Role of Snowmelt in Determining whether the Maximum Precipitation Always Results in the Maximum Flood

Abstract

In snow-dominated regions surface air temperature is expected to have a substantial effect on the magnitude of a flood during a storm event. It is risky to estimate the design flood based only on the maximum precipitation while excluding other atmospheric variables like temperature and radiation. To overcome this problem, a methodology to estimate the maximum flood is proposed based on a physically based hydrologic model with input from physically maximized storm events by means of a numerical atmospheric model. As a case study, the probable maximum floods are simulated for the Upper Feather River watershed, the Yuba River watershed, and the American River watershed that are located in a mountainous region in Northern California, from the most severe 60 historical precipitation events during 1951–2010 for each watershed. The results show that this methodology can explain the underlying physical causes for the occurrence of maximum precipitation. It also shows that the maximum precipitation, determined in terms of the maximum areal average precipitation depth over a selected watershed during a selected storm duration, does not necessarily produce the maximum flood over that watershed.