Probability Density Functions of Daily Rain

Galiano Island Community School

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Year Probability Density Function of Total Daily Rain at Galiano Island Community School
Winter Probability Density Function of Total Daily Rain at Galiano Island Community School
Spring Probability Density Function of Total Daily Rain at Galiano Island Community School
Summer Probability Density Function of Total Daily Rain at Galiano Island Community School
Fall Probability Density Function of Total Daily Rain at Galiano Island Community School

Description

These plots show the Probability Density Functions (PDFs) of daily total rain at stations in the UVic School-Based Weather Station Network. The blue bars give the histogram of daily rain values (greater than zero) with bins of 1 mm. The red curve is the best fit to the histogram using a three-parameter gamma function. The orange and green vertical lines give the 95th and 99th percentile respectively. The number of days of rain and the percent of the total number of events that this represents are given in the last line of the legend.

The plots are shown for the entire year and for each season. The seasons are defined as follows:

  • Winter--January, February, March
  • Spring--April, May, June
  • Summer--July, August, September
  • Fall--October, November, December

The three parameter gamma function is of the form

The histogram is a count of events that fall into each bin. The number in each bin is then divided by the total number events and multiplied by 100 to convert it to percent. The rain gauges can measure rain in intervals of 0.25 mm.

References

  • Wilby, R.L. and T.M.L. Wigley, 2002, Future Changes in the Distribution of Daily Precipitation Totals Across North America
  • Bridges, T.C. and C.T. Haan, 1972, Reliability of Precipitation Probabilities Estimated From the Gamma Distribution. Monthly Weather Review, 100, 607-611
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Disclaimer:

Data from the School-Based Weather Station Network in Victoria, BC, Canada, are made freely available "as is" to the public with no guarantee of accuracy or availability. Commercial use requires a license. Please contact weather at ocean.seos.uvic.ca for more information.
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Last Modified: February 24 2012 13:59:49.