Analysis of Widespread Heavy Precipitation Events

Using MERRA2 reanalysis and TRMM data, this study aims to quantify the distribution and characteristics of widespread heavy rainfall events around the globe. Widespread precipitation is here defined as rainfall exceeding the 99^th percentile for the period of record (1998 – 2016) over a 1.5 x 2 degree latitude-longitude box. This size of bounding box is small enough to provide a good sample size but large enough to exclude the smaller scale events that are beyond the purview of this study. Values of important meteorological parameters such as precipitable water and upper level winds, among others, are analyzed to determine quantitatively the “fingerprint” of such events; as well as regional thresholds for particular variables and combinations of variables that must be surpassed for an event to occur. At present this analysis is limited to the United States east of the Rocky Mountains, with the goal of extending it world wide. Knowing these thresholds, trends in the variables found to be most important are investigated through the length of the dataset. In a changing climate, changes in precipitation must be understood to quantify impacts to humanity.  Understanding the distribution and characteristics of widespread heavy precipitation events quantitatively, and determining how likely threshold values for such events will be met or exceeded in the future, will allow decision makers the tools they need to develop mitigation plans.