Insights on geologic and vegetative controls over hydrologic behavior of a large complex basin – Global Sensitivity Analysis of an integrated parallel hydrologic model Vibhava Srivastava a,⇑ , Wendy Graham a , Rafael Muñoz-Carpena b , Reed M. Maxwell c a Water Institute, University of Florida, 570 Weil Hall, PO Box 116601, Gainesville, FL 32611-6601, USA b Department of Agricultural and Biological Engineering, University of Florida, 287 Frazier Rogers Hall, PO Box 110570, Gainesville, FL 32611-0570, USA c Department of Geology and Geological Engineering, Colorado School of Mines, 1500 Illinois Street, Golden, CO 8040, USA article info Article history: Received 23 April 2014 Received in revised form 4 October 2014 Accepted 7 October 2014 Available online 16 October 2014 This manuscript was handled by Corrado Corradini, Editor-in-Chief, with the assistance of Masaki Hayashi, Associate Editor Keywords: Integrated hydrologic modelling Global Sensitivity Analysis Groundwater–surface water interactions Coupled hydrologic processes summary This study demonstrated the first application of a GSA technique to a transient ISSHM–LSM application developed for a large-scale river basin. The Morris method was used to identify the spatially and tempo- rally variable sensitivity amongst a large number of model parameters to provide insights on hydrologic processes dominating behavior in the basin and to identify a small subset of parameters that should be evaluated in subsequent, more computationally intensive quantitative GSA and parameter estimation techniques. Results showed that in the upper region of the basin, evapotranspiration (ET), total stream- flow and peak streamflow were less sensitive to surficial aquifer system characteristics, but highly sen- sitive to the hydraulic conductivity of the confining unit separating the surficial aquifer and the regional aquifer system and leaf area index of near stream vegetation. In the lower region of the basin, hydraulic conductivity of the regional aquifer system was found to have a significant effect on ET, total stream flow, and groundwater contributions to streamflow while surface–groundwater dynamics during storm events was most sensitive to storage properties of the regional aquifer system. Peak streamflow in the lower basin was most sensitive to the hydraulic conductivity of the confining unit in the upper basin, and the Manning’s coefficient of upper basin streams, indicating that all peak storm flows originate in the upper basin. Throughout the basin ET was sensitive to soil/geologic properties and vegetation properties, with unsaturated zone processes and relevant parameters gaining importance in moisture limited condi- tions existing in the lower regions of the basin. Published by Elsevier B.V. 1. Introduction Although the first blueprint for an integrated hydrologic model was outlined by Freeze and Harlan (1969), it was not until recently that significant advances were made in the development of robust, Integrated, Surface–Subsurface Hydrologic Models (ISSHMs) that exploit advanced parallel computational capabilities and represent the surface–subsurface-near land surface hydrologic processes in an integrated and physically plausible manner (e.g. ParFlow, Ashby and Falgout, 1996; Kollet and Maxwell, 2006, 2008a; InHm, VanderKwaak, 1999; MODHMS, Panday and Huyakorm, 2004; HydroGeoSphere, Therrien et al., 2005). In general, spatially- distributed, coupled models simplify how surface and subsurface flow equations are solved and the information is exchanged between the two modeled domains (i.e. surface and subsurface), whereas spatially-distributed integrated models simultaneously solve the equations for the two flow systems (i.e. surface and subsurface) in a mass conservative fashion (see more details on coupled versus integrated models in Condon and Maxwell, 2013; Maxwell et al., 2014). Although this may be a small conceptual distinction, it comes at a very high computational cost (Condon and Maxwell, 2013). The high computational cost associated with the integrated representation of a three-dimensional, variably saturated surface– subsurface environment has limited the application of ISSHMs pri- marily to idealized hillslopes or homogenized small catchments (area 10 0 –10 1 km 2 , e.g. Ebel et al., 2008;Jones et al., 2008; Sudicky et al., 2008; VanderKwaak and Loague, 2001). A few appli- cations of ISSHMs have involved a simulation of the hydrologic behavior of medium-scale watersheds (area 10 2 km 2 , e.g. Condon and Maxwell, 2013; Condon and Maxwell, 2014a, 2014b; Ferguson and Maxwell, 2010; Kollet and Maxwell, 2008b; Li http://dx.doi.org/10.1016/j.jhydrol.2014.10.020 0022-1694/Published by Elsevier B.V. ⇑ Corresponding author. Tel.: +1 352 392 5893; fax: +1 352 392 6855. E-mail addresses: vibhava@ufl.edu (V. Srivastava), wgraham@ufl.edu (W. Graham), carpena@ufl.edu (R. Muñoz-Carpena), rmaxwell@mines.edu (R.M. Maxwell). Journal of Hydrology 519 (2014) 2238–2257 Contents lists available at ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol