100-year flood

A one-hundred year flood is calculated to be the maximum level of flood water to be expected in an average one-hundred-year period. Sometimes, a 500-year flood is also calculated. Based on the expected water level, an expected area of inundation may be mapped out according to elevation above sea level. This area figures very importantly in building permits, environmental regulations, and flood insurance.

In 2002 100-year floods caused by over a week of continuous heavy rains ravaged Europe, killing dozens, dispossessing thousands, and causing damages of billions of dollars in Russia, the Czech Republic, Austria, Germany, Romania, Spain, Croatia, Italy, and Bulgaria.

Also see topographic map, extreme weather, extreme value theory