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):

  1. There had been no material change in the mean climatic conditions for 162 years
  2. The 40 years from 1890-1930 had fewer fluctuations from average conditions than did earlier years
  3. A 28-year drought ending in 1810 was about as severe as, and more protracted than, the drought occurring when this paper was written
  4. Both 1810-21 and 1883-93 had rainfall surpluses more intense than 1890-1930
  5. Rainfall deficiency from about 1822 to 1832 was more severe than anything experienced up to 1930
  6. The longest rainfall deficiency occurred from 1842 to 1883, though it was not as acute as other periods
  7. The drought occurring when this paper was written (1930) could not be considered a major shortage
  8. Water yield of the areas under consideration closely approximates run-off from principal streams
  9. Run-off fluctuations generally track rainfall fluctuations, but are larger
  10. 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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