Changes in Future Extreme Precipitation

This tool is excerpted from Chesapeake Bay Watershed Climate Impacts Summary and Outlook for 2018.

Key Findings

  • Nearly all future periods and future emissions scenarios show some increase in the number of days each year with precipitation above 1”, 2” and 3” thresholds.
  • By mid to late 21st century, the majority of the Chesapeake Bay Watershed could experience a doubling of annual extreme precipitation events over 2” and 3” compared to historical averages, under the higher emissions scenario.
  • This suggests the challenges the region already experiences with respect to urban and coastal flooding could be magnified and more frequent in the future.

How to Use the Tool

Select a Daily Precipitation Threshold to show number of days with precipitation above a 1", 2" or 3" threshold.

Use the Time Period slider to adjust the future time period used to calculate the projected change in precipitation. For each time period, select a future greenhouse gas emissions scenario of moderate future emissions that peak in 2040 and then decline (known as RCP 4.5) or high future emissions that rise to 2100 (known as RCP 8.5).

Click or tap a grid cell to shows trends in the number of annual extreme precipitation events. This data was calculated for each year of the analysis and will change as you select different metrics, years and future emissions scenarios.

Technical Notes

LOCA or Localized Constructed Analogs is a downscaled climate data product available at 1/16thdegree (6 km) resolution over the continental United States. LOCA datasets include the 32 climate models available in the CMIP5 archive, for two future greenhouse gas concentration trajectories – RCP 4.5 and RCP8.5. For this study, we utilized LOCA data over the Chesapeake Bay watershed from 1976-2095. Access LOCA datasets and learn more about the methodology.

We calculated the number of days above 1 inch, 2 inch and 3 inch daily precipitation thresholds for each year across the Chesapeake Bay watershed using both the ChesWx and LOCA daily precipitation data products. The annual counts above these thresholds were then averaged across 30-year periods – 1976-2005, 2006-2035, 2036-2065, 2066-2095 for LOCA data for both RCP4.5 and RCP 8.5 and 1976-2005, 2006-2017 for ChesWx data. To average across climate models for each grid cell in the LOCA dataset, we employed a weighted average provided by the Northeast Regional Climate Center. Both LOCA and ChesWx datasets were masked to the boundaries of the Chesapeake Bay watershed before calculating seasonal precipitation values and the spatial resolution of each dataset was preserved.

  • Changes in Extreme Precipitation from 1976 to Present

    Nov 27, 2018

    This tool is an interactive map of the Chesapeake Bay watershed that provides gridded estimates of how extreme precipitation - the number of days each year with precipitation above a 1", 2" or 3" threshold - from 2006-2017 has changed compared to a historic 30-year average (1976-2005).

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