The Role of Narrow Cold Frontal Rainbands on Flooding in Urban Southern California

Justin Tang, Hilary McMillan

Narrow cold frontal rainbands (NCFRs) bring brief but intense periods of rain during wintertime extratropical cyclones in Southern California. Much is known about the meteorology behind NCFRs, but little is known about NCFRs that ties together the meteorology and hydrology of urbanized watersheds. In this study, we assessed the extent of flooding in urban Southern California caused by NCFRs. We first quantified the proportion of flood events caused by NCFRs between 1995 to 2020 by analyzing NEXRAD reflectivity data, flash flood warnings (FFWs) issued by the National Weather Service, and USGS streamflow data of NCFR events. Seeking to understand the hydrometeorological characteristics of NCFRs, we then performed a regression analysis and mapped the quantitative precipitation estimation (QPE) data. Our results show that NCFRs make up nearly 40 percent of urban flood events, and that there were significant geographical differences in hydrometeorological characteristics among the four watersheds that warrant further study.