Snow in southeast Australia

E. Linacre

9/'98

Snow cycles

It has been shown that the longterm mean annual maximum snow depth increases by about 70 cm for each 100 metres of elevation in the Snowy Mountains of southeastern Australia (Fig 10.20).

More snow tends to fall in alternate years (1). This biennial variation is presumably related to the Quasi-Biennial Oscillation (Section 12.3). Another rhythm was evident at several stations between 1956 - 1972: less snow falls each 3 to 4 years (2, 3), as can be seen in the annual snowfall record of Spencer's Creek (Fig 1). However this rhythm appears to be absent since 1972, and is only weak during 1935 - 1946.

Fig 1. The annual snowfall at Spencerís Creek in the Snowy Mountains of New South Wales. The dark bands refer to snowfall during the official skiing season, and the whole band to snowfall during the year. (Data from the Australian Bureau of Meteorology)

ENSO

To assess the effect of El Niño on snowfall at Spencer's Creek, we divide the annual mean SOI, as well as the annual snowfall, in two groups (El Niño vs. La Niña, and above-normal vs. below-normal, respectively). Then we perform a chi-squared test, shown in Table 1.

Table 1

El Niño

La Niña

above median snowfall

3

14

below median snowfall

7

11

The chi-squared value from this Table is 22, which implies a very high level of significance to the relationship between El Niño and snowfall - an El Niño means less-than-usual snowfall.

A more careful analysis shows a striking likelihood of deep snow during the winter before an El Niño event. Australia's snow season is June-September, whereas an El Niño usually peaks six months out-of-phase (December-March). During the pre-El-Niño winter, the upper level trough normally located south of Western Australia tends to move eastward, guiding frontal disturbances onto the Snowy Mountains.

 

Global warming

A correlation of the occurrence of snow with the temperatures locally at the time, and an estimate of the temperatures likely with global warming, allow inference of the latterís effect on snow cover. This consideration is important for skiing, tourism, water resources and hydro-electric power (4). Calculations based on best-case scenarios (a warming by 1K) indicate that by the year 2030 the snow season at places above 1700m is expected to last less than half as long as now.

 

References

(1) Budin, G.R. 1985. Interannual variability of Australian snowfall. Aust. Meteor. Mag., 33, 145-9.

(2) Linacre, E.T. & J.E. Hobbs 1977. The Australian Climatic Environment. (Jacaranda Wiley), p.94.

(3) Colquhoun, J.R. 1978. Snowfall in the New South Wales Snowy Mountains. Aust. Bur. Meteor. Tech. Report 25, 32pp.

(4) Whetton, P.H., M.R. Haylock & R. Galloway. Climate change and snow-cover duration in the Australian Alps. Climatic Change, 32, 447-79.