Jeongwoo Hwang, Upmanu Lall 

In many cases, persistent or recurrent synoptic circulation patterns lead to multiple wet days that precede an extreme rainfall event. The joint occurrence of high antecedent rainfall and extreme rainfall defines a compound event that may pose a high risk for overtopping of aging dams. Our novel analysis assesses whether there are significant trends across the conterminous United States (CONUS) in the joint and individual occurrence of extreme daily precipitation and k-day antecedent precipitation extremes, for k=5 and k=30 days. We find significant trends in the mean and variance of annual maximum daily rainfall, and in the k-day antecedent precipitation in certain regions of the CONUS. However, their mutual dependence as measured through a copula is invariant with time. The probability of their joint exceedance, i.e., simultaneously experiencing high extremes of daily precipitation and the k-day precipitation total, is also increasing in many places in the CONUS.