HBCU-Excellence in Research: Improved Understanding of the Changing Seasonality and Magnitude of Precipitation Extremes in the Eastern United States

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Extreme precipitation events pose numerous threats to life and property, thus characterization of their frequency and magnitude is of both scientific and societal interest. But such characterization is not easy given that extreme events are, by definition, rare. For example a "100 year flood" is a flood so large that it is unlikely to occur more than once a century (formally, it has less than a one percent chance of happening in any given year). A further consideration is that extreme precipitation likelihood is affected by the season and by climate variations such as El Nino events, and also changes over time as a consequence of global warming. In regions affected by landfalling hurricanes it is also important to separately assess their contribution to extreme precipitation, given the many ways in which hurricanes differ from other rain-bearing storms.Work performed here uses a variety of statistical techniques to estimate the frequency and magnitude of extreme precipitation events over the eastern US. One set of tasks seeks to characterize the seasonality of extreme precipitation, with the understanding that extreme event timing is often multimodal and may not align well with pre-defined seasons. The seasonality of extremes is assessed using a circular density approach in which the annual cycle is mapped to the unit circle and the timing of extreme events over the course of the year is represented by an angle-dependent probability density. A second set of tasks evaluates secular changes in probability distributions using quantile regression models, and further investigates the effects of large-scale climate patterns on precipitation probabilities. Additional work evaluates the impact of hurricanes on statistics of extreme precipitation in the study domain.The work has broader impacts due to the value of extreme event statistics for anticipating and mitigating precipitation-related hazards. The PIs have a specific focus on stormwater management as a transportation issue, and the project includes a review of standards for stormwater infrastructure design issued by state departments of transportation. In addition, the project provides paid summer research training to two undergraduate students who are also funded to attend the national meeting of the Council on Undergraduate Research. Student mentoring is also conducted through group meetings, presentations, written feedback, and a journal club. The project also provides support and training to a postdoctoral research associate.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.