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CCM Question 1

CCM Question 1. Geoff Roest MO 590/790. Question. Home builder in Southern California San Gabriel Mountains Using unpaved access roads while building Concerned about washouts Wants to know Are news reports regarding PDO and rainfall true? Consultant’s views on these issues. Question.

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CCM Question 1

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  1. CCM Question 1 Geoff Roest MO 590/790

  2. Question • Home builder in Southern California • San Gabriel Mountains • Using unpaved access roads while building • Concerned about washouts • Wants to know • Are news reports regarding PDO and rainfall true? • Consultant’s views on these issues

  3. Question

  4. PDO Pacific Decadal Oscillation (PDO) – variation in sea surface temperature in North Pacific Prominent report – LaDochy et al Claims correlation between PDO and rainfall in Southern California is statistically significant

  5. PDO • I calculated the correlation using seasonal rainfall (July 1 to June 30) in Los Angeles for period of 1948 to 2003 • Correlation coefficient = 0.08 • Explains 0.64% of variance • For sample size of 57 years – 45% confidence level • Correlation between PDO and seasonal rainfall in Los Angeles is not statistically significant

  6. PDO

  7. ENSO • Southern Oscillation Index (SOI) – based on sea level pressure at Darwin and Tahiti • Correlation between seasonal rainfall in Southern California and SOI is > -0.5 • Explains > 25% of variability • Meets 99.9% confidence level • Correlation between seasonal rainfall in Southern California and SOI is statistically significant

  8. SOI

  9. ENSO • Nino 3 – based on sea surface temperature anomalies • Correlation between seasonal rainfall in Southern California and Nino 3 index is > 0.5 • Explains > 25% of variability • Meets 99.9% confidence level • Correlation between seasonal rainfall in Southern California and Nino 3 index is statistically significant

  10. Nino 3

  11. Nino 3

  12. Answer • Negative PDO is not good indicator of rainfall during next 5 years • Correlation not statistically significant • ENSO not good indicator • Well correlated, but not well forecasted • My suggestion: identify threshold rainfall recurrence rate that the temporary access roads should withstand • i.e. 100 year event (1% chance of occurring each year) • If roads are well constructed, more likely to avoid washouts

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