Estimating the wind erosion potential of east Australian droughts over 120 years.

Katherine Parsons 1, Craig Strong2, Tadhg O'Loingsigh1, Harry Butler3, Grant McTainsh1
1Griffith School of Environment, Griffith University, Brisbane, QLD, Australia, 2Fenner School of Environment & Society, ANU College of Medicine, Biology & Environment, The Australian National University, Canberra, ACT, Australia, 3School of Agricultural, Computational & Environmental Sciences, Faculty of Health Engineering & Sciences, University of Southern Queensland, Toowoomba, QLD, Australia

Wind erosion has long been recognised to be driven by the susceptibility of soil to erosion (soil erodibility) and the erosive nature of the wind (wind erosivity). Numerous authors have examined the factors influencing soil erodibility, including; soil moisture, soil structure, vegetation and biological crusting, and erosivity factors such as wind strength and synoptic-scale systems. While numerous studies have developed values of potential wind erosion (or wind erosion risk) based on these factors or broadly recognised drought as influencing wind erosion activity, very few studies have attempted to quantify the potential wind erosion of different drought periods.

This paper examines the wind erosion potential of eight drought periods over 120 years in eastern Australia. Data from 22 consolidated Bureau of Meteorology stations are used to measure the severity of eight drought periods (and within them numerous drought episodes). The wind erosion potential of each drought period is then quantified in terms of erodibility (vegetation cover and type) and erosivity (wind speed).

The Standardized Precipitation Index (SPI) is used to measure drought period severity; by summation of drought episode intensities. The Climate Aridity Vegetation Index (CAVI) is used to estimate vegetation cover; with decile values used to provide historically context. Vegetation type is described using the National Vegetation Information System (NVIS). Wind erosivity is quantified using the proportion of average wind speed to maximum wind gust as deciles. These three measures; drought severity, vegetation and wind speed, are then combined to provide an overall estimate of the wind erosion potential for each station and drought period.

It was found that the wind erosion potential of the Millennium Drought (2001-2009) was highest, followed by the Federation Drought (1895-1903) and Long El Niņo Drought (1991-1995). The remaining drought periods had overall lower wind erosion potential values; with some isolated high to very high values specific to individual stations.

The Federation Drought (1895-1903) was the most severe drought, followed by the World War II Drought (1939-1945) and Millennium Drought (2001-2009). For vegetation cover, the Federation Drought (1895-1903) the lowest vegetation cover, followed by the 1918-20 Drought, the 1914-15 Drought and El Niņo Drought. Vegetation types responded differently to drought periods. The Federation Drought (1895-1903) was the worst drought for grasslands, the Millennium Drought (2001-2009) worst for eucalypt and other forests, and the Federation Drought (1895-1903) worst for saltbushes. The Long El Niņo Drought (1991-1995) had the highest wind speeds, followed by the 60s Drought (1965-1968) and the Millennium Drought (2001-2009).

The results of this analysis will be used in the future to compare drought severity with actual rates of wind erosion.