As land condition deteriorates, flooding and droughts become common.

As the Mississippi River's catchment area got converted from prairie and forest to agricultural land, major floods* increased from three in 100 years (1844-1943), to four in 35 years (1944-1978), to four in 15 years (1979-1993). The river flooded these grain silos at MacGregor, Iowa (central U.S.A.) in April 2003.

* Measuring 9 meters (30 feet) or more at St. Louis, Missouri