Hydroclimatic Variability of the Northeast United States

Over the historical record, the climate of the Northeastern United States (hereafter Northeast) has moved in and out of periods of drought and pluvial conditions. Precipitation has increased drastically over the past three decades but, within the same time frame, the Northeast has also experienced several significant drought events. If we can more fully understand the processes and drivers behind extreme hydroclimatic events in the historical record we may be able to gain a better understanding of the dynamics of why things are changing, aiding not only in our interpretation of global climate models but in the processes themselves. A multi-scale (regional-to-local), meteorological analysis of heavy precipitation events and an in-depth analysis on the meteorological drivers of soil moisture variability in the Northeast allows for the analysis and quantification of the various feedbacks between scales and the atmosphere and land surface.

First, I compare daily precipitation accumulations from the ERA5 Global Reanalysis (hereafter ERA5) and the US Global Historical Climate Network (hereafter GHCN) across the Northeast to evaluate the use of precipitation from ERA5 in applications across the Northeast. I find that the distance from the Atlantic Coast, elevation difference between ERA5 estimates and GHCN observations, and seasonality affect precipitation relationships between the two datasets. Then, I used a multi-duration (1, 2, 3, 7, 14, and 30 days), multi-return interval (2, 5, 10, and 50 years) observational precipitation dataset to diagnose changes in, and synoptic patterns associated with the identified precipitation events across the Northeast from 1895 to 2017. I found increasing trends in all duration and return-interval event combinations and that the rarest, longest duration events are increasing at faster rates than more frequent, shorter duration events. Additionally, daily synoptic patterns associated with events are similar across all durations and return-intervals and include coastal low, deep trough, east coast trough, zonal, and high pressure patterns. Finally, I sought to assess the meteorological drivers in soil moisture variability over the growing season at in-situ soil moisture observing sites across the Northeast. I found that seasonality and geographic location of stations lead to differences in the importance of meteorological drivers on surface soil moisture observations. This dissertation identifies useful tools for the estimation of precipitation across the Northeast, expands knowledge on trends and synoptic patterns associated with a spectrum of impactful precipitation events, and introduces new methods for the analysis of the meteorological drivers of soil moisture variability over the growing season.