Southwestern Australia, July 1926

Rainfall in southwestern Australia is strongly concentrated in the winter months, and thus flooding tends to be mostly a winter phenomenon. There are exceptions, such as in February 1955 and January 1982, when ex-tropical cyclones dumped hundreds of millimetres over the area and triggered severe flooding in local rivers. However most flooding, at least in the wetter areas of southwestern Australia, occurs when a series of strong winter storms produce prolonged heavy rainfall. In general these floods cause less damage than their counterparts in the east, and loss of life is rare.

The winter of 1926 was exceptional for its persistent and sometimes heavy rainfall over southwestern Australia. Following a rather wet April, the first half of May was virtually dry. The rains returned with a vengeance just after mid-month, and from then until September, seemed to be unrelenting. At Collie, the 111-day period from 18 May to 5 September had only six rain-free days. In mid-July, with the ground by now saturated., a low pressure complex became established to the south of Western Australia. This generated frequent heavy rains and fierce westerly gales: in some coastal areas there was significant wind damage as well as flooding. Over the week ending 22 July rainfall totals were widely in excess of 100mm, and even some of the drier inland wheatbelt centres such as Northam and Beverley registered 80 to 90mm of rain.

Widespread flooding resulted. Extensive areas of the southwest were under water, with large portions of the towns of Northam, York, Beverley and Collie inundated. Flooding was also severe in the Upper Swan–Guildford and South Perth areas around the Swan River, and in and around Bunbury. Flooding extended as far east as Lake Grace, an uncommon event in winter. The huge volume of water destroyed several bridges - including the Fremantle railway bridge on 22 July, which collapsed soon after a passenger train from Perth had made the crossing!

The events of 1926 were a noteworthy episode from a time when flooding in the southwest was more common than it is today. This reflects the fact that, between the turn of the century and the 1960s, the southwest was distinctly wetter than it has been over the past 30 years. However it is worth noting that floods were also less common in the 1880s and 1890s, whereas in the 1860s and 1870s there were a number of severe events. Long-term climate fluctuations of this kind can sometimes lull people into false perceptions about the degree of risk from flooding.

On the other hand, the decrease in rainfall over southwestern Australia during the late 20th century is generating concern for those people managing water resources for the area’s growing population, and for those involved in water-sensitive activities such as agriculture and environmental conservation.