HAPpy Hour: Historical and Future Changes in Extreme Precipitation Across the Northeastern United States

Abstract- The northeastern United States has experienced a dramatic increase in extreme precipitation over the past thirty years, yet the evolution and drivers of this increase, as well as how Northeast precipitation will evolve by the end of the21st century, remain uncertain. To assess historical changes in extreme precipitation, we analyzed station observations from the Northeast for multiple time periods spanning 1901–Present, finding that extreme precipitation 1996–2014 is 53% higher than 1901–1995.  To identify the mechanistic drivers of this increase, we used daily weather maps to classify extreme precipitation events by meteorological cause and reanalysis data to determine large-scale changes in the atmosphere and ocean associated with increased extreme precipitation for each classification, finding that tropical cyclones account for almost half of the post-1996 extreme precipitation increase, with enhanced precipitation from tropical cyclones after 1996 coincident with warmer Atlantic sea surface temperatures and higher total column water vapor.  To examine the future of precipitation across the Northeast, we used the Weather Research and Forecasting (WRF) regional climate model driven by the National Center for Atmospheric Research Community Earth System Model (CESM) to simulate precipitation for historical (1976-2005)and future (2070-2099) periods, finding an increase in both total (10%) and extreme (52%) precipitation by the end of the 21st century.  These results are consistent with additional WRF simulations forced with the Max Planck Institute Earth System Model and the North American Coordinated Regional Downscaling Experiment archive.