Predicting dust and ground cover levels from antecedent rainfall

John Leys 1 ,2, Stephan Heidenreich1, Craig Strong3, Grant McTainsh2
1NSW Office of Environment and Heritage, Gunnedah, NSW, Australia, 2Griffith School of Environment, Griffith University, Brisbane, Queensland, Australia, 3Fenner School of Australian National University, Canberra, ACT, Australia

Wind erosion is an episodic phenomenon. Erosion activity varies from month to month and year to year; largely dependent upon climate and land management. The clearest evidence of the effect of climate on wind erosion is that dust levels are highest in drought years and lowest in wet years (see other papers at this conference). Natural Resource Management programs in Australia aim to improve land management practices and reduce accelerated wind erosion. But how will we know whether we are reducing accelerated wind erosion when climate is such a strong driver of erosion?

This paper presents a methodology for setting a benchmark for wind erosion and ground cover levels for a given rainfall regime, using dust (PM10 concentration > 25 g/m3measured by DustTrak) and ground cover levels (measured by MODIS satellite) over the 2005 to 2015 period in New South Wales. The aim of this work is to use the antecedent rainfall for a site to estimate if it is experiencing higher or lower exposed area and dust.

Our results show the maximum correlation between rainfall (mm in the preceding 3 to 36 months) and dust (hours per month with PM10 concentration > 25 g/m3), plus ground cover level (percentage of area with < 50% cover within 50km of the site, denoted ‘exposed area') and dust is the rainfall in the preceding 24 months depending on site and the season. For example, in stony landscapes around Tibooburra, NW NSW monthly dust in summer does not exceed 5 hours until about > 75% exposed area. In comparison, sandy farming areas like Euston only require about 5% exposed area to produce 5 hours of dust.

Using this methodology, the antecedent rainfall for Buronga in January 2014 was 443mm, which was 24% lower than the 10 year average antecedent rainfall of 581mm. However, despite the lower rainfall Buronga only had 4 hours of dust and 19% of exposed area which were 69% and 44% respectively lower than expected for the average antecedent rainfall. This indicates land condition upwind of Buronga was better in January 2014 compared to the longer term January average.