Ecohydrological decoupling under changing disturbances and climate

Authors: MCDOWELL, N.D. - Pacific Northwest National Laboratory; ANDERSON-TEIXEIRA, K. - Smithsonian Institute; Biederman, Joel; BRESHEARS, D.D. - University Of Arizona; FANG, Y. - Pacific Northwest National Laboratory; FERNANDEZ-DE-UNA, L. - Centre For Ecological Research And Forestry Applications (CREAF); GRAHAM, E.B. - Pacific Northwest National Laboratory; MACKAY, D.S. - University Of Buffalo; MCDONNELL, J.J. - University Of Saskatchewan; MOORE, G - Georgia Southern University; NEHEMY, M.F. - University Of Saskatchewan; STEVENS RUMANN, C - Colorado State University; STEGEN, J. - Pacific Northwest National Laboratory; TAGUE, N. - University Of California; TURNER, M.G. - University Of Wisconsin; 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. https://doi.org/10.1016/j.oneear.2023.02.007.
DOI: https://doi.org/10.1016/j.oneear.2023.02.007

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.