Extending and understanding the South West Western Australian rainfall record using a snowfall reconstruction from Law Dome, East Antarctica

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.

Geophysics reveals forest vulnerability to drought

“…Another key point is that the climate of the last 100 years may have been the wettest in the past 800 years (O'Donnell et al, 2021), thus potentially facilitating tree encroachment onto shallow soil areas. Now, during one of the driest periods in 2,000 years (Zheng et al, 2021), observed die-off likely reflects these trees reaching a critical threshold in shallow soils. Another way to think of this is that the critical soil thickness is increasing and expanding outwards from areas with shallow bedrock, due to the drying and warming.…”

“…While chronic drying may, in part, be a component of a much longer natural variability (O'Donnell et al, 2021), only two other droughts of similar duration and intensity have occurred in southwest Australia over the last 2,000 years (Zheng et al, 2021). With the future projections for southwestern Australia describing further climate drying and warming, we expect die‐off events will accelerate and expand to include more locations of forest in vulnerable, shallow soil areas (Hope et al, 2015).…”

Climatology of the Mount Brown South ice core site in East Antarctica: implications for the interpretation of a water isotope record

“…Previous work on the Law Dome ice core trace chemistry record has indicated that there are strong teleconnections between the southern Indian Ocean climate and Australian hydroclimate . The Law Dome snow accumulation record (Roberts et al, 2015) has been used to reconstruct rainfall across southwest Western Australia, indicating that current drying in the region is unusual but not unprecedented over the past 2000 years (Zheng et al, 2021;van Ommen and Morgan, 2010). Similarly, there is a strong correlation between concentrations of aerosol sea salts during summer snowfall at Law Dome with rainfall in eastern Australia (Vance et al, 2013(Vance et al, , 2015Udy et al, 2022).…”

Rainfall stable water isotope variability in coastal southwestern Western Australia and its relationship to climate on multiple timescales

“…There are several approaches for determining climate variability using paleoclimate records or reconstructions. Changes in rainfall have been inferred from distant measurements of snow accumulation (Zheng et al, 2021), which is possible because of an anticorrelation between SWWA May-October rainfall and snowfall at Law Dome, Antarctica (van Ommen & Morgan, 2010). Speleothem records, an in situ climate proxy, are found in caves which develop in Tamala Limestone (Geoscience Australia & Australian -3-manuscript submitted to JGR: Atmospheres Stratigraphy Commission, 2017), an eolian carbonate deposited in the Middle to Late Pleistocene, ∼10-250 ka before present (Smith et al, 2012).…”