Influence of variable precipitation on coastal water quality in Southern California

Ryan H. Dwight, Joshua S. Caplan, Mitchell V. Brinks, Sandra N. Catlin, Guido Buescher, Jan C. Semenza

Research output: Contribution to journalArticlepeer-review

24 Scopus citations


Objectives: To examine the consequences of changing precipitation levels on southern California's recreational coastal water quality, and compare the responses of watersheds with differing levels of urban development. Methods: The geo-temporal relationship for six years (2000-2005) of precipitation levels, discharge rates for the ten primary waterways, and coastal water bacteria concentrations at seventy-eight southern California beaches were examined. Results: Precipitation levels, river-creek discharge rates, and coastal water bacteria concentrations were significantly correlated (p < 0.01) for all ten watersheds investigated. Water bacteria concentrations significantly increased with higher levels of precipitation across 95% of the seventy-eight beaches investigated. A heavily developed watershed had significantly higher median bacteria concentrations (186 cfu) in the adjoining coastal waters compared to an undeveloped watershed (10 cfu) of similar size. Conclusions: Precipitation and ensuing runoff strongly control the rate of polluted water delivered to most beaches in southern California. Variable precipitation generates a greater response in coastal water bacteria concentrations in developed watersheds compared to undeveloped areas. Projected declines in regional precipitation as a consequence of climate change may result in less contaminated water delivered to coastal waters, thus decreasing risk of water associated illnesses during winter months.

Original languageEnglish (US)
Pages (from-to)2121-2130
Number of pages10
JournalWater Environment Research
Issue number12
StatePublished - Dec 2011
Externally publishedYes


  • Climate change
  • Coastal water quality
  • Indicator bacteria
  • Precipitation
  • Recreational marine bathing
  • Urban runoff

ASJC Scopus subject areas

  • Environmental Chemistry
  • Ecological Modeling
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution


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