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(b) Flooding can be as frequent as the occurrence of a spring rain or summer thunderstorm. The amount of precipitation produced by storm events determines the type of flooding. Flash floods, which typically occur more frequently than general floods, occur along small streams and creeks of the type that are present throughout Cabarrus County. The undermining or washing out of roads is typically associated with flash floods. General flooding occurs less frequently and as the result of much larger storm events such as hurricanes. These larger storm events occur along the East Coast of the United States most often in the late summer and fall. (c) The total economic and loss of life impact depends greatly on the amount of development within the area. Currently, Cabarrus County has a moderate amount of development, mostly residential, along the floodplains of major streams and Rocky River. Both flash flooding and longer -term general flooding can cause massive damage and destruction to the structures located in these floodplains. 3. Tornadoes (Map A -1 Cabarrus County Multi- Hazards) (a) Tornadoes, typically the by- product of a larger storm, are violently rotating columns of air that come in contact with the ground. Tornadoes are produced during severe thunderstorms, which are created near the junction between warm, moist air and cold, dry air. Tornadoes derive their energy from the heat contained in warm, moist air masses. Tornadoes do not form during every thunderstorm. They occur when the moist, warm air is trapped beneath a stable layer of cold dry air by an intervening layer of warm dry air. This is called an inversion. If this is disturbed, the moist air will push through the stable air that is holding it down. This warm air will then condense as the latent heat it holds is released. This air will then spiral upwards. With the help of different types of winds, this spiral gains speed, producing a tornado. (b) Intensity. Tornadoes have a more localized impact than a hurricane. Tornadoes generally produce a narrow path of concentrated destruction from 0.01 mile wide to greater than 1 mile wide, but are generally less than .6 miles wide. Tornadoes may also produce paths of destruction from less than 1 mile in length to greater than 100 miles in length. The destruction caused by tornadoes may range from light to severe depending on the path of travel. Typically, structures of light construction, such as residential homes, suffer the greatest damage from tornadoes. A tornado will rarely last longer then 30 minutes. The combination of conditions that cause tornadoes are common across the southern U.S. in early spring, especially in April and May. Tornado intensity was originally measured using the Fujita- Pearson Scale. In February 2007, the Enhanced Fujita (EF) scale replaced the original Fujita scale in all tornado damage surveys in the United States. Annex A Hazard Identification and Analysis A -3 1 Deceathenr2MRimber s F -6 Page 107