Water Resources Research Act Program

Principal Investigators: M. Todd Walter

Abstract: Riverine flooding within Hudson River Basin communities is often derived from extreme precipitation occurring over the largely forested catchments. 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. Hydrological land surface models for prediction of flooding extremes over- generalize plant dynamics, often utilizing taxonomic classifications (e.g. coniferous vs. deciduous) rather than a more hydrologically relevant clustering by functional traits that govern plant hydraulic regulation. In the Northeastern US, warming air temperatures have engendered a decline of Eastern Hemlock (Tsuga canadensis), and subsequent increases in observed catchment water yield. Previous stable water isotope analysis of Eastern Hemlock and American Beech (Fagus grandifolia; a candidate successional species) plant xylem shows evidence of greater groundwater uptake in Eastern Hemlock than American Beech during both wet and dry seasons, possibly suggesting Eastern Hemlock provides an important control on catchment storage and surface runoff. We propose to continuously measure sapflux of Eastern Hemlock and candidate successional species and shallow soil water content throughout one growing season. We will perform isotopic analysis (2H and 18O) of soils and tree xylem twice during the growing season. We will apply these observations to a plot-scale ecohydrological model to understand how Eastern Hemlock and successional species modulates the depth of soil water uptake, providing an important control on groundwater and near-stream runoff. Results from this research will be used to parameterize a regional hydrologic land surface model to understand how a loss of Eastern Hemlock could impact flooding across New York State.