CLIMATE OF SAN FRANCISCO
Rainfall Return Periods
Consecutive Minutes/Hours
Return Period 5 min 10 min 15 min 30 min 1 hr 2 hr 3 hr 6 hr 12 hr
2 years 0.17 0.24 0.29 0.39 0.53 0.74 0.90 1.26 1.68
5 years 0.23 0.33 0.40 0.53 0.72 1.01 1.22 1.71 2.29
10 years 0.27 0.38 0.46 0.62 0.83 1.17 1.41 1.98 2.65
25 years 0.31 0.44 0.54 0.71 0.96 1.35 1.64 2.29 3.07
50 years 0.34 0.48 0.59 0.78 1.05 1.48 1.79 2.51 3.36
100 years 0.36 0.52 0.63 0.85 1.13 1.60 1.93 2.71 3.63
200 years 0.39 0.56 0.68 0.91 1.21 1.71 2.07 2.91 3.89
500 years 0.42 0.60 0.74 0.98 1.32 1.86 2.25 3.15 4.22
1000 years 0.45 0.64 0.78 1.04 1.39 1.96 2.38 3.34 4.46
10,000 years 0.52 0.75 0.91 1.22 1.63 2.30 2.78 3.91 5.23

Consecutive Days
Return Period 1 2 3 4 5 6 8 10 15 20 30 60 365
2 years 1.87 2.54 2.96 3.34 3.64 3.94 4.46 4.92 5.96 6.70 8.03 11.84 20.96
5 years 2.61 3.58 4.15 4.66 5.08 5.49 6.24 6.82 8.09 9.12 10.87 16.13 28.21
10 years 3.09 4.26 4.92 5.50 6.01 6.49 7.35 7.97 9.33 10.56 12.52 18.60 32.57
25 years 3.67 5.11 5.87 6.53 7.14 7.69 8.68 9.33 10.77 12.22 14.41 21.42 37.67
50 years 4.10 5.73 6.56 7.27 7.96 8.56 9.63 10.29 11.75 13.37 15.70 23.35 41.23
100 years 4.51 6.33 7.23 7.99 8.75 9.39 10.54 11.20 12.68 14.45 16.92 25.15 44.60
200 years 4.91 6.92 7.89 8.69 9.52 10.21 11.43 12.08 13.56 15.49 18.07 26.86 47.84
500 years 5.43 7.70 8.75 9.60 10.52 11.27 12.57 13.21 14.68 16.81 19.53 29.00 51.97
1000 years 5.82 8.28 9.39 10.28 11.27 12.06 13.41 14.04 15.49 17.77 20.59 30.56 55.00
10,000 years 7.10 10.20 11.49 12.50 13.71 14.62 16.16 16.70 18.04 20.81 23.92 35.44 64.66
  • Example: A 6-hour - 100 Year storm (i.e., 6 consecutive hours of rain) with a return period of 100 years would statistically be 2.71 inches.
  • VERY IMPORTANT NOTE: A 100-year storm means that there is a 1-in-100 probability of a similar event in any given year.  It does NOT mean there is an interval of 100 years between events.
  • Special thanks to Jim Goodridge for this updated (July 2009) dataset of his original work: J. D. Goodridge, based on Goodridge, J. D. (1982). Rainfall Depth-Duration-Frequency for California, California Department of Water Resources, Sacramento. A detailed explanation of return period calculations can be found in Goodridge (1982) or Historic Rainstorms in California, A Study in 1000 Year Rainfalls (California Department of Water Resources, August 1997).

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