Extended Abstract (104K)P1.3
Analysis of Twenty-Five Years of Heavy Rainfall Events in the Texas Hill Country
Amy Schnetzler, Univ. of Missouri, Columbia, MO; and P. S. Market and J. W. Zeitler
Twenty-five years of daily (24-hour) rainfall data were examined for the Texas Hill Country using observations from 86 cooperative climate stations in the region; the period examined for this study was 1982-2006. Days with measurable precipitation were treated as a gamma distribution in order to determine the top 2%, 1%, and 0.5% to define events as unusual, rare, and extreme, respectively. This approach was applied to each station as well as to the aggregate data for all 86 stations, resulting in an analysis of 130,986 observations of 24-hour precipitation; for the aggregate gamma distribution, the parameters values of α = 0.4678 and β = 1.0082 were obtained. While individual stations varied greatly, the aggregate data yielded a 24-hour rainfall threshold of 67 mm (2.64 in) for an observation to be in the upper 2%, 82.6 mm (3.25 in) to be in the upper 1%, and 101.1 mm (3.98 in) to be in the upper 0.5% of the distribution. Over the course of 25 years, 127 days were found on which at least five (5) stations in the region had a 24-hour rainfall total that would be in the top 2% (or higher). Of these, only four (4) were the direct result of a tropical cyclone.
From this sample, rainfall amounts were also calculated for each station that represent 25-, 50-, 100-, and 200-year return frequencies.
Work presently underway seeks to arrive at synoptic types as have been defined by previous investigators; composites for each category will then be calculated.
Poster Session 1, Weather to Climate Scale Hydrological Forecasting
Monday, 21 January 2008, 2:30 PM-4:00 PM, Exhibit Hall B
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