Rainfall and Stream Run-off (1769-1931)
Rainfall and stream run-off data from California's Spanish Mission period, beginning in May 1769, through 1930, the date this was written, are analyzed in Rainfall and Stream Run-off in Southern California Since 1769 [PDF*, 9.2 MB] by H. B. Lynch (1931). The data apply to Southern California. Ten conclusions are reached (summarized and paraphrased here):
- There had been no material change in the mean climatic conditions for 162 years
- The 40 years from 1890-1930 had fewer fluctuations from average conditions than did earlier years
- A 28-year drought ending in 1810 was about as severe as, and more protracted than, the drought occurring when this paper was written
- Both 1810-21 and 1883-93 had rainfall surpluses more intense than 1890-1930
- Rainfall deficiency from about 1822 to 1832 was more severe than anything experienced up to 1930
- The longest rainfall deficiency occurred from 1842 to 1883, though it was not as acute as other periods
- The drought occurring when this paper was written (1930) could not be considered a major shortage
- Water yield of the areas under consideration closely approximates run-off from principal streams
- Run-off fluctuations generally track rainfall fluctuations, but are larger
- Useful water yield for Southern California has been 50% of average for a period of ten years, and 70% for a period of 28 years (within the dates studied)
This paper may be useful for students of historical water yield in California.
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