Statistical model for assessing the risk of hail damage to any ground installation. Technical report, June 1978-March 1979

Abstract

This report describes a statistical model which has been developed to determine the risk of damage by large hail to any ground installation (such as a solar flat plate collector). The model is based on data for the number of haildays per year, hailstone size distribution, and storm severity (expressed in number of hailstones per square meter per storm). Other than parameters derived from the raw meteorological data available, the parameters of the model are the number of years of surface exposure and the exposure area size. The end result is the probability of a hailstone of a given size striking a given surface area in a given number of years. The maximum probable hailstone size is used as a convenient index of hail risk. The data upon which to base a prediction model are sparse at this time, covering few geographic locations; much of the information available is deficient in sampling consistency and/or sample size. For this reason, this report fully documents the derivation and use of the model for future applications, when more and better data are collected. The FORTRAN source code to calculate the risk model digitally is included in APPENDIX D. This model improves on previousmore » work in: (1) the use of more thorough statistical procedures and a more rigorous accounting of storm severity; (2) a more thorough investigation into the two probability density distributions commonly used (Poisson and negative binomial) to describe hailday frequencies, and (3) an attempt to define more rigorously the distribution of hailstone sizes. A sensitivity analysis was performed and conclusions are drawn from the results.« less