Climate

The southwest coastal area of WA has a Mediterranean climate and was originally heavily forested, including large stands of the karri, one of the tallest trees in the world. This agricultural region of WA is in the top nine terrestrial habitats for terrestrial biodiversity, with a higher proportion of endemic species than most other equivalent regions. Thanks to the offshore Leeuwin Current the area numbers in the top six regions for marine biodiversity, containing the most southerly coral reefs in the world.

Average annual in rainfall in WA varies from 300 millimetres (12 in) at the edge of the Wheatbelt region to 1,400 millimetres (55 in) in the wettest areas near Northcliffe , WA , but in the months of November to March evaporation exceeds rainfall, and it is generally very dry. Plants must be adapted to this as well as the extreme poverty of all soils. A major reduction in winter rainfall has been observed since the mid-1970s, with a greater number of extreme rainfall events in the summer months.

The central four-fifths of the state is semiarid or desert and is lightly inhabited with the only significant activity being mining. Annual rainfall averages 200–250 millimetres (8–10 in), most of which occurs in sporadic torrential falls related to cyclone events in summer months.

An exception to this is the northern tropical regions of WA. The Kimberley , WA has an extremely hot monsoonal climate with average annual rainfall ranging from 500 to 1,500 millimetres (20–60 in), but there is a very long almost rainless season from April to November. Eighty-five percent of the state's runoff occurs in the Kimberley Western Australia , but because it occurs in violent floods and because of the insurmountable poverty of the generally shallow soils, the only development has taken place along the Ord River.

Occurrence of snow in the state is rare, and typically only in the Stirling Range near Albany WA , as it is the only mountain range far enough south and with sufficient elevation. More rarely, snow can fall on the nearby Porongurup Range . Snow outside these areas is a major event; it usually occurs in hilly areas of South Western Australia. The most widespread low-level snow occurred on 26 June 1956 when snow was reported in the Perth Hills WA, as far north as Wongan Hills and as far east as Salmon Gums. However, even in the Stirling Range, snowfalls rarely exceed 5 cm (2 in) and rarely settle for more than one day.

The highest observed maximum temperature of 50.5 °C (122.9 °F) was recorded at Mardie, Pilbara, 61.6 kilometres (38.3 mi) from Barrow Island on 19 February 1998 . The lowest minimum temperature recorded was -7.2 °C (19.0 °F) at Eyre Bird Observatory on 17 August 2008 .