BAMOS Vol 30 No. 4 2017 | Page 30

30 BAMOS Dec 2017 Science Article Observed zone of increasing wind speeds and tornado events in Tasmania, Australia Anton Kole Recently completed Honours student (first class), The University of Tasmania email: [email protected] Abstract While wind speeds around some parts of Tasmania have been observed to be increasing over time, some areas have been decreasing. The increasing wind speeds currently form a zone from the central northern part of Tasmania, through to southeastern Tasmania. Within the increasing wind speed zone (the zone), wind speeds vary from an increasing average of 1.12% to 20.78% every decade. Outside of the zone, the average decreasing wind speeds vary from 0.26% to 11.99% every decade. The frequency of tornado sightings in Tasmania has been steadily increasing since 1928, with approximately 86% occurring within the zone. If the wind speed in the zone continues to increase, tornado events may also correspondingly increase. Despite some remaining concerns about the quality of long-term wind observations, the observed changing patterns may potentially signify the initial conditions of an emerging Tasmanian ‘Tornado Alley’. Although elements leading to these conditions are not yet fully understood, climate change, the Tasmanian geomorphology, and deforestation practices may be contributing factors. 1. Introduction With extreme weather event intensity and frequency expected to increase over time due to climate change (White et al., 2010), a previous study found that in some areas of Tasmania wind speeds have been steadily increasing (Kole, 2016). Extreme wind events may cause severe damage to crops, private property, and public infrastructure. Tasmanian businesses, crops, lives, and economy, have been adversely affected by such events (ABC, 2014; ABC, 2015). Understanding which areas of Tasmania are most affected by increasing wind speeds may assist stakeholders to be better able to prepare for, and adapt to changing climatic conditions. While a previous report has provided a range of wind speed projections based on derived information, modelled hazards, and computational methodology (Cechet et al., 2012), this study aims to assess and provide stakeholders with information as to which areas of Tasmania are potentially likely to experience increasing wind speeds over the coming decades based on observed trends in measured wind speed records. 2. Data and methodology 2.1 Study area The area of study included all of Tasmania, Australia, and its smaller satellite islands. Being the largest island State of Australia, Tasmania has a land mass of 68,423 km², is located 42°S 147°E, and has a population of approximately 509,965 people (ABS, 2007; ABS, 2016). Centrally located and extending from northwest to southeast, Tasmania’s central highlands consist of numerous plateaus, lakes, and mountain ranges. 2.2 Data collection All wind speed data were obtained from the Australian Bureau of Meteorology (Bureau of Meteorology) website (Bureau of Meteorology, 2016a; Bureau of Meteorology, 2016b). The statistical weather data collected consisted of 9 am and 3 pm thirty-year mean annual wind speeds from 22 different weather station sites (sites) from across Tasmania (Table 1). Data in Figure 1 were also included from sites that were no longer currently collecting wind speed data, stopping as far back as 1959. The coordinates of all sites were also obtained for mapping purposes. 2.3 Methodology Wind speed data collection and thirty-year mean annual 9 am and 3 pm wind speed calculations were performed by the Bureau of Meteorology, and subsequently made available online (Bureau of Meteorology 2016a; Bureau of Meteorology 2017). Climate statistics were derived only when there was at least 10 years of data available (Bureau of Meteorology 2007). An average of the 9 am and 3 pm thirty-year mean annual wind speeds from each of the weather stations were calculated, and used throughout this study as data-points (Figure 1 and Figure 2).