Development of a Precipitation-Area Curve for Warning Criteria of Short-Duration Flash Flood
Abstract. This paper presents quantitative criteria for flash flood warning that can be used to rapidly assess flash flood occurrence based on only rainfall estimates. This study was conducted for 200 small mountainous sub-catchments of the Han River basin in South Korea because South Korea has recently suffered many flash flood events with short duration. Flash Flood Guidance (FFG) was defined as the depth of rainfall of a given duration required to cause minor flooding at the outlet of a small stream basin and was estimated using threshold runoff (TR) and antecedent soil moisture conditions in all the sub-basins. The soil moisture conditions were estimated during the flooding season, i.e., July, August and September, over 7 years (2002~2009) using the Sejong University Rainfall Runoff (SURR) model. A ROC analysis was used to obtain optimum rainfall values and a generalized precipitation-area curve (P-A curve) was developed for flash flood warning thresholds. The threshold function was derived as P-A curve due to the reason that the precipitation threshold with short duration is highly related to basin area than any other variables. Generalized thresholds for flash flood warning were obtained for rainfall rates of 42, 32 and 20 mm/h in sub-basins with areas of 22~40 km2, 40~100 km2 and > 100 km2, respectively. The proposed P-A curve was validated based on actual flash flood events in different sub-basins, which showed the viability of the proposed criteria to capture actual flash floods using only the rainfall rate and area of a sub-basin. The key advantage of this method is possible to issue flash flood warnings without the need to run entire hydro-meteorological model chains in the region where the short-duration flash flood frequently occurred.