Characterizing the relationship between water vapor transport and associated regional precipitation in the eastern United States.

The frequency and magnitude of precipitation in the eastern United States is projected to change. Several reports and studies indicate that such changes have been observed in recent decades. To better understand these observed and projected changes in precipitation and to situate these changes within the contexts of climate variability and synoptic climatology, we investigate the water vapor fluxes to and within the eastern United States. This approach enables an understanding of changes in volume and trajectory of moisture transported through the atmosphere. Water vapor fluxes are represented by vertically-integrated water vapor transport (IVT) calculated from daily zonal and meridional vertically integrated vapor fluxes from ERA-Interim Reanalysis for 1979—2017 at 2.5° × 2.5° spatial resolution. By employing a machine learning self-organizing map methodology, sixteen distinct water vapor flux patterns were identified, encompassing the entirety of the regional atmospheric moisture fluxes. Analyses of the frequency, seasonality, and persistence of these flux patterns develop a climatology of water vapor transport for the eastern US. This climatology can be used to characterize the spatial and temporal variability of precipitation by its associated moisture fluxes. Daily gridded precipitation data are from PRISM at 4 km resolution, linking precipitation with water vapor fluxes across scales. The climatology of moisture flux patterns also reveals the role of atmospheric rivers in the northeastern US hydroclimatology. While IVT is widely used for studying water vapor fluxes and atmospheric rivers, this study also illuminates the need to understand the variability in moisture content obscured by the IVT variable.