The Evaporative Origin of Colorado’s Extreme Precipitation During the Summer of 2023

In 2023, most of Colorado’s northeastern plains experienced its wettest four-month period (May-August) out of 129 years of record (NOAA’s Monthly U.S. Climate Gridded Dataset). This extreme precipitation led to flash flooding, road washouts, and significant property damage among Colorado communities including Denver and Colorado Springs. Although much is known about the seasonality of precipitation in the state, less work has explored the evaporative origin of Colorado precipitation. To better anticipate and understand extreme precipitation events in eastern Colorado, we investigated the evaporative origin of 2023’s extreme precipitation and how it compares to moisture sources during the previous 22 years. Specifically, this study uses the Water Accounting Model 2 Layers (WAM-2layers) and ERA5 climate reanalysis data to quantify the sources of precipitation in eastern Colorado during 2023 and over the past 22 years. Our moisture source analysis reveals that (1) eastern Colorado typically receives its moisture from within Colorado, as well as the Gulf of California, the Pacific Ocean, and the Western United States, (2) the increase in precipitation in 2023 was likely attributed to a mix of both usual and unusual moisture sources, and (3) during May, the wettest month in 2023, terrestrial evaporation made up a greater proportion of precipitation compared to the past 22 years. This research provides valuable insight into the extreme rainfall in the summer of 2023, specifically the factors that drove this historic event.