Natural Environment Murchison

Climate

The climate of the Murchison is semi-arid to arid, with hot summers and mild winters. Temperatures are highest between January and February, during this time inland average temperatures generally exceed 37°C. Due to sea breezes, coastal temperatures are kept well below those inland. Average winter temperatures average below 18°C in. The average annual rainfall of the Murchison is between 190 mm to 250 mm Rainfall in the Murchison is unreliable. Most of the rainfall occurs in winter and most years there is a dry period of 4 to 6 months.

Rivers

The watercourses of the Murchison are ephemeral, meaning the rivers dry up for at least part of the year. The major catchment of the region is the Murchison River catchment.The Murchison River Basin has a total area of approximately 91,000 km2 and discharges into the Indian Ocean at Kalbarri. It includes tributaries of the Sandford, Roderick, Yalgar and Hope rivers.

Wetlands

Although much of the subregion’s surface water is ephemeral, there are a number of permanent pools and soaks that survive the summer as wetlands. Wetlands of national significance in the Murchison subregion are Hamelin Pool, Murchison River (lower reaches), Anneen Lake (Lake Nannine), Breberle Lake, Lake Ballard, Lake Barlee, Lake Marmion and Wooleen Lake.

Murchison_2012_4

Murchison River in low flow. Photo taken by Melanie Strang

The climate of the Murchison is semi-arid to arid, with hot summers and mild winters. Temperatures are highest between January and February, during this time inland average temperatures generally exceed 37°C. Due to sea breezes, coastal temperatures are kept well below those inland. Average winter temperatures average below 18°C in. The average annual rainfall of the Murchison is between 190 mm to 250 mm Rainfall in the Murchison is unreliable. Most of the rainfall occurs in winter and most years there is a dry period of 4 to 6 months.

Rivers

The watercourses of the Murchison are ephemeral, meaning the rivers dry up for at least part of the year. The major catchment of the region is the Murchison River catchment.The Murchison River Basin has a total area of approximately 91,000 km2 and discharges into the Indian Ocean at Kalbarri. It includes tributaries of the Sandford, Roderick, Yalgar and Hope rivers.

Wetlands

Although much of the subregion’s surface water is ephemeral, there are a number of permanent pools and soaks that survive the summer as wetlands. Wetlands of national significance in the Murchison subregion are Hamelin Pool, Murchison River (lower reaches), Anneen Lake (Lake Nannine), Breberle Lake, Lake Ballard, Lake Barlee, Lake Marmion and Wooleen Lake.

Coastline

The major area of coastline in the Murchison subregion is the Shark Bay World Heritage Area. The Shark Bay World Heritage Area is Australia’s largest enclosed marine embayment. It covers an area more than 2.2 million hectares and has a coastline greater than 1,500 km long.

Flora and Fauna

The biodiversity of the Murchison is rich and varied across extensive terrestrial ecosystems. The Shark Bay World Heritage Area is an exceptional marine and coastal zone.

This subregion contains 18 species of Declared Rare Flora (DRF), 95 Priority One Flora, 49 Priority Two Flora, 142 Priority Three Flora and 26 Priority Four Flora. There are no threatened ecological communities known to occur here.

Vegetation

Vegetation is predominantly chenopod and Acacia shrublands and woodlands, however many other vegetation types can be found within this region. The Murchison subregion is essentially Western Australia’s mulga region.

Vegetation within this subregion is closely associated with the climate, geology and soils. Mulga low woodlands are supported by areas of outcropping rock with skeletal soils. On calcareous soils there are hummock grasslands and saltbush shrublands while on saline alluvium areas there are samphire (Halosarcia sp.) low shrubland. To the east of the subregion, mallee-mulga parkland over hummock grassland is supported by red sand plains. The lake margins in the Murchison are dominated by lignum (Muehlenbaeckia cunninghamii) and low open woodland of river red gum (Eucalyptus camuldulensis).

IBRA Subregions

The Murchison contains two IBRA sub-regions: Murchison and Yalgoo. To read more about IBRA subregions, and to access the Australian Government's detailed descriptions of each, see the IBRA subregions page.