National Stormwater Calculator

Posted on: 7/31/2017 - Updated on: 2/27/2020

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The EPA Stormwater Calculator (SWC) is a desktop tool that can be used by individuals looking to reduce stormwater runoff at the local level. The SWC generates rainfall runoff volume and frequency estimates for any location in the United States or Puerto Rico using historic rainfall data, local soil properties, and land use cover inputs. Users can manipulate the land use category and evaluate how seven different green infrastructure methods can alter runoff volume and frequency on their property. This tool also has a specific climate change function that allows users to better understand how climatic variability and land use practices interact to affect stormwater runoff at local scales, which can inform future planning, policy, management, and implementation work in a variety of sectors, helping to mitigate flood risk and improve water quality.

Example in use: Students applied the National Stormwater Calculator to minimize stormwater runoff and create a resilient site design for a new community library in Mount Washington, Kentucky. Comparing original design plans with an updated plan that includes low-impact development (LID) components including cisterns, bioswales, and raingardens, the students demonstrated that green infrastructure solutions could help mitigate five inches of stormwater runoff from the library site annually, as well as almost completely eliminate water needs at the facility itself. In addition, the students demonstrated that the LID components would help the site accommodate potential increases in precipitation as a result of climatic variability, minimizing flood risk for both the site and the larger community.

Phase of Adaptation: Assessment, Planning


Land managers, water utility managers, local authorities, planners, policymakers, engineers, public


U.S. Environmental Protection Agency

Managing Organizations

The Environmental Protection Agency is an independent executive agency of the United States federal government tasked with environmental protection matters. The Environmental Protection Agency has ten Regional offices, each of which is responsible for the execution of the Agency's programs within several states and territories.