Abstract
Abstract. Projections of sea level rise (SLR) will lead to increasing coastal impacts during extreme sea level events globally; however, there is significant uncertainty around short-term coastal sea level variability and the attendant frequency and severity of extreme sea level events. In this study, we investigate drivers of coastal sea level variability (including extremes) around Australia by means of historical conditions as well as future changes under a high greenhouse gas emissions scenario (RCP 8.5). To do this, a multi-decade hindcast simulation is validated against tide gauge data. The role of tide–surge interaction is assessed and found to have negligible effects on storm surge characteristic heights over most of the coastline. For future projections, 20-year-long simulations are carried out over the time periods 1981–1999 and 2081–2099 using atmospheric forcing from four CMIP5 climate models. Changes in extreme sea levels are apparent, but there are large inter-model differences. On the southern mainland coast all models simulated a southward movement of the subtropical ridge which led to a small reduction in sea level extremes in the hydrodynamic simulations. Sea level changes over the Gulf of Carpentaria in the north are largest and positive during austral summer in two out of the four models. In these models, changes to the northwest monsoon appear to be the cause of the sea level response. These simulations highlight a sensitivity of this semi-enclosed gulf to changes in large-scale dynamics in this region and indicate that further assessment of the potential changes to the northwest monsoon in a larger multi-model ensemble should be investigated, together with the northwest monsoon's effect on extreme sea levels.
Highlights
Extreme sea levels (ESLs) are a significant hazard for many low-lying coastal communities (Hanson et al, 2011; Nicholls et al, 2011), and with rising global mean sea level, extreme events are expected to rise (Menéndez and Woodworth, 2010)
In order to investigate characteristics of ESLs, a depthaveraged hydrodynamic model covering Australia was implemented at 5 km spatial resolution and baseline simulations carried out over the period 1981 to 2012 with hourly atmospheric and tidal forcing
Simulations of longer-term and short-term variations in sea level compare well with those measured at tide gauges, with differences largely reflecting the absence of baroclinic forcing in the model
Summary
Extreme sea levels (ESLs) are a significant hazard for many low-lying coastal communities (Hanson et al, 2011; Nicholls et al, 2011), and with rising global mean sea level, extreme events are expected to rise (Menéndez and Woodworth, 2010). For New York, Lin et al (2012) investigated the change in extreme sea levels arising from hurricanes over 2081–2100 relative to 1981–2000 in four GCMs run with the SRES mediumemission scenario by generating synthetic cyclones under the background conditions provided by the GCMs. Accounting for hurricane forcing only, results differed markedly between the four climate models ranging from overall increases to decreases in storm surge level. The present study assesses the performance of a mediumresolution barotropic hydrodynamic model for the Australian region to investigate extreme sea levels for the current climate and examines for the first time over the entire Australian coastline the potential changes in a future climate scenario in a four-member ensemble of climate model simulations.
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