The High Rainfall Zone is one of three biogeographic zones into which south west Western Australia

Western Australia

Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...

 is divided, the others being the Transitional Rainfall Zone

Transitional Rainfall Zone

The Transitional Rainfall Zone is one of three biogeographic zones into which south west Western Australia is divided, the others being the High Rainfall Zone and the Low Rainfall Zone...

 and the Low Rainfall Zone

Low Rainfall Zone

The Low Rainfall Zone is one of three biogeographic zones into which south west Western Australia is divided, the others being the High Rainfall Zone and the Transitional Rainfall Zone...

.

The zones were first defined by Stephen Hopper

Stephen Hopper

Stephen Donald Hopper is a Western Australian botanist, specialising in conservation biology and vascular plants. He has written eight books, and has over 200 publications to his name. He was Director of Kings Park in Perth for seven years, and CEO of the Botanic Gardens and Parks Authority for five...

 in his 1979 paper Biogeographical aspects of speciation in the southwest Australian flora. Initially they were defined in terms of rainfall, with the High Rainfall Zone being that part of the south west with annual rainfall of more than 800 millimetres (31 in). However, following the publication of John Stanley Beard

John Stanley Beard

John Stanley Beard was a British-born forester and ecologist who resided in Australia. While working with the Forestry Division in Trinidad and Tobago during the 1940s, Beard developed a system of forest classification for Tropical America and described the forests of Trinidad, Tobago, and the...

's phytogeographic

Phytogeography

Phytogeography , also called geobotany, is the branch of biogeography that is concerned with the geographic distribution of plant species...

 regionalisation of Western Australia in 1980, it was recognised that Hopper's zones could be defined as aggregates of Beard's botanic districts. The High Rainfall Zone was subsequently re-defined as equivalent to Beard's "Darling Botanical District", later renamed the "South-west Forest Region". When the Interim Biogeographic Regionalisation for Australia

Interim Biogeographic Regionalisation for Australia

The Interim Biogeographic Regionalisation for Australia is a biogeographic regionalisation of Australia developed by the Australian Government's Department of the Environment, Water, Heritage and the Arts...

 (IBRA) was published in the 1990s, Beard's regionalisation was adopted as the baseline for Western Australia. The South-west Forest Region was divided into three IBRA regions: Warren

Warren (biogeographic region)

Warren, also known as Karri Forest Region and the Jarrah-Karri forest and shrublands ecoregion, is a biogeographic region in southern Western Australia. Located in the southwest corner of Western Australia between Cape Naturaliste and Albany, it is bordered to the north and east by the Jarrah...

, Jarrah Forest

Jarrah Forest

Jarrah Forest is an Interim Biogeographic Regionalisation for Australia region in Western Australia.-Location and description:The ecoregion stands on the 300m high Yilgarn block inland plateau and includes wooded valleys such as those of Western Australia's Murray River and the Helena River near...

 and Swan Coastal Plain

Swan Coastal Plain

The Swan Coastal Plain in Western Australia is the geographic feature which contains the Swan River as it travels west to the Indian Ocean. The coastal plain continues well beyond the boundaries of the Swan River and its tributaries, as a geological and biological zone, one of Western Australia's...

. Hence the High Rainfall Zone is now defined as the aggregate of these three IBRA regions.