The Impact of Severe Thunderstorms
Severe thunderstorms are very localised events, not usually affecting wide areas as tropical cyclones and floods do, so their devastating impact is often underestimated. These thunderstorms can occur anywhere in Australia and do so more frequently than any other major natural hazard. Each year severe thunderstorms are responsible, on average, for more damage (as measured by insurance costs) than tropical cyclones, earthquakes, bushfires and floods. Unfortunately, severe thunderstorms also kill people; between five and ten deaths are caused by lightning each year. Deaths also occur when strong winds cause tree limbs to fall, debris or other loose items to become projectiles and small craft in open waters to capsize. In fact, although many people believe that tornadoes do not occur in Australia, tornado-related deaths have occurred here.
Severe Thunderstorm Definition
Thunderstorms which produce any of the following events are classified as severe in Australia:
- large hail (2 cm in diameter or greater)
- wind gusts (90 km/h or greater)
- heavy rainfall conducive to flash flooding
Severe thunderstorms are likely to cause damage to property, crops and natural vegetation and, as we have seen, may even result in death or injury.
Who are the Storm Spotters?
In 1989, the Bureau of Meteorology (the Bureau) undertook to establish a national network of severe thunderstorm spotters whose primary task is to report on severe weather caused by thunderstorms in their area. This followed the success of similar networks implemented by overseas weather agencies in countries such as Canada and the United States of America.
The Australian network now accounts for a large proportion of severe weather reports received by the Bureau and their timely information helps Bureau forecasters to prepare and update severe weather warnings. Storm spotters also have an impact on Australian research into severe thunderstorms by providing a better picture of the frequency and distribution of these violent events. In some areas, spotters are also encouraged to report on other dangerous weather phenomena, for example widespread damaging winds.
Storm spotters are volunteers recruited from the ranks of weather enthusiasts and public-minded people all across Australia. Thousands of people from all walks of life are now involved, including members of the police, emergency services and fire agencies, as well as climate, rainfall and river observers and students. Together they provide a vital service for the benefit of their neighbours and the community in general.