Green Infrastructure/Green Roofs

Elizabeth Farrell, CUNY Queens College; SUNY Nassau Community College


Runoff in urban areas is an increasingly important issue when it comes to water quality. It is a major hydrologic issue in New York City, as urban infrastructure creates excess runoff and impervious surfaces decrease the infiltration rate of land surfaces. This excess runoff, which often times carries with it pollutants and contaminants, has proven to create water quality issues. It has become ever more critical to try to mitigate the influx of runoff into our waterways. Urbanization increases runoff, and in NYC 64% of the area is impervious.

In this module students will explore green roofs as a potential solution to the environmental impacts of increased precipitation brought on by climate change. They will evaluate data collected from studies on 15 green roofs from different areas of the US and other countries, as well as historical precipitation data from Central Park in NY to illustrate how precipitation patterns are changing and if we need to use green infrastructure, such as green roofs, to combat the symptoms of climate change. Students will also use Model My Watershed , a watershed-modeling web app, to analyze real land use data, model storm-water runoff and water-quality impacts using professional-grade models, and compare how different conservation or development scenarios could modify runoff and water quality.

Strengths of Module

This module can give students an idea of what solutions are available to help address the problems caused by excess runoff. Students will address how green roofs impact environmental issues such as water quality, air quality, biodiversity and public health. The module promotes student learning by having students look at a large dataset of annual rainfall in Central Park, NY, and make their own decisions about how to edit down that data in order to evaluate how the rate of annual rainfall has been changing recently.

Students will have the opportunity to work with a user-friendly web app that uses professional-grade models to simulate hypothetical 24-hour storms and create their own plan for implementation of various types of green infrastructure. They will also use the model to see how rainfall intensity impacts percent runoff and to evaluate the effectiveness of different forms of green infrastructure on reducing the loading rate of total suspended solids, an indicator for water quality.

What does success look like

  • Discuss the importance of preserving water quality and identify some of the environmental problems associated with stormwater runoff
  • Analyze data and draw conclusions regarding current changes in precipitation patterns and usefulness of green infrastructure for water quality management
  • Evaluate and quantify the effectiveness of green infrastructure as a mitigation technique by using professional-grade models
  • Assess the additional benefits of green infrastructure
  • Use basic equations, shortcuts and graphing in Excel

Context for Use

This entire module can be completed in one three-hour lab period or two 90 minute lecture periods for introductory or intermediate level students. Activities A and B can be completed in a 90-minute class period, then instructors can demonstrate using Model My Watershed for Activity C and assign it as homework. Students also can work in pairs or groups to come up with their best plan for implementation of green infrastructure, which they would present to the class in the subsequent class period for a discussion of their findings.

This module has been used in a lab period for an environmental science course for non-majors, comprised primarily of freshmen, with green infrastructure being a topic of discussion in lecture. Instructors can also incorporate a green roof model activity where students simulate a rain storm and quantify the effectiveness of the green roof model for retaining rainfall and reducing runoff.

Description and Teaching Materials

See the teaching materials files, provided below, for a step-by-step description for carrying out this module. A student handout, describing Activities A, B, C, and instructor key are also provided.

Why this Matters:

As water supplies dwindle due to increased temperatures from climate change and increases in population, it is critical that society and the government properly manage our water resources. Water is a basic necessity for life and if steps are not taken to mitigate pollution and contamination that results from excess urban runoff, we will be paying the consequences for years to come.

Included in the teaching materials are a lab handout with background information, Excel sheets with data sets from a study summarizing the efficacy of green roofs from varying locations in the US and around the world, highest rainfall events in Central Park, annual rainfall in Central Park, NY, land use data for the Central Park subwatershed, and instructions on how to use Model My Watershed, as well as a PowerPoint presentation.

Quick outline/overview of the activities in this module

  • Activity A: Determine precipitation patterns and rates of change from modern datasets.
  • Activity B: Explore temporal distribution of intense rain events and wettest years to determine if rainfall intensity has changed over time.
  • Activity C: Evaluate data from green roofs to determine their effectiveness for reducing runoff. Use Model My Watershed to collect data using professional-grade models and implement their own green infrastructure plan.

Activity A

Students will download precipitation data for Central Park, NY, from 1869-2019, and create a graph to show precipitation patterns. By adding a trendline, they will be able to determine the overall rate of change by using linear regression.

Activity B

Students will download the highest precipitation events data and wettest years for Central Park, NY, from 1869-2019, and evaluate what the temporal distribution of intense rain events and wettest years has been. They will use this information to clip their graphs from Activity A in order to show how the rate of rainfall has changed in Central Park by using linear regression.

Activity C

Students will determine the range of the reduction in run off data from 15 different green roofs to see how effective green roofs are in decreasing the volume of water that becomes runoff. They will also consider other forms of green infrastructure and how NYC in particular plans to use these strategies to reduce runoff. Using Model My Watershed, they will analyze real land use data, model storm-water runoff and water-quality impacts using professional-grade models, and compare how implementation of different types of green infrastructure could potentially impact percent runoff during a rain event and the resulting loading rate of TSS as an indicator of water quality.

Workflow of this module:

  1. Assign any pre-class readings
  2. Give students their handout when they arrive to class
  3. Instructor gives brief PowerPoint presentation with background material. Discussion of the readings can be integrated into this presentation or done before.
  4. Students can then work through the module activities.

Teaching Materials:

  • Instructor's PowerPoint (PowerPoint 2007 (.pptx) 8.8MB Jul26 21)
  • Model My Watershed Completed Scenarios
  • Student Handout (Microsoft Word 2007 (.docx) 3.3MB Jul26 21)
  • Module Data (Excel 2007 (.xlsx) 27kB Jul26 21)

Teaching Notes and Tips

See the

and Instructor's PowerPoint (PowerPoint 2007 (.pptx) 8.8MB Jul26 21) for notes and tips for carrying out this exercise.

Measures of Student Success

Students should be able to effectively evaluate whether runoff is an issue that will need to be addressed as climate change impacts annual rainfall and frequency of intense rainfall events in New York City, and if green infrastructure could be used as a potential mitigation technique.

References and Resources

Berghage, R., D. Beattie, A. Jarrett, C. Thurig, F. Razaei, AND T. OCONNOR. Green Roofs for Stormwater Runoff Control. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/026, 2009.

Carson, T B, et al. "Hydrological Performance of Extensive Green Roofs in New York City: Observations and Multi-Year Modeling of Three Full-Scale Systems." Environmental Research Letters, vol. 8, no. 2, 1 June 2013, p. 024036, 10.1088/1748-9326/8/2/024036. Accessed 16 Sept. 2020.

NYC DEP 2010 NYC Green Insfrastructure Plan: a Sustainable Strategy for Clean Waterways