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Chapter 3 - Changes in Climate Extremes and their Impacts on the Natural Physical Environment
- from Section III
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- By Sonia I. Seneviratne, Neville Nicholls, David Easterling, Clare M. Goodess, Shinjiro Kanae, James Kossin, Yali Luo, Jose Marengo, Kathleen McInnes, Mohammad Rahimi, Markus Reichstein, Asgeir Sorteberg, Carolina Vera, Xuebin Zhang, Matilde Rusticucci, Vladimir Semenov, Lisa V. Alexander, Simon Allen, Gerardo Benito, Tereza Cavazos, John Clague, Declan Conway, Paul M. Della-Marta, Markus Gerber, Sunling Gong, B. N. Goswami, Mark Hemer, Christian Huggel, Bart van den Hurk, Viatcheslav V. Kharin, Akio Kitoh, Albert M.G. Klein Tank, Guilong Li, Simon Mason, William McGuire, Geert Jan van Oldenborgh, Boris Orlowsky, Sharon Smith, Wassila Thiaw, Adonis Velegrakis, Pascal Yiou, Tingjun Zhang, Tianjun Zhou, Francis W. Zwiers
- Edited by Christopher B. Field, Vicente Barros, Thomas F. Stocker, Qin Dahe
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- Book:
- Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation
- Published online:
- 05 August 2012
- Print publication:
- 28 May 2012, pp 109-230
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Summary
Executive Summary
This chapter addresses changes in weather and climate events relevant to extreme impacts and disasters. An extreme (weather or climate) event is generally defined as the occurrence of a value of a weather or climate variable above (or below) a threshold value near the upper (or lower) ends (‘tails’) of the range of observed values of the variable. Some climate extremes (e.g., droughts, floods) may be the result of an accumulation of weather or climate events that are, individually, not extreme themselves (though their accumulation is extreme). As well, weather or climate events, even if not extreme in a statistical sense, can still lead to extreme conditions or impacts, either by crossing a critical threshold in a social, ecological, or physical system, or by occurring simultaneously with other events. A weather system such as a tropical cyclone can have an extreme impact, depending on where and when it approaches landfall, even if the specific cyclone is not extreme relative to other tropical cyclones. Conversely, not all extremes necessarily lead to serious impacts. [3.1]
Many weather and climate extremes are the result of natural climate variability (including phenomena such as El Niño), and natural decadal or multi-decadal variations in the climate provide the backdrop for anthropogenic climate changes. Even if there were no anthropogenic changes in climate, a wide variety of natural weather and climate extremes would still occur. [3.1]
A changing climate leads to changes in the frequency, intensity, spatial extent, duration, and timing of weather and climate extremes, and can result in unprecedented extremes. Changes in extremes can also be directly related to changes in mean climate, because mean future conditions in some variables are projected to lie within the tails of present-day conditions. Nevertheless, changes in extremes of a climate or weather variable are not always related in a simple way to changes in the mean of the same variable, and in some cases can be of opposite sign to a change in the mean of the variable. Changes in phenomena such as the El Nino-Southern Oscillation or monsoons could affect the frequency and intensity of extremes in several regions simultaneously. [3.1]
The impact of eastern Australian cut-off lows on coastal sea levels
- Kathleen L McInnes, Graeme D Hubbert
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- Journal:
- Meteorological Applications / Volume 8 / Issue 2 / June 2001
- Published online by Cambridge University Press:
- 19 June 2001, pp. 229-244
- Print publication:
- June 2001
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- Article
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Cut-off lows that develop off the east coast of Australia are a major cause of elevated coastal sea levels in this region. Their duration often exceeds a day and the combination of elevated sea levels with the high rainfall that commonly accompanies these events means that coastal flooding can be a major hazard. The processes contributing to higher-than-normal sea levels are a combination of storm surge and breaking wave setup. Three events are modelled using an atmospheric model, storm surge model and wave setup model. The storm surges resulting from the depressions are found to explain between one-third and one-half of the measured sea-level residuals at the coast and are shown to develop in a regime of coast-parallel winds that produce onshore Ekman transport. The timing of the storm surges are well captured in two of the events in which the atmospheric depressions are of broad spatial scale and well simulated by the atmospheric model. However, a poor simulation by the atmospheric model of the location of the third low, which is of smaller spatial scale, results in an inaccurate timing of the onset of the surge. The wave setup model produces sea levels at the coast that are around 11% of the incident rms wave heights. The total modelled sea-level residual, obtained by adding the modelled wave setup to the storm surge, is qualitatively similar to the measured sea-level residual. However, the modelled values are higher, especially at Sydney where the tide gauge is situated in a sheltered harbour location. In such sheltered locations, it is expected that some attenuation of the wave setup would occur and suggests that sea levels on the open coast could be considerably higher during such events.