Engineers Australia

Evaluation of changes of the Thornthwaite Moisture Index in Victoria

Jie Li and Xi Sun


Climate change has become one of the most pressing environmental concerns and the greatest challenges to global infrastructure today. It has been demonstrated by many researchers that Victoria along with other Australian States and Territories has been experiencing a drying trend over the last several decades. Numerous lightly-loaded residential buildings constructed on expansive soils are subjected to distortions arising from differential ground movements caused by seasonal soil moisture changes. The climatic parameter, Thornthwaite Moisture Index (TMI) has been widely used by geotechnical engineers and practitioners as a means of classifying climatic zones and estimating the depth of design soil suction changes. The main aim of this paper is to evaluate changes of TMI index in Victoria in the past 60 years. Long-term (1954-2013) meteorological data from 70 weather stations across Victoria were employed to develop TMI isopleth maps for the three 20-year periods (i.e. 1954-1973, 1974-1993 and 1994-2013). The methodology and equations employed for TMI computation are presented and a worked example is provided as well.