When I read about megadroughts and massive floods in California’s prehistory a year and a half ago, I didn’t know if this was generally accepted as science. California’s drought has now stretched into its fourth year. The New York Times reported California megadroughts two decades ago, and a recent State of California report discusses long droughts from California’s prehistory. Looks like long droughts are accepted as science; now let’s see how we deal with the new normal.
My post about The West Without Water concludes with “Megadroughts and flooding the Central Valley for months is scary stuff, and then there’s recent climate change! Are these megadroughts and floods credible?”
This week the New York Times (NYT) published an article “A Wet Era May Be Ending“. Our rainfall history of past 100-150 years is brief in a geologic sense and has been during a wet period, so projections based only on this brief history can be misleading. Speaking about drought, California’s governor said “This is the new normal, and we’ll have to learn to cope with it.” The article has a nice graph showing drought severity since 1 AD. The caption reads “Analysis of tree rings suggests that western states have had many droughts of two decades or longer, including two megadroughts lasting longer than 100 years.” From the article,
In the 1990s, Scott Stine, a professor at what is now called California State University, East Bay, took advantage of a decline in the levels of Mono Lake and other lakes and streams in the eastern Sierra Nevadas to study tree stumps, still rooted in the ground, that had become visible after having been submerged for hundreds of years.
At some point, water levels must have been low enough for long enough for the trees to grow. By dating the stumps using radioactive carbon techniques and noting their elevations, Dr. Stine was able to reconstruct the ancient water levels and thus the drought history of the area.
A NYT report of California megadroughts seems authoritative, that the science and conclusions are real. To learn more about Scott Stine, I did a search; the search results point to a 1994 NYT article “Severe Ancient Droughts: A Warning to California“.
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, new studies of past climates show. The findings suggest, in fact, that relatively wet periods like the 20th century have been the exception rather than the rule in California for at least the last 3,500 years, and that mega-droughts are likely to recur.
Long droughts in California, reported 21 years ago by the New York Times! I had no idea.
In February the California Department of Water Resources published California’s Most Significant Droughts, an excellent primer on California water supplies and drought. From Chapter 2,
A period of historically recorded hydrology of little more than a century does not represent the full range of the climate system’s natural variability. Paleoclimate information, such as streamflow or precipitation reconstructions developed from tree-ring chronologies, provides a long-term perspective on climate variability. Perhaps the earliest recognition of the relative severity of earlier paleodroughts dates back to the modern drought of 1929-34, when Lake Tahoe dropped below its natural rim and exposed tree stumps rooted in place on the lake bottom.
The State of California acknowledges that looking only at written history is not adequate and our climate is more variable than history indicates. We need to consider paleoclimate information that includes long droughts in California’s past. Now let’s see how we deal with the new normal.