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McInnes K.L.,CSIRO | Walsh K.J.E.,University of Melbourne | Hoeke R.K.,CSIRO | O'Grady J.G.,CSIRO | And 2 more authors.
Global and Planetary Change | Year: 2014

Extreme sea level events due to tropical cyclone storm surge combined with astronomical tide (storm tides) severely impact Pacific Island communities and these impacts are expected to increase with projected sea level rise. However, these sea level extremes are not well characterised by available tide gauge records owing to the low frequency of occurrence of tropical cyclones, the sparse array of tide gauges and the short time frame over which many gauges in this region have been operating. In this study, a combined statistical/dynamical method for estimating storm tide risk is presented. Tropical cyclones in the Fiji region over the period 1969-2007 are characterised in a statistical model that represents cyclone frequency, intensity and movement. The statistical model is then used to develop a population of "synthetic" cyclones that provide boundary conditions to a hydrodynamic storm surge and tidal model. This Monte-Carlo method is applied to the coasts of the Fiji archipelago. It is found that storm tide risk is higher on the northwest coasts of both the southern and northern main islands Viti Levu and Vanua Levu, respectively. Modelling suggests that there is a greater tendency for higher storm surges to occur on southwest Viti Levu under El Niño and La Niña years compared with average years, but elsewhere on Viti Levu and Vanua Levu, there is a tendency for slightly lower storm surges in La Niña years. Imposing perturbations to the cyclone statistical model that represent projected tropical cyclone changes in intensity and frequency for mid to late 21st Century, leads to storm tide return period curves that are steeper such that sea levels associated with return periods of 200. years or more become higher, those with return periods of 50. years and less become lower and the 1-in-100. year heights are little changed. Projected changes in sea level are found to make the largest contribution to increased extreme sea level risk. © 2014 Elsevier B.V. Source

McInnes K.L.,CSIRO | Hoeke R.K.,CSIRO | Walsh K.J.E.,University of Melbourne | O'Grady J.G.,CSIRO | Hubbert G.D.,Global Environmental Modelling Systems
Natural Hazards | Year: 2016

Tropical cyclone-induced storm surges cause damaging impacts in coastal regions. The present study uses a stochastic cyclone modelling approach to evaluate the likelihoods of storm tides, the combination of storm surges and astronomical tides, for Samoa. Cyclones that occurred in the vicinity of Samoa from 1969 to 2009 are used to build a stochastic tropical cyclone data set, and an analytic cyclone model and hydrodynamic model are used to model storm tides under average, La Niña and El Niño cyclone and sea level conditions for present climate conditions as well as cyclone and sea level conditions relevant for 2055, and storm tide return periods are estimated. We find that extreme storm tides exhibit relatively modest variation around the coastline of Samoa owing to the uniform width of the shelf surrounding the coastlines of two main islands of Savai’i and Upolu. The frequency of cyclones and hence storm tides during El Niño conditions is similar to the frequency for all seasons, but is considerably lower in La Niña conditions. For the future, tropical cyclones are assumed to undergo decreased frequency and increased intensity. This is found to lower the storm tide height for return periods <100 years and increase it for return periods greater than about 200 years. Sea level rise is shown to have a larger influence on storm tides than future changes to tropical cyclones. Considering the aggregated probabilities of storm tides occurring at the national scale, we find that the likelihood of a storm tide occurring that locally exceeds a 1-in-100-year level (i.e. an event with a 1 % annual exceedance probability) has a 6 % probability of occurring somewhere along the entire coastline of Samoa. Such information may be useful for those involved in coastal management and disaster response for which there may be a need to consider the overall likelihood that a nation may have to respond to such a disaster. © 2015, Springer Science+Business Media Dordrecht. Source

Smith G.A.,Swinburne University of Technology | Babanin A.V.,Swinburne University of Technology | Riedel P.,Coastal Engineering Solutions | Young I.R.,Swinburne University of Technology | And 2 more authors.
Coastal Engineering | Year: 2011

The significant loss of wave energy due to seabed interaction in finite depths is a known effect and bottom friction terms are used in the wave models to account for this dissipation. In this paper, a new bottom-interaction function is tested by means of the SWAN model, based on measurements at two field sites, Lake George and Lakes Entrance, both in Australia. The function accounts for dependence of the friction on the formation process of bottom ripples and on the grain size of the sediment. The overall improvement of the model prediction both for the wave height and wave period is demonstrated. © 2010. Source

Mcinnes K.L.,CSIRO | Macadam I.,University of New South Wales | Hubbert G.,Global Environmental Modelling Systems | O'Grady J.,CSIRO
International Journal of Climatology | Year: 2013

Current climate 1-in-100-year storm tide heights along the coast of Victoria, southeast Australia were estimated by combining probabilities of storm surge and tide heights determined from hydrodynamic modelling. For this return period, levels lie between 1 and 2 m above mean sea level along much of the coastline. Future climate 1-in-100-year storm tide heights were estimated by adding high-end estimates of future sea-level rise from recent literature. The effect of climate change through consistent wind-speed increases was also examined and it was found that, for the late 21st Century, the contribution of wind-speed increase to the increases in extreme storm surge heights is considerably smaller, by a factor of more than 2, than the contribution of sea-level rise. A computationally inexpensive approach to assessing current and future vulnerability to coastal inundation due to sea-level extremes is then demonstrated for the Victorian coast. A simple inundation algorithm was used with high-resolution terrestrial elevation data from a Light Detection and Ranging (LiDAR) survey of the Victorian coast to evaluate the potential vulnerability of nine coastal regions to inundation by current and future climate 1-in-100-year storm tides. The response of different regions varied from exhibiting proportional increases in inundation to sea-level rise to nonlinear responses, where the exceedance of critical sea-level thresholds led to large stepwise increases in land area or number of land parcels affected by inundation. These responses were a function of both coastal topography and the spatial density of land parcels. The low computational cost of the methodology permits different time horizons and uncertainties in future climate change to be considered using a scenario-based approach and is therefore useful in assessing options for adaptation to climate change. © 2011 Royal Meteorological Society. Source

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