At-Site Based Evaluation of Rainfall Estimates for Indiana

Abstract

An at-site based rainfall frequency analysis was performed using hourly precipitation data for 53 selected stations in Indiana. The combined use of generalized extreme value and extreme value type I distributions was found to provide the best statistics, and was applied to construct the at-site estimates. This at-site result was then compared to other commonly used regional rainfall estimates, including Indiana Department of Natural Resources rainfall, Huff and Angel rainfall, and National Weather Service Atlas 14. Non-negligible differences between at-site and regional estimates were found even though Indiana was previously reported as a homogeneous region for rainfall. Results suggest that discretion is necessary when using regional rainfall estimates for site-specific problems. The at-site estimate was also applied to compute the depth ratios between different durations. This ratio exhibited significant variability with increasing return period implying that the use of a constant depth ratio to estimate rainfall might not be appropriate for larger return periods.