Drought In California – A Historical Perspective
By Paul Homewood
As we know, California is going through a serious drought at the moment. But how does it compare with earlier droughts in the 20thC? Let’s start by checking the rainfall stats for the last 12 months, August to July.
This last 12 months is the third driest August – July on record, behind 1976/7 and 1923/4.
One of the things that has exacerbated the drought is that we have now had three dry years on the trot. When 3-year trends are plotted, the latest period is slightly drier than 1974-77 and 1928-31.
However, looking at the longer term 60-Month chart, the longest NOAA provide, we find that many previous periods have been much drier. Perhaps the most serious and long running drought was during the 1920’s and 30’s.
The blue lines, by the way, are trends lines (not means). As the legend shows, precipitation trends are basically flat across the record.
What about reservoir levels?
California’s Dept of Water Resources provides a useful, and up to date, monitor.
http://cdec.water.ca.gov/cdecapp/resapp/getResGraphsMain.action
Each reservoir can be clicked on for more details, so, for instance, Folsom:
The data only goes back to 1976, and different years can be plotted. However, the default shows the driest, 1976/7, and the wettest, 1982/3. We can see that reservoir levels are comfortably higher currently than in 1977.
NOAA indicate that it is central California that is worst affected, so let’s take a look at a few more reservoirs in that region.
While the current drought is extremely serious, it is clear it is not “unprecedented”.
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NOT A LOT OF PEOPLE KNOW THAT 
Reblogged this on the WeatherAction Blog and commented:
There’s 76/77 (polar vortex year) again.
. . and on a longer time scale, even less unprecedented:
http://www.mercurynews.com/portlet/article/html/imageDisplay.jsp?contentItemRelationshipId=5689627
Water level in the Great Salt Lake of Utah is another place people look at when considering drought versus wet in the western US. During extremes it will be the cover story on publications — magazines such as National Geographic. Current level is low but not extremely so.
[The story on the west coast (northern part) this year is the great run of salmon – a PDO related event if the “experts” have it right.]
Salt Lake graph to Aug. of 2007:
Click to access GSL.WSAlt.Aug07.pdf
The early 1960s had a low stand and national magazines and news reports reported the “tragedy” – the mid-80s had a high stand and water ran in the streets of the city, and national magazines and news outlets reported the “tragedy.” Now it is low again.
On the main page I entered 2007 for the year (default seems to be the last 7 days) and after about 30 seconds of processing got a graph showing a 2012 high and a current low. This low is about 2 feet higher than the low recorded in the 1960s.
Paul, thanks for showing the data. It shows a problem, not a catastrophe.
What is unprecedented then, is the loudness of the call to stop producing CO2 to stop the drought, As if that could happen.
Reservoir levels are based on both inflow and outflow. It would be likely that during periods of less rainfall the drawdown would be greater. It would seem from the data that California reservoirs are indeed half empty most of the time