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- Title
Possible Increases in Flood Frequency Due to the Loss of Eastern Hemlock in the Northeastern United States: Observational Insights and Predicted Impacts.
- Authors
Knighton, James; Conneely, Justin; Walter, M. Todd
- Abstract
Trees exert a fundamental control on the hydrologic cycle, yet previous research is unclear about the nuanced relationship between forest cover and riverine flood frequency. In the Northeastern United States, warming air temperatures have resulted in a decline of Eastern Hemlock (EH), and subsequent increases in observed catchment water yield. We evaluated the possibility of EH loss leading to a changed flooding regime. We first investigated plant hydraulic regulation by root water uptake in EH and American Beech (AB; a candidate successional species) through stable isotope analysis of stream, soil water, and plant xylem water. EH xylem water showed evidence of deeper soil water uptake than AB during both wet and dry seasons, suggesting species succession may be an important mechanism for altering catchment "plant accessible water." Next, we estimated catchment flood frequency with mechanistic hydrologic simulations for present conditions, and two hypothetical cases where all EH is succeeded by AB. The largest change to catchment extreme discharge after AB succession coincided with fall season tropical moisture export‐derived precipitation. We observed reduced sensitivity under future climatic forcing with an ensemble simulation of five localized constructed analogs downscaled general circulation models. Thus, the influence of forest composition on the flood regime may be most related to the temporal alignment of the synoptic‐scale processes that generate Atlantic Basin tropical cyclones and regional plant phenology of the Northeast United States. Our results provide a justification for using physically based hydrologic models incorporating plant hydraulic regulation when evaluating future flooding frequency. Key Points: We evaluate the possibility of climate‐induced changes in forest cover leading to shifts in the catchment flood frequency distributionWe demonstrate differences in root uptake hydraulic regulation of transpiration between Eastern Hemlock and American BeechThe influence of forest composition on the flooding is sensitive to the temporal alignment of tropical cyclones and tree phenology of the Northeast United States
- Subjects
UNITED States; PLANT phenology; GENERAL circulation model; PLANT-water relationships; HYDROLOGIC cycle; STABLE isotope analysis; TROPICAL cyclones; FLOODS; WATERSHEDS
- Publication
Water Resources Research, 2019, Vol 55, Issue 7, p5342
- ISSN
0043-1397
- Publication type
Article
- DOI
10.1029/2018WR024395