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Precipitation
Trends
  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.
U.S. Environmental Protection
Agency
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