Assessment of antecedent moisture condition on flood frequency: An experimental study in Napa River Basin, CA

Abstract

Study regionThis study region is the Napa River basin in California whose antecedent soil moisture states and precipitation magnitudes are primary drivers to occur extreme floods. Study focusThis study assessed the influence of antecedent moisture condition on flood frequency, based on an experimental application scheme and pre-processing. For this purpose, T-year flood simulations were conducted using a distributed hydrologic model. Distributed precipitation patterns which have an amount of precipitation corresponding to a specific T-year return period were generated by representative radar-based precipitation fields and precipitation frequency analysis. Dry, normal, and wet of antecedent moisture condition were applied to each T-year flood simulation to reflect variable initial soil moisture states. New hydrological insights for the regionThe relationship among flood frequency, antecedent moisture condition, and precipitation frequency was derived for a specific target storm event. For normal antecedent moisture states, the relation showed that T-year precipitation could generate floods having return intervals nearly identical to those derived using gage records. For saturated soil conditions, a 7-year precipitation event could trigger a 100-year flood. Conversely, a 200-year precipitation event with dry soil conditions might generate only a 15-year flood event. The results emphasize the importance of soil moisture to flood runoff and suggest that soil-moisture monitoring could aid in improving flood forecasting.