High Rainfall Zone

The zones were first defined by Stephen Hopper in his 1979 paper Biogeographical aspects of speciation in the southwest Australian flora.

However, following the publication of John Stanley Beard's phytogeographic 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 (IBRA) was published in the 1990s, Beard's regionalisation was adopted as the baseline for Western Australia.

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

The IBRA regions, with regions of the High Rainfall Zone shown in red.
Karri forest in the Warren region, part of the High Rainfall Zone. Rainfall in the Karri forests is the highest in the South West Botanic Province .