Diurnal and Seasonal Variations in Flash Floods Across the Western United States

Abstract

A fundamental problem with flash-flood forecasting and the implementation of comprehensive safety measures has been the lack of detailed information regarding diurnal and seasonal variations, particularly over the western portion of the United States. This research initiates the analysis of the diurnal and seasonal patterns of flash-flood events over the western United States using the National Climatic Data Center (NCDC) Storm Data reports collected from 1 January 1981 to 31 December 2010. Our preliminary finding show the number of recorded flash-flood events has increased over time; an increase likely due to population growth. In addition, flash-flood events over the western United States predominantly occur in the summer months, likely as a result of convective heating. The major exception to this strong summer peak is California. Also, the largest number of reported flash-flood events occurred in the mid-afternoon to early evening with a peak occurring earlier than expected at approximately 1530 LST. The strong link to convective heating and the centralized peak time period of a flash-flood occurrence can provide useful insight into new forecasting techniques and emergency management deployment.