Steve Ladochy, Pedro Ramirez, Dan Killam, Ann Bui, William Patzert, Josh Willis

American Meteorological Society

Published date January 1, 2011

Temperature and Precipitation Trends in California: Global Warming and Pacific Ocean Influences

  • Analyzes data spanning a period from approximately 1900 to present to establish the relationship between Pacific oceanic and atmospheric annual and decadal variations and California temperatures and precipitation
  • Uses temperature and precipitation monthly and annual data from 1895 to present were acquired for the eleven California climate divisions from the Western Regional Climate Center, Desert Research Institute, Reno, NV California
  • Calculates temperature and precipitation anomalies based on deviations from the long-term (1901-2009) average
  • Calculates trends in annual and seasonal precipitation as well as trends in intensities and frequencies of precipitation events
  • Finds that, for the period 1895 to 2009 California annual temperatures show rates of increases per century of 0.87, 0.61 and 1.14°C (1.57, 1.10 and 2.05°F) for mean, maximum and minimum averages, respectively
  • Finds, however, that these rates of warming actually increased more when using records from 1949 to present and 1975 to present
  • Finds that overall state averages since 1975 increased more than twice the longest record (1895-2009) in all three temperature categories
  • States that since about 1950, the northern regions record decreases in precipitation, while records of the southern regions show increases. Many climate studies use the more complete data record from the 1950-2000 period to document warming and increasing precipitation; (states that this period marks a distinct shift in Pacific Ocean conditions from the cold phase to the warm phase of the PDO)
  • States that the second half of the century at Sacramento displays less light rainfall and more moderate and heavy rainfall
  • States that the change in intensity is mostly focused in Northern California, though some Southern California stations such as Los Angeles show similar changes