Fewer large waves projected for eastern Australia due to decreasing storminess

Abstract

Extratropical cyclones are the main generators of the strong winds that cause large ocean waves in temperate regions of the world. The severity of the winds associated with these storms is poorly represented by the coarse resolution of current global climate models (GCMs), making it challenging to produce projections of the future climate of large waves. Wind data from GCMs can be downscaled in resolution using dynamical methods, resulting in a successful reproduction of the mean wave climate, but a suboptimal reproduction of the storm wave climate 1 . Projections of large wave occurrence can also be produced using statistical downscaling methods, although such methods have previously been applied only to three or less GCMs 2,3 , preventing a robust assessment of confidence in projections based on variation between models. Consequently, considerable uncertainty remains in projections of the future storm wave climate. Here we apply a statistical diagnostic of large wave occurrence in eastern Australia to 18 di erent GCMs, allowing model variations to be examined in greater detail than previously possible. Results are remarkably consistent between di erent GCMs, allowing anthropogenic influences to be clearly demonstrated, with fewer days with large waves expected to occur in eastern Australia due to increasing greenhouse gas concentrations.

Information for Australian impact and adaptation planning in response to sea-level rise

“…An additional consequence of the projected southward movement of the STR is a projected decrease in wave heights and changes in the wave climate on the NSW coast (Hemer et al, 2013a,b;Dowdy et al, 2014). O'Grady et al (2015) has shown that the change in both wind-driven currents and waves in south-eastern Australia may lead to complex seasonal changes in longshore sediment transport with subsequent impacts on the near shore region.…”

“…leading to a reduction in storm tides) along the south coast with small increases occurring in eastern Bass Strait and parts of Tasmania, mostly in winter and spring. The changes were consistent with the southward movement of the subtropical ridge (STR, Kent et al, 2013) bringing weaker winds to the southern mainland coast but stronger winds and higher variability over Tasmania.An additional consequence of the projected southward movement of the STR is a projected decrease in wave heights and changes in the wave climate on the NSW coast (Hemer et al, 2013a,b;Dowdy et al, 2014). O'Grady et al (2015) has shown that the change in both wind-driven currents and waves in south-eastern Australia may lead to complex seasonal changes in longshore sediment transport with subsequent impacts on the near shore region.…”

Using large-scale diagnostic quantities to investigate change in East Coast Lows

“…Major climate drivers such as the El Nino-Southern Oscillation and the Indian Ocean Dipole have substantially weaker correlations with rainfall in this region than elsewhere in eastern Australia (Murphy and Timbal 2008;Timbal 2010). Recent research suggests that East Coast Lows (ECLs), also known as east coast cyclones, are a dominant driver of climate for the region (Dowdy et al 2014), that strongly influences extreme rainfall along the eastern seaboard (Imielska et al 2012;Pepler and Coutts-Smith 2012).…”

Maps, laws and planning policy: Working with biophysical and spatial uncertainty in the case of sea level rise

“…The response of coastal systems to changing boundary conditions including rising sea-levels, increased storminess or modified rates of sediment supply will greatly vary in space and time based on local conditions (Fitzgerald et al, 2008). For example, there is clear evidence that the eastern coast of Australia will be subject to fewer but larger storms and associated larger waves, which will influence the distribution and magnitude of local beach erosion (Dowdy et al, 2014). Further, changes in the rate of natural sediment supply or human-induced sediment compaction have resulted in increased coastal vulnerability.…”