Flood flow simulation using CMAX radar rainfall estimates in orographic basins

Abstract

Rapid flood forecasting in orographic basins generally relies on hydrologic models. Rainfall is one of the most critical parameters in hydrologic models, and the spatial distribution of rainfall over a basin is required for accurate flood forecasting. Gauged rainfall is measured at ground stations; however, the resolution of the spatial rainfall distribution is limited by the number of available stations. In contrast, the use of weather radar to detect rainfall offers a significant analytical improvement in temporal and spatial resolution. The constant altitude plan position indicator (CAPPI) has been widely employed for precipitation nowcasting and flood prediction. The column maximum (CMAX) has been used to inform meteorologists about severe thunderstorms, and its use to predict hydrologic flood forecasting has great promise. Therefore, the purpose of the current study is to present the applicability of CMAX to hydrological flood forecasting, especially in orographic basins. Two radar rainfall estimates, comprised of CAPPI and CMAX, were compared to determine the actual spatial distribution of rainfall over a basin in the southern part of South Korea, and hydrologic flood forecasting was computed using a physics-based distributed hydrologic model. The results show that the CAPPI underestimates the accumulative rainfall, while the CMAX reproduces the observed accumulative rainfall relatively well for Nam river dam basin in South Korea. In addition, the CAPPI-estimated runoff is low compared to the observed hydrograph, while the CMAX-estimated peak discharge, total volume, and peak time are estimated well. The results reveal that the CMAX provides useful information for hydrologic flood forecasting.