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CCM Question 2

CCM Question 2. Question. Home owner in San Rafael is designing roof Wants roof to withstand 100 yr rainfall events 1-hr? 24-hr? Irrigation system must be tailored to average rainfall What is middle 67% of rainfall? Is map showing average rainfall of 36” per year correct?. Question.

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CCM Question 2

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  1. CCM Question 2

  2. Question • Home owner in San Rafael is designing roof • Wants roof to withstand 100 yr rainfall events • 1-hr? • 24-hr? • Irrigation system must be tailored to average rainfall • What is middle 67% of rainfall? • Is map showing average rainfall of 36” per year correct?

  3. Question • 1859 5th Ave, San Rafael, Marin County, California 94101 • Rainfall gauge at 37.972 lat, -122.525 lon • Daily rainfall data • 0.9 miles ESE of house • Rainfall gauge at 37.967 lat, -122.533 lon • Hourly rainfall data • 0.8 miles SE of house

  4. Question Locations of the homeowner’s address (marked by letter A), daily rainfall gauge (B), hourly rainfall gauge (C)

  5. Average • Average calculated from long term records of seasonal rainfall (July 1 to June 30) for period of 1878 to 2002, available from NCDC • Average = 36.33 inches per season • Close to map • Standard deviation – measurement of variability in seasonal rainfall • = 12.84 inches • 36.33 ± 12.84 inches • Middle 67% = 23.49 – 49.17 inches

  6. Return Periods • 100 year return period means, based on data, 1 event per 100 years of data will exceed that rate • 1% chance of occurring each year • Can occur more than once or not at all during any 100 year period • Climate change may make these values unrepresentative of present climate • Based on long term rainfall data

  7. Return Periods • 1-hr and 24-hr events with return period of 100 years • Calculated using same data • 100 year 1-hr rainfall event = 1.77 inches • 1977 to 1994 • 100 year 24-hr rainfall event = 8.55 inches • 1878 to 2002

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