i-Tree Hydro+

April 14, 2021

(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 containing:
    • i-Tree Hydro: a statistically-distributed 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 the Hydro GUI and Hydro+ being synchronized at Hydro version 6.3 and HydroPlus code revisions 377-582.
    • 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+. The Hydro GUI User Manual is also linked to below for reference, while it is being merged into the Hydro+ Technical Manual.
  • 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 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 (the predecessor to the latest HydroPlus.exe), which is used in the i-Tree Hydro v6 GUI. The latest in-development version of HydroPlus is also available, 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 HydroPlus 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) HydroPlusConfig.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. HydroPlus 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

  • Latest HydroPlus package (revision 701) including model .exe, manual, test cases and auto-testing script (C++, .zip). Note that this includes code to simulate green infrastructure, but those features are still in development and prone to significant changes. No technical support is available for the latest Hydro+ package at this time.

  • Weather preprocessor scripts and utility (revision 5) based on Hirabayashi & Endreny, 2016 (C#, .zip)
    • Warning for first-time users: If running WeatherDataExtractor.exe generates an error about Microsoft.ACE.OLEDB.12.0, in the WeatherDataExtractor.sln search all instances of “Microsoft.ACE.OLEDB.12.0” and replace with “Microsoft.Jet.OLEDB.4.0”.
    • LocationSpecies.MDB is no longer included in i-Tree since Suite Version 6.1.36 (released Feb 24, 2021). A copy of LocationSpecies.MDB from i-Tree Suite Version 6.1.35 is available at this link for use with the standalone weather preprocessor, until an update is released linking the preprocessor to the online version of the database: http://bit.ly/LocationSpeciesV6-1-35
  • Autocalibration utilities for Hydro+ (revision 2) derived from PEST 17.1 (.zip)


Video Learning

Scientific papers describing Hydro+ model methods