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.
Highlights
The scientific purpose of identifying the spatiotemporal distribution of rainfall clusters is to understand the evolutionary processes of different types of rainfall phenomena in different geographic layouts
The overall mean behavior of areal reduction factor (ARF) directly estimated from the real storm events follows the expected pattern, the high variability of ARF is the nature of Return period Regression
The scaling patterns are not always clear because of the nonlinear features, the results present that the spatial and temporal distribution of rainfall clusters should follow the rule that the scaling property governs the relationship among ARF, area, duration, and return period
Summary
The scientific purpose of identifying the spatiotemporal distribution of rainfall clusters is to understand the evolutionary processes of different types of rainfall phenomena in different geographic layouts. The ARF is defined as the ratio between the areal rainfall with a specific frequency and the point rainfall with the same return period within the same area—called the fixed area ARF (ARFfa). In the ARFfa method, the point and the areal rainfall have the same return period but do not occur naturally at the same time by definition. The rainfalls at the gauge sites within a clustered storm area do not have the same return period, and the ARFfa must be different from that estimated from a real storm cluster—the so-called storm-centered ARF (ARFsc). The main objective is to compare two different types of ARFs and discuss the relative feasibility of the ARFfa in terms of its duration, area, and frequency through the comparison with the ARFsc
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