Climate Change and Rainfall

This information supplements the "Climate Change and Rainfall" section of the Rain Garden Manual for Vermont and the Lake Champlain basin. It will help you prepare for the rain storms of the future and size your rain garden accordingly.


Rainfall extremes intensify as the climate warms. Oceans encompass almost 70% of the Earth’s surface, and as global temperatures increase, more water will evaporate into the atmosphere from oceans, lakes, and soils. Every increase of 1°F temperature enables the atmosphere to hold 4% more water vapor. This increase in water vapor held by the air is predicted to result in more frequent and heavier downpours, which can amplify the risk and severity of flooding. Data compiled by the National Atmospheric and Atmospheric Administration (NOAA) show: 

  • Temperatures in Vermont have increased more than 2°F since the beginning of the 20th century. 
  • Average annual precipitation is projected to increase in Vermont over the 21st century, particularly during winter and spring. Corresponding increases in temperature will increase the proportion of precipitation falling as rain rather than snow. 
  • Extreme precipitation events are projected to increase, potentially increasing the frequency and intensity of floods. 

Source: NOAA State Climate Summaries (data through July 2020) 

Supplemental Information