Update on timber decay hazard map of Australia

Abstract

Timber durability in outdoor applications is strongly influenced by climatic conditions such as rainfall, temperature, and humidity, which affect the activity of biodeteriogens. Existing Australian service life prediction models rely on empirical climate relationships, based on rainfall, temperature and dry days, which were drawn upon to formulate hazard map zones that were then set with expert guidance. The current hazard maps developed in the Forest & Wood Products Australia Design for Durability (FWPA DfD) project divide Australia into four broad hazard zones, that were convenient to use and represented the best approach at the time. Areas that experience quite different decay hazards, however, may fall within the same zone, and locations either side of zone boundaries can appear to have abrupt changes in decay potential. This limits the accuracy of the maps and calculations that rely on zone factors, and highlights the need for a more detailed, location-specific approach drawing on information technology resources now available. This paper presents decay hazard maps for Australia that were developed using multiple approaches, followed by a comparative overview and discussion of their outcomes. The analysis began with the Scheffer Climate Index (SCI), a widely used indicator of above-ground decay potential based on mean monthly temperature and rainfall. The report then discusses hazard maps that were produced using the Department of Primary Industries Durability Index (DI), which incorporates drying potential through vapour pressure deficit and percent wet days (factors particularly relevant to Australian climates). Finally, in-ground hazard maps based on equations developed in the FWPA DfD project were presented, alongside an assessment of the limitations of applying the FWPA DfD equation to above-ground conditions and the proposal of a new approach. Each hazard mapping approach demonstrated strengths and limitations. For example, the SCI may underrepresent decay potential in southern Western Australia and in regions near, but not adjacent to the coast, while the DI provides better representation in WA but may overestimate decay hazards in Tasmania. The published FWPA DfD hazard maps categorise Australia into four broad zones. In this paper, a higher-resolution hazard map based on FWPA DfD formulae for in-ground applications was produced. For above-ground environments, due to complexity in the half-hourly rainfall data, maps were generated using a generalised linear model (GLM) that incorporated variables such as mean annual temperature, average annual vapour pressure deficit, and average daily rainfall. Enhanced maps can be made publicly accessible once verification and validation are completed. With modern data-visualisation tools, an online platform incorporating heat maps and location-specific "pin-drop" queries will provide an effective and user-friendly means of determining climate hazard values for any selected Australian location.