Long-term precipitation and drought trends in the US
Data compiled by NOAA and the Environmental Protection Agency indicates that extreme rainfall events are becoming increasingly common across portions of the United States, while droughts are becoming more common and severe across the Southwestern states.
Since the start of the 20th century, annual rainfall has increased from the eastern Plains to the Northeast U.S. but has decreased across large portions of the West.
In addition, the percentage of land area in the U.S. that has experienced unusually high annual precipitation has increased over the past 20 years.
More and more land areas are also being impacted by extreme, one-day precipitation events, especially over the past 50 years.
The number of extreme precipitation events in the U.S. has also been trending steadily upward over the past several decades. In addition to climate change, some of the reasoning for this may also be due to increased observation of these events by better surface observation coverage and doppler radar.
With these changes in precipitation, we are also seeing an uptick in the frequency of river flooding, especially over the Midwest, Northeast and Pacific Northwest since the middle 1960s.
There has been a decrease in drought across much of the eastern half of the country since the start of the 20th century. However, drought is becoming more common in other areas, especially across the Southwest.
