Where is the cool change?

It is not unusual in summer for southeastern Australia to experience a run of temperatures above 100°F (37.8°C), especially inland. However, two heat-waves stand out.

The period between 13 and 20 January 1908 remains the most sustained hot spell in Melbourne’s history. For five consecutive days (16th-20th) the temperature exceeded 40°C (with 39.9°C on the 15th), peaking at 44.2°C on the 17th. There was little wind until the approach of a cool change on the last day - just hot, still conditions, with no relief from sea breezes. In an era without refrigeration, air-conditioning or effective sanitation, and with polite dress being thick, three-piece suits and long skirts, the effects were traumatic. Ice-works worked flat out to try to keep up with demand. At the beaches the question of mixed bathing was settled as men and women mixed freely in the water. Each day brought deaths from the heat, among people of all ages. Bushfires were not a feature of this heat wave, because of the light winds, and preceding heavy rain in late December; however there were fires in the Otways and South Gippsland, with some people killed and many made homeless.

The heat wave in January 1939 was notable for its longevity and extremely high temperatures. On 9 January the temperature at Kyancutta reached 49.3°C, the highest recorded in South Australia at that time. Adelaide's all time record of 46.1°C was reached on the 12th; Melbourne’s (45.6°C) on the 13th (after 44.7°C on the 10th); and Sydney’s (45.3°C) on the 14th (with Manly reaching 47.2°C and Richmond 47.8°C). Temperatures in northern New South Wales approached 48°C on the 15th. In western NSW, Menindee registered 49.7°C. In Melbourne the heat in 1908 was more consistent than during the 1939 heatwave, when weak cool changes brought temporary relief. However the heat inland in 1939 was more intense and longer-lasting: at Mildura the temperature exceeded 37.8°C on each of the first 14 days of January, and at the peak of the heatwave, averaged 45.6°C from 7-14 January. More than 400 deaths in Victoria were attributed to the heat.

Temperatures at Melbourne and Mildura during the severe 1939 heatwave. Note the intervening cooler days in southern Victoria due to the passage of weak cool changes, compared with the unrelenting heat inland, where cooler air failed to penetrate.

Lighter clothing was worn in 1939 compared with 1908, and men would at least take their coats off. However home refrigerators were rare and air-conditioned buildings were unknown. Relief was sought at the beaches and baths: there were by then no inhibitions about mixed bathing.

Unlike 1908, the hot spells in 1939 were accompanied by strong northerly winds, and followed a very dry six months. This led to the disastrous Black Friday bushfires in Victoria.