Spatial Characteristics And Frequency of Citizen-Observed Pluvial Flooding Events in Relation to Storm Size in Portland, Oregon

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Urban Climate

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Pluvial flooding is caused by intense rainfall events that overwhelm drainage systems and do not allow excess water to be absorbed by soils or water infrastructure. We examined the spatial characteristics of pluvial flooding in Portland, OR (2010–2017) by using citizen-reported flooding data. We used a spatially dense network of 5-min interval rainfall measurement to examine the relationship between the size of 3-day storm events and the frequency of flooding reports that were normalized by the population density at the census block group scale. Seventy percent of flooding reports were generated at smaller storm sizes of 5 cm or less over a 3-day period due to these storm sizes occurring more frequently across the observed time period. The flood reports were mainly clustered in the hilly west side, lower far north, central, and southeast regions of the city regardless of the time of year reports were generated. The flood reports were highest at the beginning of the wet season and decreased throughout the wet season. Flood reports were negatively associated with elevation variables. We recommend future research to minimize the potential caveats of using citizen-reported flooding data by creating better methods for standardizing and categorizing them


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