Synoptic climatology of extreme precipitation in alpine Australia

Abstract

ABSTRACT:Extreme precipitation over the eastern Australia can be significantly enhanced by topographic interaction with the westerly flow. These extreme events can cause severe flooding, damage and disruption to human activities, yet in some areas they are also an invaluable source of water and snow. In this study, we use rain gauge and snowfall accumulation data to investigate connections between extreme rain and snow in alpine Australia and the large-scale climate. These data have been divided into three geographical locations: the west of the mountains, the ridgeline and the east of the mountains in order to explore the nature of precipitation in each region. The results confirm previous synoptic patterns found earlier in the literature for the western slopes (namely embedded and cutoff lows), and add new insights into the different processes conducive to extreme precipitation on the eastern side of the ranges, which we find to be mostly associated with a blocking structure connected to polar latitudes. Interestingly, our analyses suggests that while a La Niña pattern accompanied by enhanced meridional sea surface temperature (SST) gradients over mid-latitudes is associated with extreme events in the western and high regions, the extreme precipitation composites for the eastern region are associated with a SST pattern that resembles the predominant signal associated with global warming in the Australian region. We hypothesize that while the western and high regions rely on SST gradients, which enhance the westerly jet, the extreme events over the eastern side rely on blocking patterns (anomalous easterlies), which are at least partially responding to the global SST warming with the respective shift of the westerlies to the south. These results help explain why the precipitation over the western side of the Alps is declining more rapidly than the total precipitation observed on the eastern side.

Trends in synoptic circulation and precipitation in the Snowy Mountains region, Australia, in the period 1958–2012

“…Hoy et al 2014;Newton et al 2014a, b;Bettolli et al 2010;Stahl et al 2006). Theobald et al (2015) presents a novel, automated approach to classifying year-around synoptic systems across SEA, building upon previous studies which largely focussed on cool-season precipitation, ; Pook et al 2006;Wright 1989, Fiddes et al 2014. In addition to the widely studied cold front and closed low weather systems, Theobald et al (2015) found a strong emphasis on tropical moisture pathways from oceans to the north-east and north-west of Australia for delivering precipitation to the Snowy Mountains region.…”

A Synoptic Classification of Inflow-Generating Precipitation in the Snowy Mountains, Australia

“…The cool-season synoptic circulation over various regions of SEA has been well studied (e.g., Wright 1989;Pook et al 2006;Landvogt et al 2008;Risbey et al 2009;Gallant et al 2012), although few studies relate specifically to the Snowy Mountains area (Colquhoun 1978;Chubb et al 2011;Fiddes et al 2015). These studies commonly report cool-season precipitation declines.…”

The influence of climate drivers on the Australian snow season

“…There are no comparable snow depth data sets for the Victorian mountains, with the best available data (Fiddes et al, 2014a) starting in the 1980s, and hence this study will focus on the New South Wales data. While Victorian seasonal snow depths would be expected to be closely correlated with those in New South Wales, extension of these results to Victoria should be done with some caution, particularly as the weather systems that produce the majority of snowfall may differ across the ranges.…”

“…Nicholls (2005) identified a 10% decline in annual maximum snow depth between 1962 and 2002, with the largest decline in spring (40%), while Davis (2013) identified that the average annual maximum snow depths were 15% lower than the 1961-1990 average during 2001-2010. This decline has occurred despite no significant changes in the average precipitation at nearby stations (Davis 2013) or the frequency of extreme precipitation events (Fiddes et al 2014a), and appears primarily related to enhanced warming over the alpine region. The larger trends in spring come as a result of this season being more marginal, with the warming trend bringing forward the shift of snow accumulation to snow loss.…”