BAMOS Vol 30 No. 4 2017 | Page 34

BAMOS Dec 2017
Figure 4 . Number of tornadoes reported in 30-year periods in Tasmania , Australia , between 1927 and 2016 ( Bureau of Meteorology , 2016b ).
wind speed trends remained relatively unaltered ( Figure 1 ) ( Bureau of Meteorology 2016a ). Contrary to this , although the Orford ( Aubin Court ) site also displayed a steady trend in long-term wind speeds ( Figure 1 ), it did not appear to have the similar wind speed monitoring equipment upgrades as did the previous sites ( Bureau of Meteorology 2016a ). Although this in itself is not a guarantee that equipment upgrades over time have not had an effect on wind speed measurement records , for the purpose of studying the generalised long-term negative ( decreasing ) and positive ( increasing ) trends in wind speeds across Tasmania , any measured effects of change induced by equipment upgrades is hereby considered as being marginal .
intensifying westerlies . McKendry et al . ( 1986 ) had also found that the Southern Alps , and surrounding land and sea features of Canterbury , New Zealand , affected localised airflow patterns , and thus localised wind regimes . Using the International Pacific Research Center regional climate model , a study by Sen et al . ( 2004 ) found that deforestation of the Indochina Peninsula has far-reaching effects on the East Asian summer monsoon , significantly altering rainfall distribution patterns while also increasing local westerly wind speeds . Climate change , the Tasmanian geomorphology , and deforestation practices in Tasmania are all therefore potential contributive factors of the wind speed features currently observed in Tasmania .
3.2 The zone of increasing wind speeds
Flanked on the east and west sides by decreasing wind speeds , the zone of increasing wind speeds was observed to extend from central northern Tasmania , through to southeastern Tasmania , appearing to form a central ‘ corridor ’ of increasing wind speeds ( Figure 3 ). Increasing wind speeds range from an average of 1.12 % to 20.78 % every decade ( Figure 3 ). Outside of the zone , the average decreasing wind speeds vary from 0.26 % to 11.99 % every decade ( Figure 3 ). As 30 % of the sites used in Figure 3 only have two data points ( Figure 2 ), the zone may not be validated by future recorded wind speed measurements . If wind speed measurements across the current Tasmanian sites are maintained , future thirty-year mean annual wind speed data sets available at the end of 2020 and beyond , may either enhance or negate the currently observed zone .
Due to a changing climate , Böning et al . ( 2008 ) found a significant intensification of the Southern Hemisphere prevailing winds ( westerlies ) between the latitudes of 30 ° and 60 ° S , over the past few decades . Tasmania is geographically located within those
3.3 Tornadoes
Since records have begun , the frequency of tornadoes observed in Tasmania have steadily increased by 2 – 3 per decade ( R 2 = 0.98 ) ( Figure 4 ).
Over 86 % of recorded tornadoes occurred within the zone . However , due to Tasmania ’ s relatively small population and large areas of remoteness , tornado events located outside of the zone may not have been adequately accounted for , therefore contributing towards a level of uncertainty in the actual number and distribution of tornadoes that occur across Tasmania , and its potential correlation with the zone . The population density of people living in various locations around Tasmania has also changed over time ( ABS 2017 ). As the population density in areas change , the probability that tornadoes are observed and reported depending on a particular location may over time also be significantly affected . As this study did not include an analysis of the potential population density effects on tornado sightings over time , it must therefore be acknowledged that