United States Environmental Protection Agency
The National Stormwater Calculator (SWC) estimates runoff at a site based on available information such as soil type, landscape and land-use information, and weather. In 2013 EPA released an updated verision of this calculator. 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.