Author(s): Eunji Kim, Boosik Kang
Keywords: Areal reduction factor; Fixed-area ARF; Storm-centered ARF; Climatic characteristic;
Abstract: The areal reduction factors (ARF) is the key parameters in engineering design procedures reflecting spatial distribution of storm event. In general, ARF is known to vary with reference area, storm duration and size of storm event, which has been estimated based upon the independent simple statistical analysis between point and areal rainfall under specific duration and frequency. The conventional ARF gives same value for the same reference area regardless of the storm types. In this paper, the ARFs of two regions with different climatic characteristics (Han-river basin in South Korea and Xe Namnoy basin in Laos) were estimated for duration 1, 3, 6, 12, and 24 hours. Since the density of Xe Namnoy’s rain-gauges is sparse, so the reference area was fixed at catchment area of Xe Namnoy (521.58 km2). The fixed-area ARF was estimated using rain-gauge data, and the exceedance probability of maximum storm intensity of individual event was estimated under the assumption of Gumbel distribution. For the Han-river basin, the storm-centered ARF based on radar rainfall data was estimated and used for comparison with the fixed-area ARFs. The Korea Meteorological Administration (KMA) provides a quality-controlled nationwide composite radar images with 1-km resolution every 10 minutes which are effective in capturing spatial distribution of storm events and were used for estimating ARFs for storm events in the flood season (June to September) during 2007 – 2012. Three types of ARF were analyzed the relationship between duration and return period and compared the differences.