i-Tree Hydro+

Nov. 17, 2020

(If you have questions about this tool, please contact both Dr. Ted Endreny <te@esf.edu> and i-Tree support <info@itreetools.org>. Note that free technical support is not available for Research Suite tools including Hydro+. Email i-Tree support about consultation.)

Summary of Hydro+ features

  • i-Tree Hydro+ is a suite of process-based environmental models that share common algorithms, organized in a C++ solution called "UnifiedHydro", containing:
    • i-Tree Hydro: a hydrology model simulating the effects of land cover changes on water quantity and quality, unique in explicitly modeling vegetation processes (Wang et al., 2008). This is the model used by the i-Tree Hydro graphical user interface (GUI) included in the i-Tree Suite, with Hydro+ and Hydro being synchronized at Hydro version 6.3 and UnifiedHydro revision 377.
    • i-Tree Cool Air: a spatially-explicit air temperature model simulating the effects of land cover changes using i-Tree Hydro's water budget and an energy budget that explicitly accounts for vegetation processes (Yang et al., 2013).
    • i-Tree Cool River: a river temperature model for simulating the effects of channel morphology, riparian shading, tributaries, stormwater inflow, groundwater mixing, and river restoration by using a set of 1D advection, dispersion, and energy flux equations (Abdi & Endreny, 2019).
  • A Weather Preprocessor utility derived from i-Tree Eco is available to prepare inputs for Hydro+ models.
  • Test Cases serve as sample input-output for all Hydro+ models and simulation modes.
  • A Technical Manual serves as a central source of guidance about use and development of Hydro+.
  • No free technical support is available for the i-Tree Research Suite; to inquire about consultation for these models, contact i-Tree support.


The Hydro+ environmental model suite – called UnifiedHydro in reference to its C++ codebase – includes the process-based models i-Tree Hydro, i-Tree Cool Air, and in the future potentially other models developed by the iTree-ESF collaborative. These models share common algorithms (for example, to simulate interception by tree canopy) and are thus 'unified' in Hydro+. The Hydro+ code is continually being developed. Below you can find a stable version of UnifiedHydro.exe, used in the i-Tree Hydro v6 GUI, and a latest in-development version of it, including green infrastructure and other model and code improvements.

The Hydro+ Technical Manual includes some history to provide context and institutional knowledge. This document serves as an FAQ for the researchers developing and using Hydro+. The Technical Manual is evolving and expanding over time to include basic information about code architecture and common development practices (e.g. how to add new functions and inputs); explanation and solutions to common problems that come up when working with these complex models; and different options or configurations possible for running these programs.

This page offers the UnifiedHydro C++ source code and a compiled executable file for running the code. The model executable is run from the command line along with an extensible markup language (XML) UnifiedHydroConfig.xml file, which includes model settings and parameters. See the Technical Manual for information on how to interact with the source code or use the compiled executable file. UnifiedHydro C++ can be edited and recompiled with Visual Studio 2019 Community Edition (or VS2017 for the stable Hydro v6.3 code), which is freeware. A weather preprocessor is also available below, based on an i-Tree Eco batch weather preprocessing utility, which can format raw hourly weather archives from NOAA's Integrated Surface Database and preprocess that formatted raw data (as described in Hirabayashi & Endreny, 2016) for use in the Hydro and Cool Air models.

Being part of the i-Tree Research Suite of advanced tools, i-Tree's usual level of technical support and documentation is not available for Hydro+. This tool is intended for users with a moderate level of expertise in environmental and computer science. Technical support is not available for free, but expert consultation can be arranged. If interested in consultation, reach out to the i-Tree Team at info@itreetools.org.


Hydro+ Package

Code, utilities, inputs and outputs


Video Learning

Scientific papers describing Hydro+ model methods