The Peel-Harvey basin has a Mediterranean climate with hot dry summers and cool wet winters. Approximately 90% of annual precipitation falls between April and October.
The area of highest rainfall is on the scarp and annual rainfall is approximately 900 mm per year over the coastal plain and increases up to 1300 mm per year over the scarp. Rainfall declines east of the scarp to around 450 mm per year in the eastern most part of the catchment.
Around half the annual inflow to the estuary is received in July and August and two thirds is received from June to October. The majority of streams receive minimal flow between December and April with the majority of this being derived from groundwater (WRC, 2000 and Bussemaker, 2004).