Tropical cyclones and the ecohydrology of Australia's recent continental-scale drought (original) (raw)
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Contribution of tropical cyclones to extreme rainfall in Australia
International Journal of Climatology, 2015
The contribution by tropical cyclones (TCs) to extreme rainfall in Australia is examined using daily rainfall measurements from over 2000 rain gauges. Analyses focus on the period beginning with regular satellite monitoring of TCs (1969/1970) through the year 2012/2013 and consider daily and multi-daily annual maximum rainfall series. Our results indicate that TCs play a prominent role in extreme rainfall over much Australia, with more than half of the highest annual rainfall events associated with these storms over the coastal regions and in particular over Western Australia. Moreover, the TC fractional contribution to extreme rainfall increases as we focus on the largest rainfall events, with approximately 66-100% of annual maxima in excess of 100 mm (∼4 inches) over Western Australia associated with TCs at over one third of the locations. Given the well-established controls on Australian TC activity by the El Niño-Southern Oscillation (ENSO), we also examined the relationship between extreme rainfall associated with TCs and ENSO using logistic regression. A larger probability of having an annual rainfall maximum related to TCs occurs during La Niña years, consistent with enhanced Australian cyclogenesis during these phases of ENSO. We also highlighted regional differences in the link between ENSO and extreme rainfall events, highlighting the stronger connection along the coastal areas and in particular over Western Australia.
Tropical cyclones in the Australian/southwest Pacific region
1983
Some results are presented from the completed first stage of a collaborative Colorado State University/Australian Bureau of Meteorology project to investigate various aspects of tropical cyclones in the Australian/southwest Pacific region. We begin with a brief description of ...
Tropical cyclone trends in the Australian region
Geochemistry, Geophysics, Geosystems, 2008
Tropical cyclone trends in the Australian region are examined using the Bureau of Meteorology best track data. Here the focus is on analyzing differences in trends between the eastern and western subregions of the Australian formation region, under the assumption that any spurious trends in the best track data due to changes in observational practices would be less noticeable in differences between two adjacent portions. Substantial differences in trends are found between the two subregions, with the number, average maximum intensity, and duration at the severe category intensities of tropical cyclones increasing since 1980 in the west but decreasing (in number) or exhibiting no trend (in intensity, severe category duration) in the east. Analyses of trends in atmospheric variables known to be related to tropical cyclone characteristics also indicate substantial differences between the two subregions.
On the recent hiatus of tropical cyclones landfalling in NSW, Australia
Journal of Southern Hemisphere Earth Systems Science, 2020
It is well known that severe storms result in some of the costliest natural disasters for New South Wales (NSW), Australia. However, it is not widely acknowledged that some of these events are, in fact, a result of landfalling tropical cyclones (TCs). Indeed, the intense focus of TC research within the tropics generally disregards landfalling TC events in the mid-latitude regions of Australia. This is likely due to the perceived infrequency of these events compared to other more susceptible regions. Therefore, in this study, we review this assumption by developing a 150-year record of TC activity, based on a range of digitised and analogue historical datasets and identify 30 individual landfalling TCs that have impacted NSW. Periods of enhanced and reduced TC activity are observed, with a defined hiatus (absence of landfalling TCs) after approximately 1980. The recent decrease in TC activity is subsequently linked to an increase in El Niño activity and warming of north-west Australi...
Remote forcing of water levels by tropical cyclones in southwest Australia
Continental Shelf Research, 2010
Tropical cyclones (termed hurricanes and typhoons in other regions), are extreme events associated with strong winds, torrential rain and storm surges (in coastal areas) and cause extensive damage as a result of strong winds and flooding (caused by either heavy rainfall or ocean storm surges) in the immediate area of impact. The eastern Indian Ocean, particularly in the northwest region of Australia, is impacted by up to 10 tropical cyclones during the cyclone season, although direct impact of cyclones along the west and southwest coastlines is rare. However, the sub-tidal frequency component of sea level records along the west and south coasts of Western Australia indicates lagged correspondence with the occurrence of tropical cyclones. It is demonstrated that the tropical cyclones generate a continental shelf wave which travels along the west and south coasts of Australia up to 3500 km with speeds of 450–500 km day−1 (5.2–5.8 ms−1) with maximum trough to crest wave height of 0.63 m, comparable with the mean daily tidal range in the region. The shelf wave is identified in the coastal sea level records, initially as a decrease in water level, 1–2 days after the passage of the cyclone and has a period of influence up to 10 days. Amplitude of the shelf wave was strongly affected by the path of the tropical cyclone, with cyclones travelling parallel to the west coast typically producing the most significant signal due to resonance and superposition with local forcing. Analysis of water levels from Port Hedland, Geraldton, Fremantle and Albany together with cyclone paths over a ten year period (1988–1998) indicated that the tropical cyclones paths may be classified into 6 different types based on the amplitude of the wave.
Australian …, 2008
The potential risks to life and property from tropical cyclones (TCs) in northern Australia are significant and the accuracy of historical TC data-sets is of special interest to those involved in the quantitative assessment of these risks, especially in the marine environment. To this end, the offshore oil and gas industry in northwestern Australia has collectively been at the forefront of TC risk monitoring, modelling and risk assessment since the early 1970s. This work has underpinned the extensive investments onshore (pipelines, ports, processing and housing), offshore (pipelines, platforms, floating production systems),
Natural hazards in Australia: droughts
Droughts are a recurrent and natural part of the Australian hydroclimate, with evidence of drought dating back thousands of years. However, our ability to monitor, attribute, forecast and manage drought is exposed as insufficient whenever a drought occurs. This paper summarises what is known about drought hazard, as opposed to the impacts of drought, in Australia and finds that, unlike other hydroclimatic hazards, we currently have very limited ability to tell when a drought will begin or end. Understanding, defining, monitoring, forecasting and managing drought is also complex due to the variety of temporal and spatial scales at which drought occurs and the diverse direct and indirect causes and consequences of drought. We argue that to improve understanding and management of drought, three key Climatic Change research challenges should be targeted: (1) defining and monitoring drought characteristics (i.e. frequency, start, duration, magnitude, and spatial extent) to remove confusion between drought causes, impacts and risks and better distinguish between drought, aridity, and water scarcity due to over-extractions; (2) documenting historical (instrumental and preinstrumental) variation in drought to better understand baseline drought characteristics, enable more rigorous identification and attribution of drought events or trends, inform/evaluate hydrological and climate modelling activities and give insights into possible future drought scenarios; (3) improving the prediction and projection of drought characteristics with seasonal to multidecadal lead times and including more realistic modelling of the multiple factors that cause (or contribute to) drought so that the impacts of natural variability and anthropogenic climate change are accounted for and the reliability of long-term drought projections increases.
Rainfall distribution of five landfalling tropical cyclones in the northwestern Australian region
Australian Meteorological and Oceanographic Journal, 2013
Rain gauge data, satellite IR brightness temperature and radar-estimated rain rate for five tropical cyclones from the 2005-06 to 2009-10 seasons that made landfall along the northwestern coast of Australia are analysed. It is the first time that the spatial rainfall distribution of landfalling tropical cyclones in the southern hemisphere has been systematically investigated. It is found that the distributions of rainfall are more concentrated in the right side of the track of the landfall tropical cyclones, which is the offshore flow position. Potential mechanisms responsible for this observed asymmetry in rainfall distribution are discussed. These include the tropical cyclone motion direction, deep-tropospheric vertical wind shear and land-sea contrast in surface properties. Topography is considered to have less effect since Western Australia is relatively flat. The rainfall maxima are found in the front and downshear quadrants for these tropical cyclones, which is consistent with previous studies. The changes in vertical wind shear when these tropical cyclones moved to the south are largely attributed to the prevailing environmental flow. Three numerical simulations are performed; one with a realistic land surface, one with all topography removed and one with all land removed. These simulations show that the land surface effects play an important role in determining the asymmetry in rainfall distribution, which explains why in some cases the observed maximum rainfall does not follow closely the vertical wind shear direction when making landfall.