Projected Changes in Total Monthly Precipitation

Projected Changes in Total Monthly Precipitation

This tool is excerpted from Chesapeake Bay Watershed Climate Impacts Summary and Outlook for Spring 2022.

Tool Background

Planning for future changes in precipitation necessitates an understanding of not only how precipitation is changing from year to year but also how climate change is shifting precipitation within a year. The distribution of precipitation within a year has important implications for water supply planning, stormwater management and flood control, irrigation for agriculture, among many other applications. For example, a shift from high precipitation during the spring to more during winter could impact crop yields or place greater demands on water for irrigation. Over recent decades, research has shown that the Northeast has experienced an increase in precipitation, particularly during the winter months, and that this trend is expected to continue into the future.1

This assessment focuses on the understanding these trends for the Mid-Atlantic region specifically. Figure 5 shows how total monthly precipitation is projected to change in the future compared to an historical baseline (1950–2020), as well as the climate normal (1991–2020).

Key Findings

  • In an analysis of total monthly precipitation, the Mid-Atlantic is projected to see an increase in precipitation compared to two historical time periods: 1991–2020 and 1950–2000.
  • At both regional and state scales, total monthly precipitation during the winter months is projected to experience the greatest increase into the future, while the fall months are projected to experience smaller increases or even decreases in precipitation.

Figure 1. Projected Changes in Future Total Monthly Precipitation

How to Use the Tool

Selecting Time Periods and Future-Emissions Scenarios
Use the list to the right of the maps to adjust the period used to calculate changes in future precipitation relative to two different baselines (a historical baseline: 1950–2000 and the climate normal: 1991–2020). Users can also select the future emissions scenario (Low or High Emissions).

Viewing Data for a State or County
You can use the State and County filters to the right of the table to have the plot show data for a particular location of interest.

Technical Notes

Localized Constructed Analogs (LOCA) is a downscaled climate data product available at 1/16-degree (6-km) resolution over the continental United States. LOCA data sets2 include the 32 climate models available in the Coupled Model Intercomparison Project 5 (CMIP5) archive, for two future greenhouse gas concentration trajectories: a low emissions future, Representative Concentration Pathway (RCP) 4.5;3 and a high-emissions future, RCP 8.5.4 For this study, we used LOCA data over the Chesapeake Bay watershed from 1950–2100 (or 2099 for some models) for calculations of the baseline periods and the percent differences from those baselines. Access LOCA datasets and learn more about the methodology.

Data were processed by the Northeast Regional Climate Center to calculate total monthly precipitation.


  1. Dupigny-Giroux, L.A., E.L. Mecray, M.D. Lemcke-Stampone, G.A. Hodgkins, E.E. Lentz, K.E. Mills, E.D. Lane, R. Miller, D.Y. Hollinger, W.D. Solecki, G.A. Wellenius, P.E. Sheffield, A.B. MacDonald, and C. Caldwell, 2018: Northeast. In Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 669–742. doi: 10.7930/NCA4.2018.CH18 Return to text ⤴

  2. Return to text ⤴

  3. More information on RCP 4.5 can be found in: Return to text ⤴

  4. More information on RCP 8.5 can be found in: Return to text ⤴

  • Changes in Future Seasonal Total Precipitation – Chesapeake Bay Map

    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.

View all the climate data tools