Abstract
Abstract. Eastern Australia has considerable mineral and energy resources, with areas of high biodiversity value co-occurring over a broad range of agro-climatic environments. Lack of water is the primary abiotic stressor for (agro)ecosystems in many parts of eastern Australia. In the context of mined land rehabilitation quantifying the severity–duration–frequency (SDF) of droughts is crucial for successful ecosystem rehabilitation to overcome challenges of early vegetation establishment and long-term ecosystem resilience. The objective of this study was to quantify the SDF of short-term and long-term drought events of 11 selected locations across a broad range of agro-climatic environments in eastern Australia by using three drought indices at different timescales: the Standardized Precipitation Index (SPI), the Reconnaissance Drought Index (RDI), and the Standardized Precipitation-Evapotranspiration Index (SPEI). Based on the indices we derived bivariate distribution functions of drought severity and duration, and estimated the recurrence intervals of drought events at different timescales. The correlation between the simple SPI and the more complex SPEI or RDI was stronger for the tropical and temperate locations than for the arid locations, indicating that SPEI or RDI can be replaced by SPI if evaporation plays a minor role for plant available water (tropics). Both short-term and long-term droughts were most severe and prolonged, and recurred most frequently in arid regions, but were relatively rare in tropical and temperate regions. Our approach is similar to intensity–duration–frequency (IDF) analyses of rainfall, which are crucial for the design of hydraulic infrastructure. In this regard, we propose to apply SDF analyses of droughts to design ecosystem components in post-mining landscapes. Together with design rainfalls, design droughts should be used to assess rehabilitation strategies and ecological management using drought recurrence intervals, thereby minimising the risk of failure of initial ecosystem establishment due to ignorance of fundamental abiotic and site-specific environmental barriers, such as flood and drought events.
Highlights
Eastern Australia holds vast mineral and energy resources of economic importance and internationally significant biodiversity (Williams et al, 2002; Myers et al, 2000) occurs over a broad range of agro-climatic environments (Hutchinson et al, 2005; Woodhams et al, 2012)
The same distributions fitted best to the drought severity and duration of the generated drought events based on the Frank rather than the Gumbel copula (R2 > 0.90, p < 0.05) (Appendix F)
In contrast to Wagga Wagga, the two tropical locations were characterised by distinct seasonality patterns and very low variation as indicated by the low ratio of winter to summer rainfalls (Table 1) and low coefficients of variation in severity and duration (Table 2)
Summary
Eastern Australia holds vast mineral and energy resources of economic importance and internationally significant biodiversity (Williams et al, 2002; Myers et al, 2000) occurs over a broad range of agro-climatic environments (Hutchinson et al, 2005; Woodhams et al, 2012). There are extensive areas of cropping and grazing such as in the Brigalow Belt Bioregion (Arnold et al, 2013) and the wheatbelt regions around Kingaroy and Wagga Wagga (Woodhams et al, 2012) (Table 1, Fig. 1). Lack of water availability is a critical factor for the mining industry, agriculture and biodiversity. Water deficit reduces agricultural productivity and increases the risk of failure of ecosystem rehabilitation. For some of the agro-climatic regions in eastern Australia, the lack of water is the primary abiotic stressor for (agro)ecosystems throughout the year, whereas for others water availability is at least seasonally limited (Table 1). Regions across Australia have regularly experienced periods of water deficit (Murphy and Timbal, 2008). Drought events are distributed diversely with regard to their duration, severity, and frequency of occurrence over the continent
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