Indicator: Annual Precipitation Change (1901-2021)

<p><strong>Access the Indicator Materials:</strong><br />- <a target="_blank" href="https://d18lev1ok5leia.cloudfront.net/chesapeakeprogress/chart-assets/change-in-total-annual-precipitation-in-the-chesapeake-bay-watershed-1901-2017/Analysis-and-Methods_2021_Total-Precipitation_072523_final.pdf">Analysis &amp; Methods</a><br />- <a target="_blank" href="https://d18lev1ok5leia.cloudfront.net/chesapeakeprogress/chart-assets/change-in-total-annual-precipitation-in-the-chesapeake-bay-watershed-1901-2017/Data_2021_Climate-Indicators_4.27.2023-2.xlsx">Data File</a><br />- <a target="_blank" href="https://gis.chesapeakebay.net/ags/rest/services/ChesapeakeProgress/cpClimate_Precipitation/MapServer">Map Service</a></p><p>This metric is based on precipitation data collected from land-based weather stations and compiled in NOAA’s nClimDiv dataset, which is maintained by the National Centers for Environmental Information. The nClimDiv analysis averages climate data across U.S. climate divisions, and precipitation trends are calculated from annual anomalies using ordinary least-squares regression. The trend is then converted to total change over the full period of record and expressed as a percent change relative to average precipitation during the 1901–2000 baseline period.</p><p><strong>Note: This Indicator supported progress tracking toward the Monitoring and Assessment Outcome in the original Chesapeake Bay Watershed Agreement, adopted in 2014. The Watershed Agreement and Adapting to Changing Environmental Conditions Outcome were revised in 2025.</strong></p>