Short-Term Thornthwaite Moisture Index (TMI) for Australian Climate

Soil-atmospheric boundary interaction is vital for the geotechnical design as the soil behaviour is moisture dependent, especially for expansive soils. Understanding the soil-atmospheric boundary interaction and the effect of climate change can be important for ensuring the resilience of geotechnical infrastructure. Thornthwaite Moisture Index (TMI) has been adopted in many geotechnical designs to account for the climate-induced moisture variations within the soil. The average TMI deducted from long-term climate data (continuous 25+ years) is often correlated with the design parameters such as the suction change depth and hence the characteristic surface movement. The behaviour of many structures can be influenced by shorter-term weather events and a shorter-term TMI may present a better correlation in such scenarios. However, high variability and the non-stationary character of a short-term TMI can be hindrances for any real-life application. This study assesses 1, 3, 6 monthly, and yearly TMI values estimated from 30 years of climate data. The result showed a significant difference exists between these monthly and annual average TMI values. This highlights the significance of incorporating short-term climate events and integrating climate change into geotechnical structures for the betterment of the built environment through safer, more resilient, and sustainable design.