Climate Controls on the Extreme Rainstorms in the Contiguous US: 1979-2015

Extreme rainstorms bring huge societal and economic loss around the world every year, and they have become more frequent and severe in the past several decades. Within the engineering community, atmospheric model-based storm maximization approach is being attempted for updated Probable Maximum Precipitation (PMP) estimation. However, there is currently a lack of information on how the extreme storm magnitudes are controlled by key meteorological conditions. With the projected changes of climate and land use in the upcoming century, it is increasingly important to understand the future of extreme storms. In this study we focused on the extreme rainstorms over the Contiguous US (CONUS) from North America Regional Reanalysis project, and investigated the triggers of such extreme events. Specifically, we looked into the impact of air moisture, atmospheric instability and horizontal air convergence. Our evaluation suggests that the most severe storms between 1979-2015 are usually triggered by extreme conditions in air moisture or horizontal air convergence, while atmospheric instability does not play significant roles in the storm initialization and evolution. These triggering roles also show geographical patterns: coastal storms are usually caused by extreme moisture/air convergence, while inland storms tend to occur under extreme atmospheric instability. With a better understanding the extreme rainstorms in the CONUS, engineering communities can now determine the meteorological factors that require to be controlled to physically model PMP estimates using numerical models.