An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »


Description of Changes in Climatic Indices in USA over 25 Years (1989 – 2013)

This report concentrates on the methodology and potential future uses for long-term climate factor trends, and trends of derived climatic factors and indices. Analyses of all factors over the 25 years (1989- 2013) show the magnitude and direction of significant changes on different time scales (monthly, annual average, and seasonal). 

You may need a PDF reader to view some of the files on this page. See EPA’s About PDF page to learn more.