Long-term variability in atmospheric moisture transport and relationship with heavy precipitation in the eastern USA

This study investigates variability in moisture transport patterns within the eastern USA and adjacent Atlantic Ocean during the twentieth and early twenty-first centuries and relates these patterns to heavy precipitation. Daily integrated water vapor transport (IVT) from the European Centre for Medium-Range Weather Forecasts ERA-20C reanalysis for the eastern USA (30 degrees-50 degrees N x 60 degrees-90 degrees W) from 1900 to 2010 is classified into previously defined moisture transport patterns. Over the 111-year study period, annual counts of the high-IVT patterns increase at the expense of low-IVT pattern counts, with the rates of these changes varying by pattern and by season. Additionally, the frequency of intense IVT patterns persisting for consecutive days increases and weak IVT patterns are interrupted more frequently. Moisture transport in each of the patterns increases over the study period, particularly in the highest percentiles of IVT, indicating an intensification of IVT in the eastern USA. This intensification is expressed in the moisture transport patterns with spatial and seasonal variability. When heavy precipitation days from 1900 to 2010 from eleven stations are related to the water vapor transport patterns, several patterns emerge as major contributors to the regional heavy precipitation regimes within the study area. Over the study period, the occurrence of heavy precipitation increases with meridional, high-IVT patterns and decreases with frequent, zonal patterns. This indicates an increasing influence of synoptic-scale meridional moisture transport on heavy precipitation across the eastern USA. This study demonstrates the utility of a moisture transport approach to contextualize regional precipitation shifts within the changing global hydroclimatic system.

Automated summary

This study investigates the variability in moisture transport patterns in the eastern USA and adjacent Atlantic Ocean during the twentieth and early twenty-first centuries, and their relationship with heavy precipitation. The study finds that high-IVT patterns increase while low-IVT patterns decrease over the study period, with rates of change varying by pattern and season. The study also shows an increase in the frequency of intense IVT patterns persisting for consecutive days, as well as interruptions in weak IVT patterns. The moisture transport in each pattern increases over time, particularly in the highest percentiles of IVT, suggesting an intensification of moisture transport in the eastern USA. The study identifies several moisture transport patterns as major contributors to regional heavy precipitation regimes, with meridional, high-IVT patterns increasing heavy precipitation and frequent, zonal patterns decreasing heavy precipitation. The study highlights the importance of using a moisture transport approach to understand regional precipitation shifts in the changing global hydroclimatic system.