Cyclones (synonyms: hurricanes, typhoons)

 

Damage to the Sundurban mangrove forests in Bangladesh after Tropical Cyclone Sidr in 2007 © Flickr/joiseyshowaa

Cyclones (a system of winds rotating inwards to an area of low barometric pressure) can and do occur at any latitude and in any climate. Those occurring within 30 degrees north or south of the equator are called tropical cyclones; those found above 60 degrees north or south of the equator are arctic or polar cyclones; and those between 30 and 60 degrees are called extratropical cyclones.

The terms 'hurricane' and 'typhoon' are regionally specific names for a strong tropical cyclone:

  • western North Pacific Ocean and South China Sea - typhoon
  • Atlantic Ocean, Caribbean Sea, and in the eastern North and central Pacific Ocean – hurricane
  • Indian Ocean and South Pacific region – tropical cyclone

Three primary features of cyclones that cause damage are rainfall, storm surges and winds.

Torrential rains accompanying tropical cyclones frequently cause extensive flooding, leading to tree mortality from anoxia (absence of oxygen). Flooding and rainfall saturates soil, which may increase susceptibility to windthrow in shallow soils.

Wind is the feature that is linked to a vast majority of a cyclone’s damage, both directly and indirectly, through waves and storm surge. The most common impacts of wind include defoliation, loosening and shredding of bark, and abrasion of stem surfaces. Trees can sway, twist and rock, and large branches may break off and cause damage to understory trees. Individual stems may bend, break or suffer some level of uprooting from leaning to complete blowdown of the tree.

A storm surge is a large dome of water, sometimes greater than five metres, that floods the coast at high speed and with immense force as the storm makes landfall. Storm surges can cause extensive damage to coastal vegetation by bending, breaking or uprooting trees. Scouring and erosion may expose root systems leading to desiccation, and deposition may lead to root suffocation. Salinity and inundation increased by the storm surge can cause plant and tree mortality.

last updated:  Friday, June 28, 2013