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Research Project: Understanding Water-Driven Ecohydrologic and Erosion Processes in the Semiarid Southwest to Improve Watershed Management

Location: Southwest Watershed Research Center

Title: Ecohydrological decoupling under changing disturbances and climate

item MCDOWELL, N.D. - Pacific Northwest National Laboratory
item ANDERSON-TEIXEIRA, K. - Smithsonian Institute
item Biederman, Joel
item BRESHEARS, D.D. - University Of Arizona
item FANG, Y. - Pacific Northwest National Laboratory
item FERNANDEZ-DE-UNA, L. - Centre For Ecological Research And Forestry Applications (CREAF)
item GRAHAM, E.B. - Pacific Northwest National Laboratory
item MACKAY, D.S. - University Of Buffalo
item MCDONNELL, J.J. - University Of Saskatchewan
item MOORE, G - Georgia Southern University
item NEHEMY, M.F. - University Of Saskatchewan
item STEVENS RUMANN, C - Colorado State University
item STEGEN, J. - Pacific Northwest National Laboratory
item TAGUE, N. - University Of California
item TURNER, M.G. - University Of Wisconsin
item CHEN, X.Y. - Pacific Northwest National Laboratory

Submitted to: One Earth
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2022
Publication Date: 3/17/2023
Citation: Mcdowell, N., Anderson-Teixeira, K., Biederman, J.A., Breshears, D., Fang, Y., Fernandez-De-Una, L., Graham, E., Mackay, D., Mcdonnell, J., Moore, G., Nehemy, M., Stevens Rumann, C.S., Stegen, J., Tague, N., Turner, M., Chen, X. 2023. Ecohydrological decoupling under changing disturbances and climate. One Earth. 6(3):251-266.

Interpretive Summary: Forests are increasingly impacted by drought, wildfire, and insect infestation, all of which are accelerating with climate change. Forests die-off often changes the hydrologic cycle with consequences for the post-disturbance vegetation, streamflow, and groundwater. In some places, forest die off generally increases streamflow, while drying effects are more commonly reported in drier years and drier regions. Here we review the literature on interactions between forest die-off and the water cycle. We develop a framework for understanding different hydrologic responses in different watersheds based on the degree to which streamflow generation and plant root water uptake rely on the same pools of soil water. We provide a framework of testable hypotheses as a roadmap for future work in disturbance hydrology research.

Technical Abstract: Terrestrial disturbances are increasing in frequency and severity, perturbing the hydrologic cycle by altering vegetation-mediated water use and microclimate. These hydrologic changes feed back on vegetation succession, which is additionally influenced by changing climate and atmospheric CO2. The complexity of these interacting drivers and feedbacks causes uncertainty regarding the sustainable provision of freshwater through streamflow. Here we synthesize the literature on post-disturbance ecohydrological coupling, i.e. the bi-directional relationship between vegetation succession and streamflow, under changing disturbance regimes, CO2 concentrations, and climate. Disturbance can cause decoupling through altering the size, availability, and location of the source water pools for transpiration and streamflow. Decoupling increases when soil moisture is low due to reduced overlap in these pools. Successional trajectories regulate the physiological and physical features influencing the dynamics of source water interaction. Changing disturbance and climate regimes can slow succession, alter its trajectory, and prolong decoupling, with potential moderation by CO2. Increasing rates, severity, and spread of disturbances along with warming could promote greater decoupling globally. A testable hypothesis framework emerged that provides a roadmap for future research. Accurate prediction of post-disturbance ecohydrologic coupling requires understanding the controls regulating the overlap between source water pools for transpiration and streamflow, and their response to succession under changing disturbance and climate regimes.