California's Ongoing Droughts

California is no stranger to drought; it is a recurring feature of the state's climate. They recently experienced a five year event from 2012-2016; other notable historical droughts included 2007-09, 1987-92, 1976-77, and off-and-on dry conditions more than a decade in the 1920s and 1930s. Presently, they are in year three of a serious drought. ¹ Looking back in time it's evident that things could be much worse. Beginning about 1,100 years ago, what is now California baked in two droughts, the first lasting 220 years and the second 140 years. Each was much more intense than the mere six year dry spells that afflict modern California from time to time. ²

In Medieval times the California droughts coincided roughly with a warmer climate in Europe, which allowed the Vikings to colonize Greenland and vineyards to grow in England

The earlier droughts were not only much longer, they were far more severe than either the drought of 1928-1934, California's worst in modern times, or the more recent severe dry spell of 1987 to 1992. In Medieval times the California droughts coincided roughly with a warmer climate in Europe, which allowed the Vikings to colonize Greenland and vineyards to grow in England, and with a severe dry period in South America, which caused the collapse of that continent's most advanced pre-Inca empire, the rich and powerful state of Tiwanaku, recent studies have found. ² Dr. Scott Stine, a paleoclimatologist at California State University at Hayward, says that California, like Tiwanaku, presents 'a classic case of people building themselves beyond the carrying capacity of the land,' which is determined not by wet times but by dry ones. "What we've done in California is fail to recognize that there are lean times ahead," Said Dr. Stine, "and they are a lot leaner than anything we've come up against' in the modern era." (3) Kenneth Richard presents a recent review of a number of studies reporting that drought is now less common and severe than centuries ago. ⁴ The water levels dropped during these earlier periods, as much as 50 feet in some cases. The droughts were not only much longer, they were more severe than the drought of 1928 to 1934, California's worst in modern times, or the more recent severe dry spell of 1987 to 1992. Since 2000, the longest duration of drought in California lasted 376 weeks beginning on December 27, 2011 and ending on March 5, 2019. Note that all of the droughts since 1928 have been considerably less than the really long droughts from earlier times. ²

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Modern period has recorded no increasing drought trends relative to the last few thousand years

Many new drought reconstructions indicate the modern period has recorded no increasing drought trends relative to the last few thousand years. The periods 1931-1938 and 1909-1917 were the longest and most severe wet and dry periods. ⁵ Instead of being driven by increasing greenhouse gas concentrations and warming, droughts along the western coast of the United States are 'predominantly (84%) driven by internal atmospheric variability' and cooling sea surface temperatures. (6) All of this in an area that is 25% desert and has a population of 40 million.

References

1. "Our experts weigh in on drought," ppic.org. July 19, 2022
2. William K. Stevens, "Severe ancient droughts: a warning to California," nytimes.com, July 19, 1994
3. Scott Stine, "Extreme and persistent drought in California and Patagonia during Medieval time," Nature 369(6481), 546-549, June 1994
4. Kenneth Richard, “Several more new studies show drought is now less common and severe than centuries, millenia ago,” notrickszone.com, June 14, 2021
5. Liangjun Zhu et al., “Influence of the Atlantic Multidecadal Oscillation on drought in northern Daxing'an Mountains, Northeast China,” CATENA, 198, March 2021
6. Seung H. Baek et al., “USA Pacific coastal droughts are predominantly driven by internal atmospheric variability,” American Meteorological Society, 34, Issue 5, March 1, 2021