BAMOS Winter Vol 34 No.2 July 2021 | Page 11

Article

BAMOS July 2021
11
What do the changes mean for coastal impacts ?
The increase in westerly wind regime ECLs from 1995 – 2019 has occurred further away from the coast but further north than 1970 – 1994 ( Figure 2 ).
For the ECLs that form in an easterly wind regime , they have also formed further east away from the coast in the far north but at the same time their development has extended further south ( Figure 3 ).
These shifts in ECL development southwards are consistent with well-known findings from climate models that the midlatitude westerly winds in general will shift poleward as a result of global warming ( e . g ., Perren et al . 2020 ; Yin 2005 ).
The counter-intuitive regional changes found here of systems developing from the westerlies shifting north and eastwards relate to the structure of air flow in the upper atmosphere and are the subject of ongoing research . The immediate impact of easterly developed systems shifting southward implies more ECL events on the far southern half of the NSW coast with rain , strong winds and large waves . However , counteracting that , the increase in westerly developed systems on the south coast of NSW does not imply increased rainfall ( except in the far south from an easterly component onto the far south coast ) because the resulting west to southwest winds further north are dry .
On otherwise fine days , coastal impacts for large waves that have developed well east of the coast are a threat to coastal recreational fishers , in particular . Large , long fetch swell waves from ECLs in the east and south can sometimes interrupt otherwise benign coastal sea conditions as it did at Port Kembla in early 2021 .
However , as global warming increases and the mid-latitude westerly winds contract further poleward , those ECLs that develop in a westerly wind regime are likely to shift further poleward or decrease in frequency if the mean flow flattens , as suggested in recent research ( Dowdy et al . 2014 ).
This article is a research summary of a paper recently published in Climate : Changes in Frequency and Location of East Coast Low Pressure Systems Affecting Southeast Australia .
References
Australian Bureau of Meteorology and CSIRO . State of the Climate 2020 . 2020 . P . 24 . Available online : http :// www . bom . gov . au / state-of-the-climate /. Accessed 07 May 2021 .
Dowdy , A ., Mills , G ., Timbal , B ., et al . 2014 . Fewer large waves projected for eastern Australia due to decreasing storminess . Nature Clim . Change 4 , 283 – 286 . https :// doi . org / 10.1038 / nclimate2142
Godfrey , J . S ., Cresswell , G . R ., Golding , T . J ., and Pearce , A . F . 1980 . The separation of the East Australian Current . J . Phys . Oceanogr ., 10 , 430 – 439 . https :// doi . org / 10.1175 / 1520-0485 ( 1980 ) 010 < 0430 : TSOTEA > 2.0 . CO ; 2
Perren , B . B ., Hodgson , D . A ., Roberts , S . J ., et al . 2020 . Southward migration of the Southern Hemisphere westerly winds corresponds with warming climate over centennial timescales . Commun . Earth Environ . 1 , 58 . https :// doi . org / 10.1038 / s43247-020-00059-6
Sanders , F . and Gyakum , J . R ., 1980 . Synoptic-Dynamic Climatology of the “ Bomb ”. Mon . Wea . Rev ., 108 , 1589-1606 . https :// doi . org / 10.1175 / 1520- 0493 ( 1980 ) 108 < 1589 : SDCOT > 2.0 . CO ; 2
Speer , M . S ., Wiles , P . and Pepler . A . 2009 . Low pressure systems of the New South Wales coast and associated hazardous weather : establishment of a database . Aust . Met . Mag ., 2009 ; 58 , 29 – 39 , http :// doi . org / 10.22499 / 2.5801.004
Speer , M ., Leslie , L ., Hartigan , J . and MacNamara , S . 2021 . Changes in Frequency and Location of East Coast Low Pressure Systems Affecting Southeast Australia . Climate 9 , 44 . https :// doi . org / 10.3390 / cli9030044
Yin , J . H . 2005 . A consistent poleward shift of the storm tracks in simulations of 21st century climate . Geophys . Res . Lett ., 32 , L18701 . https :// doi . org / 10.1029 / 2005GL023684
Figure 2 . L – R : The increase in westerly wind regime ECLs from 1970 – 1994 to
1995 – 2019 .
Figure 3 . L – R : The increase in easterly wind regime ECLs from 1970 –
1994 to 1995 – 2019 .