Advancing Flash Flooding Early Warning Using a Proxy for PAR Observations

The high spatiotemporal resolution of the rainfall rates is essential for flash flood forecasting, especially in urban environments that respond to the causative rainfall on the order of minutes. The conventional WSR-88D radars provide rainfall intensities in approximately five minutes, and may miss peak rainfall in severe-weather events that develop and evolve very rapidly. The phased-array radar (PAR) technology, a potential next-generation weather radar, is at least 4-5 times faster than the scanning rate of WSR-88D. To explore the ability of such high-frequency PAR observations to advance flash flood early warning, hydrologic studies have been conducted by using a proxy of PAR observations collected by WSR-88D KOUN polarimetric radar adopting a rapid-scanning strategy. The results show that the runoff generated by rapid-scan KOUN QPE at 1-min temporal resolution better matches stream gauge observations than that generated by traditional WSR-88D 5-min QPE. The unit runoff using fast-scan KOUN data shows higher maximum values, indicating better capability to capture flash flooding. These results highlight the benefit of PAR’s rapid-scan capability in flash flood early warning.