Comparative Study on Spatiotemporal Characteristics of Fixed-Area and Storm-Centered ARFs

Abstract

In the design flood estimation procedure, the areal reduction factor (ARF) is used to convert ground-level point rainfall records into areal design rainfall for a reference area. Practically, the ARF is estimated through the fixed-area (ARFfa) scheme but has limitations as a statistical approach based on sparse ground-observation density. The ARFfa indicates potential biases because of the unsynchronized frequency analysis between point and areal rainfall. The storm-centered ARF (ARFsc) is obtained directly from individual storm captured by high resolution radar. In this study, the ARFsc values were estimated during the monsoon season (June to September) during 2007–2012 that covered the entire nation of South Korea, and then expressed as a function of reference area, duration, and return period. Both the ARFfa and ARFsc are proportional to the reference area. However, the most distinct difference is their responses to the return periods. For the fixed specific duration, the ARFfa indicates insensitive response to the return period over the reference area, whereas the ARFsc indicates quite varied declining rates according to the return periods. The ARFfa’s invariant characteristics arise from its statistical scheme assuming identical distributions with similar shape parameters for the point and areal annual maximum rainfalls. The results can be used to avoid excessively conservative designs and assist in more economic and reliable uses of practical areal reduction factors. DOI: 10.1061/(ASCE)HE.19435584.0001839. This work is made available under the terms of the Creative Commons Attribution 4.0 International license, http:// creativecommons.org/licenses/by/4.0/.