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 22 BCE–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 reduce 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.

Estimating surface melt in Antarctica from 1979 to 2022, using a statistically parameterized positive degree-day model

“…The two-sample Kolmogorov-Smirnov test (hereafter two-sample KS test) has been used in testing the significant difference between two non-Gaussian climatic distributions when parametric tests are inappropriate (e.g. Deo et al, 2009;Zheng et al, 2021). It has also been used as an alternative way to test the dissimilarity of climatic data as a validation of tests on statistical parameters such as the mean (Zheng et al, 2021).…”

2000 years of annual ice core data from Law Dome, East Antarctica

“…Therefore, as an alternative, we identify different epochs when we might expect similar distributions, specifically, periods of time covered by one of the ice cores where the average accumulation rate approximately the same in a different core making up the compilation but during a different period of time. Change-point analysis was performed on the cumulative summation (CUSUM) of the snow accumulation record to determine different epochs of approximately constant accumulation, a technique that has been used to detect changes in the Law Dome snowfall data by Zheng et al (2021). The CUSUM simply sums the data anomalies and identifies a step change in the underlying data through changes in the gradient of the CUSUM.…”

Caves provide early warning of unprecedented decrease in rainfall recharge of groundwater

“…Figure 5a,c compares the speleothem GL-S4 recharge d 18 O record with the Law Dome ice core accumulation-based rainfall reconstruction (see Fig. 1 for location) for southwest Western Australia 15,34 . The two records are in agreement in terms of the unprecedented nature for the last eight centuries of both the recent rainfall decrease depicted in the Law Dome record and the corresponding reduced rainfall recharge in the speleothem record.…”

“…Rainfall in southwest Australia is highly seasonal and falls in the cooler months, typically from May to October, owing to the seasonal migration of the Southern Hemisphere westerly winds. The region has experienced a prolonged decline in annual rainfall attributed to changes in Southern Hemisphere atmospheric circulation systems with a signi cant contribution from anthropogenic forcing 15,16 . In response to anthropogenic changes in ozone and then greenhouse gases 16 rainfall has decreased by 10-25% overall across the region since the 1960s 17 .…”