Thornthwaite Moisture Index (TMI) is commonly used in climate zone classifications when designing residential slabs and footings on foundation soils with potential surface movements due to moisture changes. However in the current design guidelines – AS2870-2011, there is no specific guidance for the large land area of Western Australia. This paper has collected climate data in 39 town specific locations for 25 years (1988 ~ 2012). The TMI values were calculated using the method by Thornthwaite (1948). A climate zone map of Western Australia was produced based on the average TMI values of each town specific locations. The new climate zone map provided better predictions on the depth of soil suction change due to moisture change in Lake King, Ravensthorpe and Jerramungup with field data available.