Floods and Drought

1. Droughts are long periods (over one year) of below-average precipitation. The most recent drought to affect the Northern Plains was during the years 1988-1989. The most notorious drought was the Dust Bo wl, affecting much of the middle of North America during the mid 1930's. One way to quantify the magnitude of drought is the Palmer Drought Severity Index (PDSI). A PDSI near zero indicates moisture conditions are near climatological averages, while negative values mean drier than average conditions exist over a region, and positive values signify wetter than average conditions.

1. national
2. regional

2. Floods can occur anywhere. On average in the U.S. each year, nearly 75,000 people are evacuated from their homes and more than $250 million in property damage occurs (Federal Emergency Management Agency statistics). I n the Grand Forks 1997 flood, over 60,000 people were evacuated and property damage could exceed $2 billion.

1. Recent floods in the region and around the world

   1. Grand Forks 1997 flood
   2. Great flood of 1993 on the Mississippi and Missouri Rivers
   3. Oregon 1996 flood
   4. Asian floods in 1996

3. Flash floods have occurred in many areas of the U.S. They can arise with little or no warning and have the potential for massive destruction.

1. Rapid City, South Dakota, flash flood of 1972
2. Buffalo Creek, Colorado, flash flood of 1996