# Detected changes in precipitation extremes at their native scales derived from in situ measurements

## TL;DR

This study analyzes high-resolution, in situ observed extreme precipitation changes across the contiguous US from 1950 to 2017, revealing significant seasonal variations, especially in fall, using advanced spatial statistical methods.

## Contribution

It introduces a novel approach to derive non-smoothed gridded estimates of extreme precipitation from station data, improving detection of pointwise changes over time.

## Key findings

- Significant fall (SON) changes in extreme precipitation affecting 33% of CONUS.
- Few meaningful pointwise changes detected in other seasons.
- Seasonal variability influences the detectability of precipitation extremes.

## Abstract

The gridding of daily accumulated precipitation -- especially extremes -- from ground-based station observations is problematic due to the fractal nature of precipitation, and therefore estimates of long period return values and their changes based on such gridded daily data sets are generally underestimated. In this paper, we characterize high-resolution changes in observed extreme precipitation from 1950 to 2017 for the contiguous United States (CONUS) based on in situ measurements only. Our analysis utilizes spatial statistical methods that allow us to derive gridded estimates that do not smooth extreme daily measurements and are consistent with statistics from the original station data while increasing the resulting signal to noise ratio. Furthermore, we use a robust statistical technique to identify significant pointwise changes in the climatology of extreme precipitation while carefully controlling the rate of false positives. We present and discuss seasonal changes in the statistics of extreme precipitation: the largest and most spatially-coherent pointwise changes are in fall (SON), with approximately 33% of CONUS exhibiting significant changes (in an absolute sense). Other seasons display very few meaningful pointwise changes (in either a relative or absolute sense), illustrating the difficulty in detecting pointwise changes in extreme precipitation based on in situ measurements. While our main result involves seasonal changes, we also present and discuss annual changes in the statistics of extreme precipitation. In this paper we only seek to detect changes over time and leave attribution of the underlying causes of these changes for future work.