Abstract
Abstract. South West Western Australia (SWWA) has experienced a prolonged reduction in rainfall in recent decades, with associated reductions in regional water supply and residential and agricultural impacts. The cause of the reduction has been widely considered but remains unclear. The relatively short length of the instrumental record limits long-term investigation. A previous proxy-based study used a statistically negative correlation between SWWA rainfall and snowfall from the Dome Summit South (DSS) ice core drilling site, Law Dome, East Antarctica, and concluded that the anomaly of recent decades is unprecedented over the ∼ 750-year period of the study (1250–2004 CE). Here, we extend the snow accumulation record to cover the period from 22 BCE to 2015 CE and derive a rainfall reconstruction over this extended period. This extended record confirms that the recent anomaly is unique in the period since 1250 CE and unusual over the full ∼ 2000-year period, with just two other earlier droughts of similar duration and intensity. The reconstruction shows that SWWA rainfall started to decrease around 1971 CE. Ensembles of climate model simulations are used to investigate the potential roles of natural variability and external climate drivers in explaining changes in SWWA rainfall. We find that anthropogenic greenhouse gases are likely to have contributed towards the SWWA rainfall drying trend after 1971 CE. However, natural variability may also have played a role in determining the timing and magnitude of the reduction in rainfall.
Highlights
South West Western Australia (SWWA) is characterised as a region with a Mediterranean-like climate (Yu and Neil, 1993; Siddique et al, 1999; Timbal et al, 2006)
We have found that the temporal stability of large-scale circulation over the mid-latitude Australasian and higher-latitude Law Dome regions is consistent, which is indicated by the correlation fields between Law Dome precipitation and mean sea level pressure in each member of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Mk3L OGSV ensemble (Fig. S5 in the Supplement)
We should be aware that the Law Dome– SWWA precipitation correlation is stronger during periods of enhanced meridional circulation, whereas it is weaker during periods of weaker meridional circulation
Summary
South West Western Australia (SWWA) is characterised as a region with a Mediterranean-like climate (Yu and Neil, 1993; Siddique et al, 1999; Timbal et al, 2006). Winter rainfall decreased by 15 %–20 % from the 1970s to the early 21st century (van Ommen and Morgan, 2010) This sizable winter rainfall reduction has contributed to decades of persistent drought since 1975 (Ansell et al, 2000; Cai and Cowan, 2006; Hope et al, 2006), causing water supply problems in WA (Pitman et al, 2004; Samuel et al, 2006). The SWWA rainfall reduction that occurred in the mid-20th century decreased the water supply to Perth by about 42 % (Pitman et al, 2004) This has required an additional investment of around USD 300 million to develop alternative water sources (Pitman et al, 2004). This long-term ongoing drought poses a potential threat to residential water supplies, industrial and agricultural production, and makes the study of this phenomenon and the determination of its driving factors urgent
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