The Climate and Weather of Australia/Chapter 10

by Henry Ambrose Hunt, Griffith Taylor, E. T. Quayle

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X(a).—RAINFALL IN THE WEST AUSTRALIAN GOLD-FIELDS.

In the dry region of Western Australia—for the most part with a rainfall of less than 10 inches per year—are three important centres of settlement. In the north is the Pilbara Gold-field, in the centre the Murchison Gold-field, and in the south the Coolgardie Gold-field. Kalgoorlie has a population of over 17,000 inhabitants, while some £112,000,000 have been won by miners from the gold-fields of Western Australia.

A special study of the rainfall of this area is justified by its economic importance and by its interest as a region which has been settled in defiance of physical control.

Frequency of Rain Storms.

An analysis has been made of the conditions governing the rainfall in the inland portion of Western Australia during the period July, 1909—July, 1912.

The rain storms are classified in three groups—

Coolgardie (Southern Gold-field).

Peak Hill (Central Gold-field).

Pilbara (North-west Gold-field).

In most cases Coolgardie participated in rains from the north which affected the other two, but the contrary is by no means true—rains moving from the south rarely reaching Peak Hill and never Pilbara.

The number of rain storms affecting the fields in this period is shown in the following table (for three years):—

—	Summer.	Autumn.	Winter.	Spring.	Total.
	December, January, February.	March, April, May.	June, July, August.	September, October, November.
Pilbara	10	9	7	1	27
Peak Hill	13	9	18	8	48
Coolgardie	12	17	35	18	82
Individual Storms[1]	21	24	39	26	..

The table shows that Coolgardie lies in the winter rain region, and that Peak Hill gets its infrequent rains both in winter and summer, while Pilbara, so far as frequency is concerned, has a slight summer maximum and a more characteristic spring minimum.

Direction of Rain Winds.

The wind directions tabulated refer to the dominant winds over the whole rain area ("smear" is used for such local rain) due to one particular storm or set of controls.

The rain winds affecting the dry interior are chiefly from the north to north-east octant, veering to the north-west in part in the colder months. But the south-west and south winds also exercise a beneficial effect, especially in the colder months:—

Fig. 75.

Summer.		Autumn.		Winter.		Spring.
N.E. = 8 N.  = 2	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$ 10	N.W. = 7 N.  = 3 N.E. = 6	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$ 16	N.  = 15 N.W. =  4 N.E. =  4	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$ 23	N.E. = 10 S.W. = 10 S.   =  4	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$ 14
S.  = 6 S.W. = 2	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$ 8	S.W. = 5		S.W. = 11
Others 3		Others 3		Others 4		Others 3

Pressure Systems and their Distribution.

The conditions leading to the fall of rain in the interior of Western Australia are by no means always of the same type. The most striking feature shown by the analysis is the persistence of one type throughout a season in one year which may not occur in the same season next year. For instance, in January and February, 1911, there was a greater distance between the low (over Condon) and the high to the south-east (south of Mt. Gambier, &c.) than usual. In June and July, 1910, and 1912, the high covered most of Eastern Australia, while the low off Albany led to rains over the gold-fields. In these two months during the intermediate year 1911, there seemed a tendency for the succeeding high to appear sooner off North-west Cape and control the situation. The same "habit" is shown in other months, but not to the extent of obliterating the characteristic features of the distribution of highs and lows each month.

There is perhaps no need to emphasize the fact that, in an immense area like Australia, each climatological division exhibits as diverse features as does, for instance, the whole of the British Isles.

In January, the rain smears extend usually over the three gold-fields. They occur nearly always when a low lies off North-west Cape—the high being to the south-east, either over the Bight or further east. The wind is generally from the north—east, but if the southern high is rather to the west then south winds also bring rain to the fields.

In February, the conditions are much the same. The rains in the north (Pilbara) usually accompany north winds in front of the low, and those in the south south or south-east winds in front of the high. There is a strong tendency for the low to "sit" over the north of the high in this month, when rain is probable.

In March—The above conditions obtain also in March, but in addition rains with south winds occur sometimes with a low south of the Leeuwin and a high advancing on Geraldton (vide 2nd March, 1912). The southern cyclonic eddies are now moving north and affect the continent.

In April, the second type of rain-bringer is prevalent, i.e., a low south of Leeuwin and a high approaching Geraldton. Winds are northerly first, and then southerly as the low advances. Coolgardie rains are due usually to the latter winds.

In May, the favorable condition for rain appears to be when two highs lie rather near together ("A" over South-eastern Australia and "B" off Geraldton), with a low just south of Cape Leeuwin. The winds are northerly and the rain smear chiefly in the south.

In June, conditions are much the same. The first high lies over Central and East Australia, the second approaches North-west Cape, while the low lies off Cape Leeuwin. The accompanying winds (north-east and then south-west) both lead to rains, though in this month the southern winds affecting Coolgardie region are of increasing importance.

Variation in the position of the preceding high does not seem to be of such importance as gradient. For instance, in June, 1912, the gold-fields experienced a dry spell, although the conditions as stated above recurred about once a week as usual:—

June, 1912.

Date.	Rain.	Highs—Velocity.	Gradient.	Path.
3rd	No rain on fields, but in south-west	300 (1,200 m. in 4 days)	Gradient small = 28 4/10 700 m.)	Centre moved E. from Adelaide to Sydney
10th	Rain over Cool- gardie	450 (900 m. in 2 days)	(4/10 in 500 m. Gradient = 40	Centre moved due E. to Grafton
17th	No rain on fields. Rain in SW. cor- ner only	450 (900 m. in 2 days)	Gradient= 33 (4/10 in 600 m. but rapidly lessen- ing	Centre moved S.E. Coolgardie to Robe
28th	Rain over Cool- gardie	350 (350 m. in 1 day)	(5/10 in 400m.) = 62	Centre moved S.E. from Adelaide to Bass Straits

This summary shows that increased gradient (implying stronger winds) is apparently the most favorable factor in supplying Coolgardie with rain; for the velocity and path varied without effect.

In July, the lows are slightly further north than in June, and the preceding high covers Central and Eastern Australia. The winds are usually from the north drawn into the front of the low. Rains due to south-west winds in the rear of the low are also common, especially in the south-west corner.

In August.—In 1909 and 1910 the rains were generally due to northerly winds in front of a low. In 1911, they were nearly all due to south-west winds from the rear of the low, the high following close after. The lows appeared to have a somewhat more southern "habit" throughout the month of August in 1911.

In September, a tendency for the low to run up between the two highs is noticeable. If the latter are close together so that the gradient is steep there would seem to be better chances for rain. Thus in 1911 in this month there were six high-pressure systems in evidence, but only three with somewhat steeper gradients led to rain.

In October, rains are rare in the gold-fields region, and there seems to be no very favorable arrangement of the pressure conditions. Both south-west and north-east winds bring rain, chiefly to the south. Thunderstorms may occur over the fields.

In November, a low usually "broods" over Central Australia, sometimes forming a true "monsoonal" tongue from the north. Conditions are very unfavorable for rain over the gold-fields. Thunderstorms may, however, occur and give local rain.

In December, the same conditions obtain as in November. Thunderstorms are not uncommon.

Summary of Position of Eddies from July, 1909, to July, 1912.

—	Highs.					Lows.
	Summer.		Autumn.	Winter.	Spring.	Summer.	Autumn.	Winter.	Spring.
Off Perth and Cape Leeuwin	9		8	9	6	1	5	15	1
S. of Esperance and in Bight	6		3	..	5	..	12	16	8
Off N.W. Cape and Cossack	2		5	5	7	13	1	..	4
Over E. Australia	..		5	19	9	..	..	..	..
Others	2		1	3	..	1	2	3	7
									tongues

Average figures for the monthly rainfall in the gold-fields have already been given in a preceding section.

X.(b).—FLOOD RAINS IN AUSTRALIA.

These phenomena occur at infrequent intervals in various regions of the continent, causing considerable damage to stock, bridges, roads, &c., in our sparsely-populated and pastoral territories. Brief summaries of the meteorological conditions accompanying the following occurrences will be of interest:—

(1) 1909, August, floods in South-Eastern Australia.

(2) 1910, January, floods on the Darling.

(3) The heavy rains of Queensland.

(4) The heavy rains of Northern West Australia.

(1) The Cyclonic Storm of 16th—21st August, 1909 (South-East Australia).^[2]

During the month of August every station in South-Eastern Australia recorded above the normal fall, except the coastal fringe from the Gippsland Lakes northward. In South Australia, where the mean fall in the settled districts ranged up to more than double the normal, and in Victoria, where the greater part of the State had over twice the normal amount, this month will rank as one of the wettest on record.

The rains were not only abnormally heavy, but well distributed through the month, though the rain producing storm systems were actually few in number (only four). They moved slowly, developed well inland, and the path followed by their centres was further north than usual, all passing over or very little south of Tasmania. Each of these disturbances was marked by cold, wet, and stormy weather, but the storm tendencies of the month culminated on the 19th in torrential rains and fierce thunderstorms, which caused one of the most disastrous floods Victoria has ever experienced.

The graphs appended to this book include a series of the 9 am. weather charts (see Figs. 77—82) during the passage of an extensive storm system of cyclonic energy which traversed the whole of sub-tropical Australia, from Cape Leeuwin to Gabo, between the 16th and 21st of the month, and was the main factor in the development of the exceptional storm rains and floods now under review. Moving over an area already saturated by a period of almost constant rain—for scarcely a day passed during the previous fortnight without widespread and at times heavy downpours, especially in southern and South-Eastern Australia—its effect was most disastrous, and creeks and rivers, already swollen, were turned into raging torrents which overflowed their banks, and spread ruin and desolation over the surrounding country. The map of the 16th shows the advent of the disturbance, which had rapidly advanced from the southern Indian Ocean during the previous 24 hours, in the extreme west of the continent. Its centre was then off the south-west coast of Western Australia, the embracing isobars being somewhat irregular in shape and gradients moderate, and its rain area covered the whole of that State south from the tropic, with heavy falls near the coast (Perth, 213 points; and 23 other stations from 1 to 2 inches). Next morning (17th) the centre occupied much the same position, the gradients had lessened and the isobars indicated the tendencies to form a doubleheaded depression, and another general, though less heavy, rain was registered south from the latitude of Geraldton.

On the 18th the gradient had still further declined, but the low area had assumed a definite "Λ" shape, with its apex intruding well inland to much lower latitudes than on the previous day. This carried the rain, which was again general, on to the tropic, though the area of greatest precipitation was still in the south-west (Perth, 141; and nine others over 1 inch). The chart of the 19th shows that the storm area had made a distinct surge eastward to the South Australian coast, with an extension of its isobars into still lower latitudes, and a general intensification and steepening of the gradients. A new high-pressure area of considerable energy had developed over Western Australia, which stimulated the circulation in the rear of the disturbance, while the stationary anticyclone on the east coast and the Tasman Sea maintained velocities in the advancing side. Very disturbed

FLOOD RAINS IN SOUTH—EAST AUSTRALIA.

Note.—The parts coloured dark blue represent rivers and districts more or less flooded—the lower portions during August, 1909 the upper portions during January 1910. Light blue shade indicates over 5” of rainfall in August, 1909.

Fig. 76.

Flood Rains
Rain Areas Hatched

weather was anticipated, as this type of chart (19th) showing a deep cyclonic depression, wedged in between two energetic anticyclones, with isobars running approximately north and south, is a very favorable forerunner of widespread rains on the Australian continent, and the subsequent conditions more than realized these anticipations. Up to the 18th the disturbance was marked by heavy rains, though only moderate winds, but on that day it began to develop cyclonic and electrical energy, and its subsequent career was accompanied by most violent atmospheric commotion. On the night of the 18th violent thunderstorms, with fierce squalls and heavy rain, broke over the far north-western and western areas of South Australia, and rapidly swept across the State into Victoria, rain falling at 153 stations in South Australia up to 9 a.m. next morning (19th), of which 52 registered between ½ and 1 inch, and 55 over 1 inch (maximum, 168, at Streaky Bay, on the west coast), and at 135 stations in Victoria, of which 26 recorded between ½ and 1 inch, and 21 others over 1 inch (maximum, Dimboola, 183). The rain area had also widened considerably, for light rain was still falling in Western Australia, and commencing in Tasmania.

By the 20th the storm had reached its greatest intensity, its cyclonic centre being clearly shown to the south of Victoria and near the north-west corner of Tasmania (barometer at Stanley, 28.96 inches), with exceptionally steep gradients. Along the south-east coast of South Australia the previous night the weather was extremely wild, with winds of hurricane violence and exceptionally low barometers, and rain fell throughout the whole of South Australia, Victoria, Tasmania, and New South Wales, and extended into the south-west and south of Queensland, being recorded at 155 stations in South Australia, of which 56 registered from ½ to 1 inch, and 8 over 1 inch (maximum, Uraidla, 169); at 156 stations in Victoria, of which 55 had between ½ and 1 inch, 56 from 1 to 2 inches, and 18 others over 2 inches (maximum, Kyneton, 325); at 31 stations in Tasmania, 9 being from ½ to 1 inch, 9 from 1 to 2 inches, and 3 over 2 inches (maximum, Burnie, 271); at 140 stations in New South Wales, of which 46 records were between ½ and 1 inch, and 10 over 1 inch (maximum, Tumbarumbah, 181); and light falls at 44 stations in Queensland. The last chart of the series shows that the disturbance had passed eastwards to the Tasman Sea and become of a simple "Antarctic!" type while high pressures had become established over the continent. The isobaric distribution is of the ordinary winter type and fine weather returns.

A reference to the rain smears plotted with the isobars on Figs. 77-82 shows that it was in Victoria that the greatest overlap of the daily falls occurred. Hence, the floods were greatest in the rivers draining the Victorian highlands (see Fig. 76).

The series of heavy rains, accompanied by violent and prolonged thunderstorms, which set in over the western parts of this State in the early morning of the 19th August, gradually extended eastwards during the day, and was responsible for phenomenal floods in almost all the rivers in the western half of the State. These rains appear to have been at their greatest intensity along two parallel lines, one joining Warracknabeal and Queenscliff, the other Inglewood and Kyneton, and these give pretty nearly the direction in which the storm clouds were observed to be moving during the fifteen to twenty hours within which all the rain fell. East of Kyneton, the rains lost their extraordinary character, but falls of over 1 inch were still the rule in all except the plains or country of relatively low level stretching from Echuca to Wodonga, and including Benalla, while in the more mountainous country the falls were generally between 1 and 2 inches. In Gippsland, owing to the mountain barrier to the north and west, the rainfall was generally insignificant, and actually nil around and east of the Lakes. The heaviest totals, above 4 inches, were received along a narrow strip of high country following the crest of the Dividing Range westward from Kyneton, and probably including the Pyrenees.

A brief summary of the heights reached in the various tributaries affected is appended:—

River.	Town.	Height on Staff, etc.	Remarks.
Murray	Echuca	32 ft. 2 in.	Twice exceeded (1867 and 1870)
Goulburn	Shepparton	33 ft.	Only twice exceeded (by a few inches) since 1881
Wimmera	Jeparit	16 ft.
Avoca	Charlton		6 inches above 1870 flood, and 4 feet above any others
Loddon	Laanecoorie	36 ft.
Campaspe	Rochester	28 ft. 11 in.
Murrumbidgee	Narrandera	26 ft. 6 in.	Below the great flood of 1853.

(2) The Floods in the Darling Tributaries, January, 1910.^[3]

The disastrous flood in the Upper Darling tributaries, consequent on the abnormally heavy rains on the north—western plains and slopes of New South Wales, as well as those on the Darling Downs of Queensland, is, from a meteorological stand-point, one of the most interesting events during 1910. These exceptionally heavy, continuous rains were caused by the joint action of an anti-cyclonic area over the southern half and the monsoonal depression operating in the northern half of the continent. The movements and subsequent development in intensity of this monsoonal tongue were meteorologically interesting. It was first truly delineated on the 7th January, as far south as Wilcannia, but on the 8th it had retreated to the south-west corner of Queensland. On the 10th, it protruded as far south and east as Albury, but withdrew the next day to the Queensland border, without, however, making any easterly progress. The high pressure had now intensified, though there had actually been a divergence of the isobars, due, no doubt, to the vapour-laden condition of the atmosphere. Within the next few days the tongue had expanded considerably, stretching as far south as Deniliquin, and on the 15th had intensified to such an extent as to form what is technically known as a closed curve depression. It was during this period that the heaviest falls were recorded. The Namoi Basin experienced particularly heavy falls on the 14th and 15th, and the average total rainfall for fifteen stations in that area from the 11th to the 15th inclusive was 8.63 inches, several places recording more than 12 inches of rain for that period. Copious falls occurred in the catchment area of the Condamine River, in Queensland, the average total for 26 stations from the 10th to the 17th inclusive being 4.71 inches. Cambooya and Dalby, both in this area, registered 10.17 and 9.68 respectively. The MacIntyre Basin was also unusually favoured, the average total for six stations, from the 10th to the 17th, being 7.13

WEATHER CHARTS.-FLOODS OF JANUARY, 1910.

inches—Goondiwindi, 9.11; Umbercollie, 9.90; and Bingarra, 19.44 being the heaviest falls recorded. The enormous amount of water which fell over these districts, covering approximately 86,000 square miles, may be roughly estimated at 31,687,000,000 tons, or 7,100,000,000,000 gallons, the average total fall for the 77 rain recording stations from the 11th to the 15th inclusive being 5.7 inches. The very heavy falls in the Namoi Basin on the 14th and 15th, reaching as high as 6½ inches for 24 hours in some places, succeeding the moderately heavy falls of several days before, caused the flood in this tributary to rise higher than that in any other river. The water spread itself over the country for miles in every direction, devastating the surrounding districts and wreaking incalculable destruction of property, as well as causing some loss of life. Almost all the towns along its banks were inundated, Tamworth, Gunnedah, Manilla, Boggabri, Narrabri, and Wee Waa suffering particularly. Our observers report that this flood is the greatest since 1864, the water being 6 feet deep in the streets of Tamworth, while at Narrabri the river attained the greatest height ever known. The Gwydir and Barwon also reached record heights, both Moree and Brewarrina being partly submerged. Bourke appeared to be threatened with destruction. If the Queensland rivers, Condamine, Balonne, and Culgoa, which drain a large area and enter the Darling between Bourke and Brewarrina, had contributed their quota to the already flooded stream, Bourke must inevitably have been swept away; but, fortunately, this was not the case, as these waters did not reach Bourke till some days later. All the creeks and smaller water-courses were likewise in a flooded state, and the waters covered an extensive area. The thirsty plains would absorb an immense quantity of water on this account, as the contour of the country is conducive to such a result. Thousands of head of stock were drowned, and, generally speaking, the amount of damage was enormous.

(3) Heavy Rains of Queensland.

The Queensland coast is characterized by occasional very heavy downpours. These are almost entirely confined to the summer months, as the following table (for storms giving over 10 inches during 23 years, 1887-1909) clearly indicates:—

Month.	January.	February.	March.	April.	May.	June.	July.	August.	September.	October.	November.	December.
Number	104	42	92	24	1	9	1	1	2	0	2	26
Per cent.	33	14	31	8	..	3	..	..	1	..	1	9

The Map (Fig. 89) shows that a few large downpours have also occurred in the gulf country around Burketown. With these exceptions, only one other inland fall was recorded—at Monkira, in the far south-west. Here, over 11 inches fell on 1st February, 1906, the average annual fall (21 years) being 9 inches. This station forms a notable example of the necessity of long periods to arrive at a true mean. In 1900 the annual rainfall was 2½ inches, and in 1906 it was 29 inches.

The following table gives the most important recent occurrences of these downpours in Queensland:—

Amount	Station.	Locality.	Date.	Year.
35.71	Crohamhurst	45 miles north-west of Brisbane	31st January	1893
26.20	Buderim	North of Brisbane	11th January	1898
25.12	The Hollow	Mackay	23rd February	1888
23.33	Macnade	Townsville	6th January	1901
23.07	Yeppon	Rockhampton	31st January	1893
22.17	Dungeness	Cardwell	16th March	1893
21.53	Mooloolah	North of Brisbane	13th March	1892
22.22	Innisfail	South of Cairns	29th December	1903
21.00	Nambour	South of Gympie	9th January	1898
20.08	Yandina	South of Gympie	1st February	1893
20.05	Yeppoon	Rockhampton	31st January	1893
19.55	Crohamhurst	45 miles north-west of Brisbane	9th January	1898
19.55	Howard	Maryborough	15th January	1905
19.20	Townsville	North Coast	24th January	1892
18.24	Cardwell	North Coast	18th March	1904
18.31	Brisbane	South Coast	21st January	1887
18.07	Thornborough	Near Cairns	20th April	1903
18.20	Anglesey	Gympie	26th December	1909
18.05	Yeppoon	Rockhampton	8th January	1898
17.40	Bloomsbury	Brisbane region	14th February	1893
17.95	Mundoolun	South of Brisbane	21st January	1887
17.75	Palmwoods	Brisbane	25th December	1909

These phenomenal rains are seen to be most abundant between Cairns and Cardwell. The great number recorded in the Brisbane district is largely due to the fact that here the rain-gauges are well distributed and fairly numerous, which is not the case in the less settled regions of Queensland.

(4) Flood Rains in Western Australia.

Perhaps the most striking region in Australia for examples of abnormal rainfall is in the far north-west in Western Australia (Fig. 90). Here the 10-in. annual isohyet passes near many stations which have recorded more than that amount in one rainstorm, though of course falls of this type are few and far between. Some of the heavier falls are given in this table, where a comparison with the average annual amount should be found of interest in many cases:—

Inches.	Station.	Position.	Date.	Year.	Average Annual Rainfall.	Number of Years.
36.49	Whim Creek	Near Cossack	2nd and 3rd April	1898	19.87	14
27.06	Whim Creek	Near Cossack	20th and 21st March	1899	19.87	14
24.18	Thangoo	Near Broome	17th and 19th February	1896	22.61	17
21.42	Yeeda	Near Derby	28th, 29th, and 30th December	1898	23.66	21
20.82	Wyndham	Long., 128°, lat., 15° S.	11th, 12th, and 13th January	1903	27.27	25
20.40	Balla	Near Cossack	20th and 21st March	1899	17.98	6
20.23	Derby	King Sound	29th and 30th December	1898	26.38	26
20.12	Cossack	Long, 117°, lat., 21° S.	15th and 16th April	1900	12.01	30
17.47	Obagama	Near Derby	16th, 17th, and 18th February	1896	34.48	16
15.25	Boodarie	North-east of Cossack	3rd and 4th January	1894	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$ 12.49	24
14.53	Boodarie	North-east of Cossack	21st March	1899

1. N.B.—Many of these "Individual Storms" affected two centres.
2. Bulletin No. 3—Commonwealth Bureau of Meteorology.
3. Australian Monthly Weather Report, January 1910, Commonwealth Bureau of Meteorology.