Importance of parameter and climate data uncertainty for future changes in boreal hydrology

Authors: MARSHALL, ADRIENNE - University Of Idaho; LINK, TIMOTHY - University Of Idaho; Flerchinger, Gerald; LUCASH, MELISSA - University Of Oregon

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2021
Publication Date: 8/4/2021
Citation: Marshall, A.M., Link, T.E., Flerchinger, G.N., Lucash, M.S. 2021. Importance of parameter and climate data uncertainty for future changes in boreal hydrology. Water Resources Research. 57(8). Article e2021WR029911. https://doi.org/10.1029/2021WR029911.
DOI: https://doi.org/10.1029/2021WR029911

Interpretive Summary: Boreal forests in northern latitudes are changing rapidly with permafrost deterioration, changes in forest composition, and rapid changes in hydrology in the wake of permafrost thaw. Future trends in evapotranspiration and soil water content will have a large influence on hydrologic changes but are quite uncertain. This study conducted a sensitivity analysis using a physically-based ecohydrologic model in multiple boreal forest types to assess the influence of model parameters and future climate scenarios on evapotranspiration and soil water content. Best estimates and uncertainty of these plant and soil parameters are provided. However, future scenario simulations of evapotranspiration and soil water content were as sensitive to the choice of parameter values and global climate model (GCM) as much as projected effects of climate change in a late-century. This assessment of the most important parameters and direction of their effects can provide guidance to modelers and consumers of modeling studies who want to understand how sensitivity of parameter values affect predicted of climate change impacts on hydrology in boreal regions.

Technical Abstract: Soil moisture and evapotranspiration (ET) are important components of boreal forest hydrology that affect ecological processes and land-atmosphere feedbacks. Future trends in soil moisture in particular are uncertain, therefore accurate modeling of these fluxes and understanding of concomitant sources of uncertainty are critical. Here, we conduct a global sensitivity analysis, Monte Carlo parameterization, and analysis of parameter uncertainty and its contributions to future soil moisture and ET uncertainty using a physically-based ecohydrologic model in multiple boreal forest types. Soil and plant hydraulic parameters and LAI have the largest effects on summer soil moisture at two contrasting sites. We report best estimates and uncertainty of these parameters via a multi-site Generalized Likelihood Uncertainty Estimation approach. In future scenario simulations, parameter and global climate model (GCM) choice influence projected changes in soil moisture and evapotranspiration as much as the projected effects of climate change in a late-century, high-emissions scenario, though the relative effect of parameters, GCM, and climate vary between objective and study site. Saturated water content, as well as the sensitivity of stomatal conductance to vapor pressure deficit, have the most statistically significant effects on change in evapotranspiration and soil moisture, though there is considerable variability between sites and GCMs. In concert, the results of this study provide estimates of: (1) parameter importance and statistical significance for soil moisture modeling, (2) parameter values for physically-based soil-vegetation-atmosphere transfer models in multiple boreal forest types, and (3) the contributions of uncertainty in these parameters to soil moisture and evapotranspiration uncertainty in future climates.