How to Use i-Tree GHG
i-Tree GHG estimates the benefits of tree-planting projects over the project lifetime. The focus is on greenhouse gases (GHG), but all ecosystem services are included.
Interested in viewing this How-To text while you work on your Species project? Click on the Menu drop-down list in the navigation bar at the top of the page, then right-click Help and click Open Link in New Window. This will open the How-To text in a separate window so you can conveniently view both webpages at once.
Successfully creating a project in i-Tree GHG is easy! Simply work left to right through the tabs, providing the required data as you go. (To move between tabs, click the Next button or click on the desired tab itself.)
1. Location ¶
On the “Location” tab, identify the geographic location of your study area, beginning with the state and continuing through the fields. Location information is used to determine available species, tree growth rates, energy conservation, stormwater conservation, and air quality improvements.
If your project spans nearby cities, it is reasonable to simply enter the city that lies near the center of the project. If, however, your project includes cities that are widely separated and that have different climates, species, and air pollution conditions, it is better to run i-Tree GHG separately for each general region.
The project “Parameters” tab allows you to enter data specific to the overall project.
Electricity Emissions Factor ¶
An electricity emissions factor represents the amount of greenhouse gases emitted for every unit of electricity produced at the power plant. It is related to the fuel used in your region to produce energy. Coal, for example, has a high electricity emissions factor, i.e., burning coal to produce electricity emits a lot of greenhouse gases. Hydroelectric power, wind, solar, and nuclear power, in contrast, produce almost no greenhouse gases. The electricity emissions factor varies from power plant to power plant and even from day to day, based on the mix of fuel types.
There are a number of sources for this information.
- It may be specified by a project sponsor.
- You can contact your electricity provider or search their documentation online.
- Data at a variety of scales (region, state, power plant) can be gathered from the US EPA's eGRID database.
- State averages can be found at the US EIA. To find your state's average, click on the state name in the Table. You'll find the value under Emissions, Carbon dioxide (lbs/MWh).
Enter the value in the Electricity Emissions Factor box and be sure to indicate the correct units. (You'll want to double check both the sides of the units. The value you find may be reported as pounds or kilograms and per kWh or MWh.)
Fuel Emissions Factor ¶
This value represents the greenhouse gas emissions associated with heating fuels. In contrast to the electricity emissions factors, these don't vary by region but rather according to the specific fuel used for heating (natural gas, propane, electricity). The fuel emissions factors also don't vary over time. Every unit of natural gas, for example, burned for heat anywhere in the world and at any time pretty much emits the same amount of greenhouse gases.
Technically, the heating fuel and thus the fuel emissions factor can vary from building to building. Adjusting this for every building impacted by your project, however, would be prohibitively difficult. Instead, we recommend using the fuel emissions factor for the heating source that is most common in your region. Some common values include:
- Natural gas: 53.1 kg/MMBtu
- Propane: 63.1 kg/MMBtu
- Wood: 94.1 kg/MMBtu
- Heating oil: 73.16 kg/MMBtu
- If your region primarily uses electricity for heat, you can convert the electricity emissions factor you entered above into a fuel emissions factor by dividing it by 3.41 to yield lbs/MMBtu or kg/MMBtu.
Years for the Project ¶
i-Tree GHG will project the benefits for up to 99 years into the future. Enter the number of project years here.
Tree Mortality over Project Lifetime ¶
i-Tree GHG will incorporate mortality into the projected benefits. If you have an estimate of the mortality you expect over your project's lifetime, you can enter it here. If you prefer to calculate the benefits without accounting for mortality, enter 0.
3. Trees ¶
The GHG and energy conservation benefits of a project depend on a variety of factors, including tree species and size, distance and direction to the nearest building, characteristics of that building, and details of the trees planted. Under the Trees tab, you will enter each unique configuration of these elements and the number of trees that feature those particular elements.
Tree Information ¶
- Using the drop-down menu, indicate the species of one of the configurations of trees to be planted. You can toggle between scientific and common names with the buttons at the top. If your species is not available, choose the most closely related species (consider family relationships, growing form, mature size). If that is not feasible, you can choose the most appropriate of the "Other" categories of trees.
- Enter the
DBHat the time of the project start. In most cases, this is the DBHat planting.
Building Information ¶
- Distance to Nearest
- For trees that will be planted to shade buildings, enter the distance class to the nearest building (0-19 ft, 20-39 ft, 40-59 ft, > 60 ft). Note that this could be a building on an adjacent site. For trees more than 60 ft away, no shade benefits will be calculated.
- Tree is to _____ of Building
- Enter the direction the tree lies with respect to the building. For trees more than 60 ft away, this field can be ignored.
- The age of the building to be shaded affects its energy efficiency and therefore the potential benefits the trees can bring. If you know this information, choose the vintage class from the drop-down menu. Alternatively, you can consider the typical age of buildings for the area where you are working. For trees more than 60 ft away, this field can be ignored.
- Climate Controls
- Trees can only have an impact on
energy use in buildings where energy is used to heat or cool. If you know whether the
buildings to be shaded have
A/Cor heat, choose the appropriate item from the drop-down menu. Alternatively, choose the option that is most common for the area where you are working. For trees more than 60 ft away, this field can be ignored.
Tree Details ¶
- The condition of the trees will affect how well they grow and thus future benefits. Enter the appropriate condition of the trees here. For new plantings, this will likely be "Excellent."
- Exposure to Sunlight
- The exposure to sunlight affects both how the trees grow and the degree to which a new tree adds shade to a building. Enter the appropriate exposure to sunlight here. For new trees, this will likely be "Full sun."
- Number of Trees
- Enter the number of trees with this configuration, i.e., this combination of species, DBH, distance and direction to nearest building, etc.
- Additional configurations
- To add a new configuration, click the "+" button on the left. A new row will be added where the above data can be entered for the new group of trees.
4. Report ¶
The results are presented under the “Report” tab. The project summary is shown at the top. Each configuration that you entered on the Trees tab is shown as its own row, with a summary of the characteristics to identify the group. Benefits summed for the project lifetime are shown under four green tabs above the table:
- CO2 Benefits
- The CO2 sequestered by the trees over the project lifetime is shown together with the CO2 benefits from reduced energy use.
- The benefits associated with reduced energy use for cooling and heating are shown. Note that some tree placements can result in higher energy use for heating when trees block the warming rays of the winter sun. In these cases, the benefits are shown with a negative sign.
- Stormwater benefits and total tree biomass are presented here. Stormwater benefits are presented in two ways. Rainfall interception indicates the annual amount of water captured by the trees' leaves over the course of a rainfall year (2010). Stormwater managed represents a new refinement to our modeling of the hydrological benefits of trees. It incorporates local rainfall data and county-level data on land cover (in particular, amounts of pervious vs impervious surface) to arrive at a more accurate representation of how much rainfall runoff, annually, is diverted from stormwater systems for a tree-planting project.
- Air pollution
- Air pollutants captured by the trees and air pollutants reduced owing to reduced energy use are shown here for four pollutants: O3, NO2, SO2, and small particulate matter.
Results can be viewed in English or metric units by toggling between the buttons above the table. The blue buttons immediately above the table allow you to copy the rows into your clipboard, download them as a .csv file, or save the project.