The frequency of flood events has been increasing across large areas of the central United States since the second half of the 20th century. Little is known about what is driving these changes, and the fundamental question we ask ourselves is: why? Using an observation-driven approach, we develop a statistical framework to attribute the changes in the frequency of flood peak events to changes in the climate system and to land use / land cover. We focus on 287 U.S. Geological Survey sites with at least 50 years of daily discharge measurements between the second half of the 20th century and the present. Our analyses are performed at the seasonal level and consider five predictors (i.e., precipitation, temperature, antecedent wetness conditions, agriculture, and population density). Results indicate that precipitation and antecedent wetness conditions are the strongest predictors, with the role of the latter that increases as we lower the threshold for the event identification. Furthermore, we highlight the role of weather types in explaining the observed changes in precipitation and, consequently, in the frequency of flood events.
The aim of this presentation is to provide insights into the possible reasons responsible for the changes in the frequency of flood events across the central United States, providing basic information that may enhance our capability of predicting and projecting these changes.