridge that is just offshore of the west coast. This high pressure ridge is blocking all of the winter storms needed to provide the necessary precipitation for the dry summer months and has been diverting weather systems to the north for the past thirteen months (as of January 2014). This is an abnormal amount of time for a system like this to remain uninterrupted. Climatologists say that the longer the system persists, the less likely approaching winter storms will be able to break through.4

Scientists working with the American Meteorological Society are conducting a study to determine whether this extreme weather event is caused by natural variability or human-caused climate change. A 2012 study found that a drought from that same year was primarily due to natural variation. However, the study also indicated that climate change was a factor in the heat waves that occurred during the spring and summer months.9 Scientists are unsure whether to attribute the drought to natural variation, climate change, or a combination of both for this weather event. Long term precipitation changes are particularly difficult to predict, especially for mid-latitude countries such as the United States. One factor that cannot be overlooked is the loss of the ozone layer over the past century. Another study examined forest mortality by considering different levels of ozone exposure.10 The study established a correlation between the diminishing ozone layer and increasing global temperatures, determining that regions exposed to high levels of ozone were deemed vulnerable to increased droughts and fires.10 These findings should be a great concern for California officials and to the forests in the state.

Dry bed of Folsom Lake
Figure 5. Photograph on the shore of Folsom Lake when the reservoir was filled to only 18% capacity.
Photograph by Robert Couse-Baker, 2014. CC BY 2.0.

California officials are employing lessons learned during the 1970s drought to understand how to conserve the public water supply. One lesson state officials learned is that the general public can help in conservation efforts. The coastal community of Goleta was provided with low-flow shower heads and other water saving devices and reduced water consumption by thirty percent, which was double the expected reduction.11 California’s total population has increased by 18 million since the 1970s drought period and many conservation programs from that era will need to be updated to properly manage the water supply.12 The current mindset of punishing citizens for not conserving water should be amended to instead reward citizens for conserving water. This will make water conservation efforts more successful.


  1. Caldwell, P. (2010). California Wintertime Precipitation Bias in Regional and Global Climate Models. Journal of Applied Meteorology and Climatology, 49: 2147-2158.
  2. Onishi, N. & Wollan, M. (2014 January 17). Severe Drought Grows Worse in California. The New York Times.
  3. Wang J. & Georgakakos, K.P. (2004). Validation and Sensitivities of Dynamic Precipitation Simulation for Winter Events over the Folsom Lake Watershed: 1964-99. Monthly Weather Review, 133: 3-19.
  4. Goodale G. (2014 January 21). California drought: Scientists puzzled by persistence of blocking “ridge.” The Christian Science Monitor.
  5. Kim, J. et. al. (2012). Effects of atmospheric river landfalls on the cold season precipitation in California. Climate Dynamics, 40: 465-474.
  6. Martin, K. (2014 January 12). The California Drought Finally Explained With Both Upper and Lower Levels of Atmosphere to Blame.
  7. MacDonald, G.M. (2007). Severe and sustained drought in southern California and the West. Quaternary International, 173-174: 87-100.
  8. MacDonald, G.M. et. al. (2008). Southern California and the perfect drought. Quaternary International, 188: 11-23.
  9. Lochhead, C. (2014 January 22). California drought: Scientists to probe cause. The San Francisco Chronicle.
  10. Panek, J. et. al. (2013). Ozone distribution in remote ecologically vulnerable terrain of the southern Sierra Nevada, CA. Environmental Pollution, 180: 343-356.
  11. Warren, J. (1991 February 19). Lessons of the 1970s Shape Water Rationing Plans. Los Angeles Times.
  12. Fimrite, P. (2014 January 19). California drought: Water officials look to rules of ’70s. The San Francisco Chronicle.
  13. Cortopassi, Kevin. (2014). Sacramento Capital During the Drought. [Photograph]. Retrieved from FlickrCommons. CC BY-ND 2.0.
  14. National Drought Mitigation Center. (2014). Progression of the 2012-2014 historic California drought, from December 2013 to July 2014. [Animation]. Retrieved from Wikimedia Commons. Public Domain.
  15. California Department of Water Resources. (2014). [Photograph of Lake Folsom Before and During the 2012-14 North American Drought]. Retrieved from Public Domain.
  16. NASA/NOAA. (2014). [Photograph from space comparing the Sierra Nevada snowpack in 2013 and 2014]. Retrieved from Public Domain.
  17. Robert Couse-Baker. (2014). Dry Folsom. [Photograph] Retrieved from FlickrCommons. CC BY 2.0.


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