Western Australia: an environment for migration?

The state of Western Australia (WA) occupies approximately one-third of the Australian continent. It consists principally of a gently undulating plateau 300–600 m above sea level; there are no outstanding mountain ranges. Three broad climatic zones are recognised (Fig. 9.1): a tropical region in the north, with 90% of annual rainfall (500–1200 mm) falling between November and March (summer); a Mediterranean region in the southwest with 80% of annual rainfall (400–1200 mm) falling between April and September (autumn, winter and early spring); and an arid (desert and semidesert) zone, occupying the great majority of the state's land area, in which rainfall averages less than 300 mm per year. Cropping is almost completely confined to the Mediterranean region, and occurs principally in a broad band towards its boundary with the arid zone. Within the vast arid zone, rainfall occurs mainly during summer in the north, during both summer and winter in the centre, and during winter in the southwest. It is non-seasonal in the southeast (Fig. 9.1b). Rain usually falls on only a few days each year and drought conditions can persist for months or even several years. Temperatures are generally high, with mean monthly maxima exceeding 37 °C in the hottest 3–5 months. Average annual evaporation is more than ten times the rainfall.