# Trends in U. S. Storminess 1949--2009

## TL;DR

This study analyzes over 60 years of U.S. hourly precipitation data to identify trends in storminess, finding no significant increase or decrease in extreme weather event frequency or severity.

## Contribution

It introduces a robust statistical method to assess long-term trends in storminess using normalized variance of hourly rainfall across thousands of stations.

## Key findings

- No significant trend in storminess over 60 years
- Upper bounds on trend magnitude set at 0.001 per year
- Method confirms stability of extreme weather event frequency

## Abstract

We use an extensive NOAA database of hourly precipitation data from 5995 stations in the 48 contiguous United States over the period 1949--2009 to investigate possible trends in the frequency and severity of extreme weather events, defined as periods of intense precipitation. The frequency and intensity of these events are quantified by a dimensionless storminess, defined as the variance of the hourly rainfall at a site normalized by the square of the mean rainfall at that site. For 1722 stations with sufficient data, we compute the rate of change of the logarithm of the storminess at each station and set bounds on its mean (over stations) trend; use of the logarithms weights trends at calm stations equally to those at stormy stations and enhances the statistical power of the mean. These results are confirmed by reversing the order of averaging: first computing, for each year, the mean (over stations) logarithm of the storminess, and then fitting to its trend. We set $2\sigma$ upper bounds of 0.001/y (doubling or halving time scales $> 1000$ y) on any trend, increasing or decreasing.