Future Precipitation Impacts on Stormwater Management

Future Precipitation Impacts on Stormwater Management

This tool is excerpted from Chesapeake Bay Watershed Climate Impacts Summary and Outlook for Spring 2021.

Tool Background

Global climate models provide projections of future precipitation conditions across the Mid-Atlantic that can serve as key inputs for stormwater management in the region. Other MARISA tools have examined these trends and made this data available, including changes in future seasonal precipitation and future extreme precipitation. The figure below presents the results of related analysis carried out by the MARISA team that examined how changes in future precipitation events lead to urban flooding in Pittsburgh, Pennsylvania.

This figure is based on an analysis of three projections of future precipitation, shown by the three models in the figure, compared to estimated historical precipitation events from NOAA’s Atlas 14.1 Using each dataset, the study team compared recent estimates of climate adjusted precipitation depths for combinations of event duration (e.g. 1-hour to 24-hour) and frequency (e.g. 100-year return period).2 These are shown in the top panel. These estimated projected and historic precipitation depths were then used as inputs to a stormwater model that calculated runoff and inundation depths across an urban catchment in Pittsburgh – Negley Run. The maps show a selection of streets and intersections in the catchment area prone to flooding that could be represented in the simulation model. While specific to Pittsburgh, this study shows how increases in extreme precipitation events translate into urban flooding and offers a case study of solutions that may be relevant to other locations.

Key Findings

  • Temperatures were above normal across the Mid-Atlantic, with much of the region experiencing temperatures up to 0–2 degrees Fahrenheit above normal and some locations in Virginia, Maryland, Pennsylvania, and New York experiencing some of their warmest spring months on record.
  • It was generally dry across the region, with much of Virginia experiencing 50–75% of normal rainfall. Only a small portion of the watershed, primarily in southern New York, experienced above normal (100–125%) precipitation.
  • Warm and dry weather across the region was further underscored by low March snowfall, particularly in Scranton, Williamsport, and Harrisburg, Pennsylvania; Binghamton, New York; Baltimore, Maryland; and Washington, D.C.
  • The 2021 Atlantic Hurricane Outlook forecasts an above-average probability for major hurricanes for the 2021 Atlantic hurricane season, with NOAA predicting 13–20 named storms, six to ten hurricanes, and three to five major hurricanes.
  • A case study of urban flooding in Pittsburgh shows substantially greater rainfall depths and resulting flooding associated with precipitation events estimated with future climate model data than under Atlas 14 estimates.

How to Use the Tool

Selecting Time Periods and Locations
Use the Select Duration and Select Return Period slider bars to adjust the design storm shown in the graph and resulting flood estimate in the map.

Technical Notes

NOTE: The return periods shown in the figure above represent the likelihood of a precipitation event occurring in a given year. A 100-year return period, for example, has a one percent chance of occurring in a given year, and a 50-year return period has a two percent change of occurring in a given year.

The orange points shown represent additional locations flooded under future climate model-based estimates. The blue points represent locations flooded under both Atlas 14 and climate model-based estimates.

Downscaled climate model data was obtained for the North America Coordinated Regional Downscaling Experiment (NA-CORDEX) for Pittsburgh, Pennsylvania. The three models shown in the tool include: Climate Model 1 - MPI-ESM-LR RegCM4; Climate Model 2 - GFDL-ESM2M WRF; Climate Model 3 - MPI-ESM-LR WRF. More details on these models can be found at: https://na-cordex.org/simulation-matrix.html. More details on the modeling and full study can be found at: Fischbach, Jordan R., Michael T. Wilson, Craig A. Bond, Ajay K. Kochhar, David Catt, and Devin Tierney, Managing Heavy Rainfall with Green Infrastructure: An Evaluation in Pittsburgh's Negley Run Watershed. Santa Monica, CA: RAND Corporation, 2020. https://www.rand.org/pubs/research_reports/RRA564-1.html.

Footnotes

  1. https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html?bkmrk=pa Return to text ⤴

  2. https://https://link.springer.com/article/10.1007/s10584-019-02649-6 Return to text ⤴

Related Tool

  • Changes in Future Extreme Precipitation

    This tool is an interactive map of the Chesapeake Bay watershed that provides gridded estimates of how projections of future extreme precipitation—the number of days each year with precipitation above a 1", 2" or 3" threshold—during 30-year periods (2006-2035, 2036-2065, 2066-2095) and under two future emissions scenarios, compare to a historic 30-year average (1976-2005).

View all the climate data tools