Changes in Seasonal Total Precipitation from 1976 to Present

This tool is excerpted from Chesapeake Bay Watershed Climate Impacts Summary and Outlook for Winter 2018-2019.

Key Findings

  • In general, the region has experienced increases in summer seasonal precipitation from 2006-2017 compared to historical averages, with higher percentage increases in the eastern half of the Chesapeake Bay Watershed.
  • Southeastern Chesapeake Bay has seen notable decreases in winter and spring total precipitation.

How to Use the Tool

Viewing individual locations trends over time:
By holding your mouse over an individual grid cell, a window that shows trends in the seasonal total precipitation will pop up. This data was calculated for each year of the analysis and for each grid cell.

Filtering by geography:
Using the dropdown menu, users should first select a geographic level—the entire watershed, state, county or municipality. A list of states, counties or municipalities will appear, and individual locations can then be selected.

Technical Notes

The ChesWx gridded climate datasets contain daily interpolations of precipitation and temperature observations for the Chesapeake Bay watershed, as well as the broader Mid-Atlantic and surrounding regions. Data are available from 1948 to 2017 at 4km spacial resolution. For this study, we utilized ChesWx daily precipitation data over the Chesapeake Bay watershed from 1976 to 2017. Access ChesWx data and learn more about the ChesWx methodology and input datasets.

Seasonal total precipitation was determined for each season by summing all daily precipitation events that occurred for each three-month season. We calculated seasonal total precipitation for each season for each year and the averaged values for each season across 30-year periods – 1976-2005, 2006-2035, 2036-2065, 2066-2095 for LOCA data for both RCP 4.5 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. Winter is defined as December, January and February. Spring is defined as March, April and May. Summer is defined as June, July and August. Fall is defined as September, October and November.

  • Changes in Future Seasonal Total Precipitation – Chesapeake Bay Map

    Mar 25, 2019

    This tool is an interactive map of the Chesapeake Bay watershed that provides gridded estimates of how projections of winter, spring, summer and fall total precipitation during 30-year periods (2006-2035, 2036-2065, 2066-2095), under two future emissions scenarios, compare to a historic 30-year average (1976-2005) of total precipitation for each season.

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