The EPA’s National Stormwater Calculator (SWC), which can help site developers and landscape architects reduce runoff from a property, has been updated. The SWC estimates the annual amount of rainwater and frequency of runoff from a specific site anywhere in the United States (including Puerto Rico). The calculator bases its estimates on local soil conditions, land cover and historic rainfall records.
The water management calculator accesses several national databases that provide soil, topography, rainfall, and evaporation information for the chosen site. The user supplies information about the site’s land cover and selects the types of low impact development (LID) controls they would like to use.
This update to the SWC will allow users to consider how runoff may vary based on historical weather and potential future climate. To better inform decisions, it is recommended that the user develop a range of SWC results with various assumptions about model inputs such as percent of impervious surface, soil type, sizing of green infrastructure, as well as historical weather and future climate change scenarios.