If you’ve ever tried to model how a few hundred new oak trees might stop a local creek from flooding a basement, you’ve probably run into i-Tree. It’s the gold standard. But specifically, i-Tree Hydro Plus is a different beast entirely. It isn’t the breezy, web-based tool your cousin uses to check the value of the maple in their backyard. Honestly, it’s a rigorous, process-based powerhouse that demands specific inputs to function correctly.
Getting the data right is the hardest part. You can't just guess.
Most researchers and urban planners look for an i-Tree Hydro Plus data requirements infographic because the manual is, well, dense. It’s a lot of C++ backend talk and XML configuration. If you miss one parameter for soil conductivity or mess up your weather station's hourly timestamp, the whole simulation can go sideways. Here’s the reality of what actually goes into the model and why that "infographic" in your head needs to be organized by four major pillars.
The Topography Pillar: More Than Just "Hills"
You might think a basic map is enough. It isn’t. Hydro Plus relies on a Topographic Index (TI). This isn't just a "pretty" elevation map; it’s a statistical distribution of how water moves across the land.
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Basically, the model divides your watershed into "bins" based on the likelihood of saturation. To get this right, you usually need a Digital Elevation Model (DEM). In the U.S., you've got it easy—the USGS provides these. If you're working internationally, you're looking at a much steeper climb. You have to process your own DEM to generate a TI file that tells the software exactly where the "dip" in the land is and where the water will pool first.
Land Cover: The "Plus" in the Equation
This is where the model earns its keep. Unlike older models that just used a simple "Curve Number," i-Tree Hydro Plus wants to know about the leaves. It needs the Leaf Area Index (LAI) and the percentage of evergreen vs. deciduous canopy.
Why? Because a pine tree in winter handles a rainstorm differently than a bare maple.
You’ll also need to define the "Directly Connected Impervious Area" (DCIA). This is a big one. It's not just "how much pavement is there?" It's "how much of that pavement drains directly into a pipe or a stream without hitting a patch of grass first?" If you overestimate this, your peak flows in the model will look like a tsunami.
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What You'll Actually Need to Input:
- Tree Canopy %: The total overhead coverage.
- Shrub Cover %: Often overlooked but vital for understory interception.
- Herbaceous/Short Vegetation %: Your lawns and fields.
- Impervious Surface %: Roads, roofs, and parking lots.
- Water %: Open ponds or rivers within the domain.
Weather and Climate: The Hourly Grind
Hydro Plus doesn't do "daily averages." It lives and breathes hourly data. If you're using the WeatherPrep utility—which you probably should—it’s going to look for NOAA Integrated Surface Database (ISD) formats.
You need precipitation, temperature, wind speed, and solar radiation.
If you have a gap of even three hours in your weather file, the simulation might crash or, worse, give you "ghost data" where the soil moisture calculations drift into nonsense. For those in snowy climates, the model now includes cold climate routines. That means you also need to account for snow interception and melt rates. It's not just "rain in, runoff out" anymore; it's a complex energy budget.
The Calibration Catch-22
Technically, you can run Hydro Plus with "defaults." Don't do that.
To get "human-quality" results that actually stand up in a city council meeting, you need stream gauge data. This is for the auto-calibration tool. You feed the model real-world flow data from a nearby USGS gauge, and it runs hundreds of iterations to find the perfect soil parameters—like hydraulic conductivity and "m" (the scaling parameter for subsurface flow).
Without this, you're just playing a very expensive version of SimCity.
Actionable Next Steps for Your Project
If you are staring at a blank project screen right now, stop. Don't start clicking buttons yet.
First, head over to the i-Tree Research Suite and grab the latest HydroPlus Technical Manual. It’s the "bible" for this specific version. Second, use i-Tree Canopy to get your land cover percentages—it’s a much faster way to sample your area than trying to manually digitize a whole city from satellite imagery.
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Once you have your percentages, download the WeatherPrep tool. Try to find a weather station with at least 95% data coverage for your target year. If you can't find a local station with hourly records, you might have to interpolate from a secondary site, but be careful—mountains and coastlines make "nearby" data very unreliable.
Finally, ensure your XML config file is formatted correctly. One missing bracket in that file is usually why the model fails to launch. Check your file paths twice. If you're on Linux, remember that file paths are case-sensitive, which trips up a lot of Windows-based researchers.
Gather your DEM, grab your hourly weather, and define your tree species. That’s how you move from a pretty infographic to a model that actually predicts the future of your watershed.