When these rain drops reach high levels they freeze, forming hail stones. These hail stones then grow steadily in size as they are carried up and down by strong currents of air. Hail stones larger than tennis balls have been recorded in Australia. Hail can also occur when a cyclone forms.
Cyclones are formed near the equator. The sun heats the sea, and some water evaporates. Clouds build up, and a low pressure system starts these clouds rotating. As the clouds build up speed they form a cyclone. Cyclones occur most frequently off the northwest coast of Western Australia, in the Gulf of Carpentaria and in the Coral Sea. Cyclones are often confused for tornadoes, which are formed in a different way.
Tornadoes form during thunderstorms when hot air meets cold air large amounts of wind can be produced by the warming and cooling of the air. A tornado can range in width from a few metres to several hundred metres in width. Tornadoes spin clockwise and contain winds that may reach more than 300 km/h. Thunderstorms can also cause flash flooding.
Flash flooding occurs during thunderstorms. Moist air condenses when it reaches high attitudes. When rain drops become too large to be supported they are supposed to fall, but the intense winds and updraught of a severe storm can stop the rain from falling. As the updrafts loose strength the rain released all at once. The effects on low lying land can be devastating as the water runs downhill and collects in low lying areas.
Australia is a hot and dry country and is incredibly fire-prone. High temperatures, strong winds, low humidity and large amounts of combustible vegetation provide perfect conditions for bushfires to thrive. Bushfires can occur anywhere in Australia.
All of the disasters mentioned above have the potential to inflict ruthless and unexpected stresses on society. These include death, injury, property damage, loss of production and income for many people, such as farmers. Disasters such as bushfires, earthquakes and droughts can cause some or all of these conditions.
Bushfires pose the most threat to life and property. Earthquakes damages property and can cause loss of life and injury. Droughts in both agricultural and pastoral areas have widespread effects including significant reduction of harvests, livestock losses and shortage of water in urban areas. All of these create extreme financial losses for farmers and rural workers can be economically devastating. Excessive amounts of rain, though rare, can also be damaging to agricultural areas.
As mentioned above long, sustained periods of intense rainfall are rare, although very intense thunderstorms, often with hail, lasting only a few minutes can cause damage to crops and freshly cultivated soil. Thunderstorms can damage urban areas too, large hail stones can hit cars, buildings and even people. Flash flooding associated with these intense thunderstorms rarely lasts long, but the sudden rise in water levels damages property, and can cause injury and death.
