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1301.0 - Year Book Australia, 2002  
Previous ISSUE Released at 11:30 AM (CANBERRA TIME) 25/01/2002   
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Contents >> Geography and Climate >> Rainfall and other precipitation

Annual

The area of lowest rainfall is in the vicinity of Lake Eyre in South Australia, where the median annual rainfall is only about 100 mm. Another very low rainfall area is in Western Australia in the region of the Giles-Warburton Range, which has a median annual rainfall of about 150 mm. A vast region, extending from the west coast near Shark Bay across the interior of Western Australia and South Australia to south-west Queensland and north-west New South Wales, has a median annual rainfall of less than 200 mm. This region is not normally exposed to moist air masses for extended periods and rainfall is irregular, averaging only one or two days per month. However, in favourable synoptic situations, which occur infrequently over extensive parts of the region, up to 400 mm of rain may fall within a few days and cause widespread flooding.

The region with the highest median annual rainfall is the east coast of Queensland between Cairns and Cardwell, where Happy Valley has a median of 4,436 mm (43 years from 1956 to 2000 inclusive) and Babinda a median of 4,092 mm (84 years from 1911 to 2000 inclusive). The mountainous region of western Tasmania also has a high annual rainfall, with Lake Margaret having a median of 3,565 mm (76 years to 1987 inclusive).

The Snowy Mountains area in New South Wales also has a particularly high rainfall. While there are no gauges in the wettest area, on the western slopes above 1,800 metres elevation, runoff data suggest that the median annual rainfall in parts of this region exceeds 3,000 mm. Small pockets with median annual rainfall exceeding 2,500 mm also exist in the mountainous areas of north-east Victoria and some parts of the east coastal slopes. Map 1.5 shows average annual rainfall over the Australian continent.




1.5 AVERAGE ANNUAL RAINFALL






Seasonal

As outlined earlier, the rainfall pattern of Australia is strongly seasonal in character, with a winter rainfall regime in the south and a summer regime in the north.

The dominance of rainfall over other climatic elements in determining the growth of specific plants in Australia has led to the development of a climatic classification based on two main parameters, median annual rainfall and the incidence of seasonal rainfall.

Evaporation and the concept of rainfall effectiveness are taken into account to some extent in this classification, by assigning higher median annual rainfall limits to the summer zones than to the corresponding uniform and winter zones. The main features of the seasonal rainfall are:

  • marked wet summer (the 'Monsoon') and dry winter of northern Australia;
  • wet summer and relatively dry winter of south-eastern Queensland and north-eastern New South Wales;
  • uniform rainfall in south-eastern Australia - much of New South Wales, parts of eastern Victoria and southern Tasmania;
  • marked wet winter and dry summer of south-west Western Australia and, to a lesser extent, much of the remainder of southern Australia directly influenced by westerly circulation (sometimes called a 'Mediterranean' climate); and
  • arid area comprising about half the continent extending from the north-west coast of Western Australia across the interior and reaching the south coast at the head of the Great Australian Bight.

Figure 1.6 comprises individual graphs showing the monthly rainfall for all capital cities, as well as for Alice Springs and Davis Base in Antarctica.




Darwin shows the rainfall distribution pattern typical of the wet summer and dry winter seen in far northern Australia, and Brisbane the wet summer/relatively dry winter typical of southeastern Queensland. By contrast, Adelaide and Perth show the wet winter/dry summer pattern whereas Sydney, Melbourne, Canberra and Hobart show a relatively uniform pattern of rainfall throughout the year. Alice Springs shows a low rainfall pattern throughout the year typical of arid inland areas.

Precipitation at Davis Base is mainly as snow, but is measured as water after melting. The pattern reflects the very low precipitation levels on the Antarctic continent.

Rainday frequency

A rainday occurs when more than 0.2 mm of rain falls in 24 hours, usually from 9 a.m. to 9 a.m. the next day. The frequency of raindays exceeds 150 per year in much of Tasmania (with a maximum of over 250 in western Tasmania), southern Victoria, parts of the north Queensland coast and in the extreme south-west of Western Australia. Over most of the continent the frequency is less than 50 raindays per year. The area of low rainfall with high variability, extending from the north-west coast of Western Australia through the interior of the continent, has less than 25 raindays per year. In the high rainfall areas of northern Australia, the number of raindays is about 80 per year, but heavier falls occur in this region than in southern regions.

Rainfall intensity

The values in table 1.7 represent intensities over only small areas around the recording points because turbulence and exposure characteristics of the measuring gauge may vary over a distance of a few metres. The highest 24 hour (9 a.m. to 9 a.m.) falls are listed in table 1.8. Most of the very high 24 hour falls (above 700 mm) have occurred in the coastal strip of Queensland, where a tropical cyclone moving close to mountainous terrain provides ideal conditions for spectacular falls.

1.7 HIGHEST RAINFALL INTENSITIES
Period in hours
1
3
6
12
24
    Station
Period of record
Years of complete records
mm
mm
mm
mm
mm

    Adelaide
1897-2000
96
59
133
141
141
141
    Alice Springs
1951-1998
46
75
87
109
160
207
    Brisbane
1911-1998
87
99
142
182
266
327
    Broome
1948-2000
49
157
322
429
470
497
    Canberra
1937-2000
40
40
57
67
76
135
    Carnarvon
1956-2000
41
44
64
83
99
121
    Charleville
1953-1999
42
48
75
88
118
142
    Darwin (airport)
1953-2000
42
89
160
214
263
380
    Esperance
1963-1998
31
39
50
51
76
86
    Hobart
1911-1999
88
28
56
87
117
168
    Meekatharra
1953-2000
42
60
67
81
111
120
    Melbourne
1873-2000
107
75
91
91
97
130
    Mildura
1953-2000
42
53
60
68
68
91
    Perth
1946-1992
45
33
63
87
113
121
    Sydney
1913-2000
83
120
191
197
244
340
    Townsville
1953-1999
44
131
253
361
482
564

Source: Pluviograph records in Bureau of Meteorology archives.


1.8 HIGHEST DAILY RAINFALLS(a)
State/Territory
Amount (mm)
Date

New South Wales
Dorrigo (Myrtle Street)
809
21.2.1954
Cordeaux River
573
14.2.1898
Victoria
Tanybryn
375
22.3.1983
Club Terrace
285
24.6.1998
Queensland(b)
Beerwah (Crohamhurst)
907
3.2.1893
Finch Hatton PO
878
18.2.1958
South Australia
Motpena
273
14.3.1989
Nilpena
247
14.3.1989
Western Australia
Roebourne (Whim Creek)
747
3.4.1898
Roebuck Plains
568
6.1.1917
Tasmania
Cullenswood
352
22.3.1974
Mathinna
337
5.4.1929
Northern Territory
Roper Valley Station
545
15.4.1963
Angurugu (Groote Eylandt)
513
28.3.1953
Australian Capital Territory
Lambrigg
182
27.5.1925

(a) The standard daily rainfall period is 9 a.m. to 9 a.m.
(b) Bellenden Ker (Top Station) has, recorded a 48 hour total of 1,947 mm on 4-5 January 1979, including 960 mm from 3 p.m. on the 3rd to 3 p.m. on the 4th. No observation was made at 9 a.m. on the 4th.
    Source: Bureau of Meteorology.




    The highest annual rainfalls are listed by State/Territory in table 1.9.


    1.9 HIGHEST ANNUAL RAINFALLS
      State/Territory
    Station
    Year
    Amount (mm)

      NSW
    Tallowwood Point
    1950
    4,540
      Vic.
    Falls Creek SEC
    1956
    3,739
      Qld
    Bellenden Ker (Top Station)
    1979
    11,251
      SA
    Aldgate State School
    1917
    1,853
      WA
    Armadale (Jarrahdale PO)
    1917
    2,169
      Tas.
    Lake Margaret
    1948
    4,504
      NT
    Pirlangimpi
    1968
    2,762

    Source: Bureau of Meteorology.




    Thunderstorms and hail

    A thunderday at a given location is a calendar day on which thunder is heard at least once. The average annual number of thunderdays varies from 88 per year near Darwin to less than 10 per year over parts of the southern regions. Convectional processes during the summer wet season cause high thunderstorm incidence in northern Australia. The generally high incidence of thunderdays (40-60 annually) over the eastern upland areas is caused mainly by orographic uplift of moist air streams.

    Hail, mostly of small size (less than 10 mm diameter), occurs with winter-spring cold frontal activity in southern Australia. Summer thunderstorms, particularly over the uplands of eastern Australia, sometimes produce large hail (greater than 10 mm diameter). Large hail capable of piercing light-gauge galvanised iron occurs at irregular intervals and sometimes causes widespread damage.

    Snow

    Generally, snow covers much of the Australian Alps above 1,500 metres for varying periods from late autumn to early spring. Similarly, in Tasmania the mountains are covered fairly frequently above 1,000 metres in these seasons. The area, depth and duration are highly variable. Light snowfalls can occur in these areas at any time of year. In some years, snow falls in the altitude range of 500-1,000 metres. Snowfalls at levels below 500 metres are occasionally experienced in southern Australia, particularly in the foothill areas of Tasmania and Victoria, but falls are usually light and short lived. In some seasons, parts of the eastern uplands above 1,000 metres from Victoria to south-eastern Queensland have been covered with snow for several weeks. On sheltered slopes around Mt Kosciuszko (2,228 metres) small areas of snow may persist through summer, but there are no permanent snowfields.

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