DOT Center for Climate Change | About Transportation and Climate Change

Precipitation has increased by about 1 percent over the world's continents in the last century. High latitude areas are tending to see more significant increases in rainfall, while precipitation has actually declined in many tropical areas.

In North America, precipitation has increased significantly. Precipitation in the United States has increased by an average of about 5 percent in the last century. Along the northern tier states and in Southern Canada, rainfall has increased 10-15 percent. Much of the increase in rainfall has been taking place between September and November. Rainfall is also tending to be more concentrated in heavy downpours, according to studies by the National Oceanic and Atmospheric Administration NOAA. At the beginning of the 20th century, only 9 percent of the nation experienced a storm each year in which more than two inches of precipitation fell in a 24-hour period. In recent decades, such a severe storm has occurred each year over close to 11 percent of the nation.

Precipitation Trends, 1900 to Present

Precipitation Trends, 1900-present
Red circles reflect increasing precipitation;
Blue circles reflect decreasing precipitation

Precipitation of the USA Affected by Much Above
Normal Portion of Annual Precipitation From
Extreme Events

bar graph showing Precipitation from extreme events from 1900-present
The change in the area of the USA affected by increases
in the proportion of total annual precipitation derived
from extreme daily precipitation events (more than 2 inches)