Assessing the impacts of hydrodynamic parameter uncertainties on simulated evapotranspiration in a mountainous watershed

•We use a global sensitivity analysis to assess the sensitivity of evapotranspiration to the hydrodynamic parameters.•Hydrodynamic parameter uncertainties lead to 20% to 50% uncertainties in simulated evapotranspiration.•Evapotranspiration is sensitive to the permeability in grasslands and the Van Genutchen parameters in forests. Accurate quantification of the evolution of water resources requires a better understanding of the movements of water and energy from the subsurface to the lower atmosphere; physically-based integrated hydrologic models provide one of the key approaches to build such understanding. However, these models utilize a significant number of parameters that are measured only sparsely if at all—in particular, the hydrodynamic parameters. In this work, we perform a global sensitivity analysis to quantify the sensitivity of evapotranspiration (ET) to the hydrodynamic parameters. We study the East River watershed located in the Coloradobasinand characterized by cold and snowy winters and hot summers, high topographic gradients, and heterogeneous land cover and geology. Our results highlight that hydrodynamic parameter uncertainties lead to 20% to 50% uncertainties in ET.In areas characterized by a disconnection betweengroundwaterand land surface processes (under water-limited conditions),hydrodynamic parameter uncertainties strongly impactETwhich is highly sensitive to the parameters describing the unsaturated zone parameters. Conversely, in energy-limited areas where plants have year-round access to groundwater,ETis mainly sensitive to the effects of saturated hydraulic conductivities. ET uncertainties due to the uncertainties in hydrodynamic parameters were higher than those associated with the river stages and water table depths. Therefore,ETmeasurements could be used to improve the estimation of hydrodynamic parameters.