Drought In South-eastern Australia Research Articles

Recession constants are non-stationary: Impacts of multi-annual drought on catchment recession behaviour and storage dynamics

Recession analysis is commonly adopted to characterise catchment behaviour, particularly in relation to the role of catchment storage in streamflow production. Recession techniques are data hungry and characterise average behaviour over long periods of recorded data, making them generally unsuitable in transient conditions. Nevertheless, in the context of multi-annual drought, sufficient data may be available to characterise temporal change by examining different subperiods. In this work, we assessed changes in recession behaviour of catchments affected by multi-annual drought in south-eastern Australia, focusing on how changes in recession patterns over time correlate to drought-induced shifts in annual rainfall-runoff relationships. We applied two methods, drawn from the vast methodological literature on recession analysis. They consider different information and entail different assumptions; one is based on average daily recession rates and the other on hourly recession slope plots. Despite the differences, their results are consistent: catchments that exhibited significant changes in rainfall-runoff relationship during the drought also display significantly steeper recessions during and after the drought. Subsequent investigation suggests that only a portion of the increases in recession speed are attributable to increased evaporative demand. Rather, they are likely caused by decreased connectivity between subsurface storage and catchment surface water and increased transmission losses through the streambed. With this work, we demonstrate the usefulness of recession analysis to investigate sources and effects of non-stationary behaviour, providing insights into the impacts of long-term drought on streamflow production and catchment storage dynamics.

Captive breeding of two rare non-migratory galaxiids (Teleostei: Galaxiidae) for species conservation

Devising effective techniques for breeding and rearing rare non-migratory galaxiids is urgently required for conservation purposes where few animals exist in the wild for translocation or reintroduction. The development of such protocols is particularly pertinent in light of recent intense widespread bushfires and long-term drought in southeastern Australia, which have increased the likelihood of the need for captive maintenance to protect and recover remnant species. In this study, we promoted reproductive maturation via manipulation of day length and temperature, and produced viable offspring from two small, endemic freshwater galaxiids, Galaxias fuscus (Mack 1936) and Galaxias longifundus (Raadik 2014) using in vitro propagation techniques. Propagation trials resulted in 425 oocytes being stripped from four ripe G. fuscus females, and 1527 oocytes from three ripe G. longifundus females. Of these, 342 (80.5%) G. fuscus and 968 (63.4%) G. longifundus eggs hatched into larvae. Newly hatched G. fuscus and G. longifundus larvae were transparent, and 8.4–9.7 mm (mean 9.0 mm TL) and 7.1–8.9 mm (mean 8.3 mm TL) consecutively. Absorption of the yolk sac by G. fuscus larvae (1.5–2.0 mm diameter) was complete 6–7 days after hatching, and for G. longifundus (1.0–1.4 mm diameter) 12–13 days after hatching. One-month-old G. fuscus measured ~16 mm and two-month-old larvae ~22 mm, and one-month-old G. longifundus ~11 mm. Methods and techniques employed may aid broader galaxiid conservation efforts.

Machine learning-based integration of remotely-sensed drought factors can improve the estimation of agricultural drought in South-Eastern Australia

Agricultural drought is a natural hazard arising from insufficient crop water supply. Many drought indices have been developed to characterize agricultural drought, relying on either ground-based climate data or various remotely-sensed drought proxies. Ground-based drought indices are more accurate but limited in coverage, while remote sensing drought indices cover large areas but have poor precision. Application of advanced data fusion approaches based on remotely-sensed data to estimate ground-based drought indices may help fill this gap. The overall objective of this study was to determine whether various remotely-sensed drought factors could be effectively used for monitoring agricultural drought in south-eastern Australia. In this study, thirty remotely-sensed drought factors from the Tropical Rainfall Measuring Mission (TRMM) and the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite sensors were used to reproduce a ground-based drought index, SPEI (Standardized Precipitation Evapotranspiration Index) during 2001–2017 for the New South Wales wheat belt in south-eastern Australia. Three advanced machine learning methods, i.e. bias-corrected random forest, support vector machine, and multi-layer perceptron neural network, were adopted as the regression models in this procedure. A station-based historical climate dataset and observed wheat yields were used as reference data to evaluate the performance of the model-predicted SPEI in reflecting agricultural drought. Results show that the bias-corrected random forest model outperformed the other two models for SPEI prediction, as quantified by the lowest root mean square error (RMSE) and the highest R2 values (<0.28 and ~0.9, respectively). Drought distribution maps produced by the bias-corrected random forest model were then compared with the station-based drought maps, showing strong visual and statistical agreement. Furthermore, the model-predicted SPEI values were more highly correlated with observed wheat yields than the station-based SPEI. The method used in this study is effective and fast, and based on data that are readily available. It can be easily extended to other cropping areas to produce a rapid overview of drought conditions and to enhance the present capabilities of real-time drought monitoring.

Anuran responses to pressures from high-amplitude drought–flood–drought sequences under climate change

We measured changes in the occurrence, abundances and evidence of breeding of frogs to a sequence of severe drought–extreme wet–drought in south-eastern Australia, which is projected to characterize the regional climate in the coming decades. We collected data on anuran abundances, species richness and breeding by using aural surveys and visual searches in 80 waterbodies in 10 landscapes. We surveyed six times during the austral winter-springs of 2006 and 2007 (9–10 years into the 13-year ‘Big Dry’ drought), six times in the corresponding seasons of 2011 and 2012 (the ‘Big Wet’) and another six times in 2014 and 2015, which had lapsed into another intense dry period (‘post-Big Wet’). The relatively small gains in species occupancy rates and evidence of breeding achieved during the Big Wet following the Big Dry were eroded and reversed in the years after the Big Wet period, with several biotic measures falling substantially below the values for the Big Dry. The global prognosis is for long-term drying and warming, notwithstanding much geographic variation in the degree and temporal patterns of drying. Longer droughts with short periods of wet/benign conditions are projected for many parts of the world. For water-dependent fauna such as most amphibians, our results signal widespread declines in lowland regions experiencing such patterns. If droughts exceed lifespans of frogs, then resistance to drought will be so low that populations will plunge to levels from which the short periods of more benign conditions will be insufficient to enable substantial recovery.

Re-evaluating sowing time of spring canola (Brassica napus L.) in south-eastern Australia—how early is too early?

Optimising the sowing date of canola (Brassica napus L.) in specific environments is an important determinant of yield worldwide. In eastern Australia, late April to early May has traditionally been considered the optimum sowing window for spring canola, with significant reduction in yield and oil in later sown crops. Recent and projected changes in climate, new vigorous hybrids, and improved fallow management and seeding equipment have stimulated a re-evaluation of early-April sowing to capture physiological advantages of greater biomass production and earlier flowering under contemporary conditions. Early–mid-April sowing generated the highest or equal highest yield and oil content in eight of nine field experiments conducted from 2002 to 2012 in south-eastern Australia. Declines in seed yield (–6.0% to –6.5%), oil content (–0.5% to –1.5%) and water-use efficiency (–3.8% to –5.5%) per week delay in sowing after early April reflected levels reported in previous studies with sowings from late April. Interactions with cultivar phenology were evident at some sites depending on seasonal conditions. There was no consistent difference in performance between hybrid and non-hybrid cultivars at the earliest sowing dates. Despite low temperatures thought to damage early pods at some sites (&lt;−2°C), frost damage did not significantly compromise the yield of the early-sown crops, presumably because of greater impact of heat and water-stress in the later sown crops. A validated APSIM-Canola simulation study using 50 years of weather data at selected sites predicted highest potential yields from early-April sowing. However, the application of a frost-heat sensitivity index to account for impacts of temperature stress during the reproductive phase predicted lower yields and higher yield variability from early-April sowing. The frost–heat-limited yields predicted optimum sowing times of mid-April at southern sites, and late April to early May at the northern sites with lower median yield and higher yield variability in crops sown in early April. The experimental and simulation data are potentially compatible given that the experiments occurred during the decade of the Millennium drought in south-eastern Australia (2002–10), with dry and hot spring conditions favouring earlier sowing. However, the study reveals the need for more accurate and validated prediction of the frost and heat impacts on field-grown canola if simulation models are to provide more accurate prediction of attainable yield as new combinations of cultivar and sowing dates are explored.

Did spatial and temporal variations in water quality influence cyanobacterial abundance, community composition and cell size in the Murray River, Australia during a drought-affected low-flow summer?

Severe drought in south-eastern Australia during the 2008–2009 spring, summer and autumn period resulted in low flows in the Murray and Edward Rivers, a major river system of the region. We investigated whether such conditions produced marked spatial and temporal variations in water quality and in the abundance, community composition and cell size of six commonly occurring cyanobacterial species in the river. Water quality data and cyanobacterial samples were collected at 22 sites spanning almost 1900 km of river. Significant spatial and temporal variation in water quality was found in the rivers. Four cyanobacterial species had significantly higher abundances in the upper and middle sections of the Murray and Edward Rivers, and significant temporal variations occurred in three species. Community composition also varied significantly both spatially and temporally. There were significant spatial differences in the cell size of three species, and significant temporal variation occurred in five species. However, water quality was found to provide a poor explanation of the variance observed in the cyanobacteria, possibly due to their continual replacement by river flow at the sampling sites. Increased cyanobacterial occurrence in rivers is likely to be more common under future climate change scenarios.

Floodplain vegetation of the River Murray in 1987–1988: an important pre-drought benchmark for subsequent studies.

Floodplain vegetation of the River Murray in 1987–1988: an important pre-drought benchmark for subsequent studies.

Sustainable irrigation: How did irrigated agriculture in Australia's Murray–Darling Basin adapt in the Millennium Drought?

The recent drought in south-eastern Australia saw the lowest inflows on record in the Murray–Darling Basin in 2006. As reservoirs were drawn down water availability for irrigation was cut. In 2007–2008 and 2008–2009, irrigators received about one third of their pre-drought allocations. Understanding how the irrigation sector adapted to less water will help planning for the next drought and a future in which irrigation water use will be reduced permanently in the basin.The aggregate responses that we report are consistent with reported data on strategies used by irrigators to adapt to less water, including water trading, input substitution, changes to crop mix, and improvements to technology leading to reduced water application rates and yield increases. These responses likely also provide some insight on how irrigators will adapt to future more permanent reductions in irrigation water and assist in the identification of constraints to adaption.

A review of on-ground recovery actions for threatened freshwater fish in Australia

Freshwater fish are a highly threatened group and recovery of these threatened species is an increasingly difficult ecological and social challenge. There are many different on-ground recovery actions available to managers, but no synthesis of what, how or why these recovery actions have been deployed. The present paper reviews 428 reported on-ground recovery actions from a survey of practitioners of threatened freshwater-fish recovery in Australia. Recovery actions were grouped into 12 categories, with the most commonly utilised recovery categories being harvest control, translocation, habitat enhancement and stock enhancement. Major drivers of recovery actions were general conservation concern, recovery plans and emergency responses. The number of recovery actions grew significantly in the decade beginning 2000 as the impacts of prolonged drought in south-eastern Australia intensified. In all, 58% of recovery actions occurred in the Murray–Darling Basin, although this region holds only 27% of the 74 listed threatened freshwater fish in Australia. Few or no recovery actions were reported for many species, and few actions occurred in northern or western parts of the country. More than 80% of recovery actions reportedly had some form of monitoring. The diversity of management interventions is reviewed, and patterns and issues are identified to guide future recovery efforts.

Drought, floods and water quality: Drivers of a severe hypoxic blackwater event in a major river system (the southern Murray–Darling Basin, Australia)

Summary Hypoxic blackwater events are characterised by high levels of dissolved organic carbon in the water column, the metabolism of which depletes dissolved oxygen, which can cause fish and crustacean mortality. Understanding the drivers of and controls on hypoxic blackwater events is important in order to reduce the potential for detrimental water quality impacts from both managed and natural flows. After a decade-long drought in south-eastern Australia, a series of spring and summer flood events in 2010–2011 resulted in a large-scale hypoxic blackwater event in the southern Murray–Darling Basin that affected over 2000 km of river channels and persisted for 6 months. We examined the biogeochemistry and hydrology underpinning this extreme event and found that multiple drivers contributed to the development and persistence of hypoxic blackwater. Inundation of both forested and agricultural floodplains that had not been flooded for over a decade mobilised large stores of reactive carbon. Altered flow seasonality, due to a combination of climatic effects and river regulation, not only increased the risk of hypoxic blackwater generation but also shifted the proportion of bioavailable carbon that was returned to the river channels. Hypolimnetic weir discharge also contributed to hypoxia at some sites. These findings highlight the need for a whole-of-system perspective for the management of regulated river systems – especially in the face of a changing climate.

Farming suicides during the Victorian drought: 2001–2007

The objective of this study was to determine whether farming suicides increased in Victoria during the prolonged drought in south eastern Australia and gain an understanding of Victorian farming suicides during the period. Intentional self-harm deaths of farmers and primary producers notified to the Victorian State Coroner from 2001 to 2007 were examined to identify characteristics and determine whether the annual number of farming suicides increased. Farming suicides accounted for just over 3% of Victorian suicides. The total number of farming suicides was 110 for the period and ranged between 11 and 19 deaths per year, rising and falling inconsistently from year to year. Males accounted for nearly 95% of farming suicides, with firearms and hanging the most frequently used methods, and most deaths occurring between 30 and 59 years of age. The small number of relevant cases and fluctuations in the annual number of deaths provides no evidence of a pattern of increasing farming suicides during the drought years, when there was approximately one suicide every 3 weeks. Given the elevated suicide risk in male farmers and association with multiple psychosocial and environmental factors, it cannot be concluded, however, that suicide risk itself did not increase during this period of heightened uncertainty and stress. Drought should not be dismissed among the many risk factors, and it is possible that increased mental health awareness and community support programs targeting drought-affected areas contributed to improved management of stress and suicide risk in regional and rural Victoria over the past decade.

The potential to reconstruct broadscale climate indices associated with southeast Australian droughts from Athrotaxis species, Tasmania

Occurrence of drought and dry periods in southeastern Australia has been linked to broad scale climate phenomena including the Southern Oscillation, Interdecadal Pacific Oscillation (IPO), Indian Ocean Dipole (IOD), Southern Annular Mode (SAM) and persistence of blocking high pressure in the Tasman Sea. We examine relationships between Athrotaxis tree ring chronologies from southern Australia extending over much of the past millennia and these broad scale indices. We also examine relationships between the chronologies, temperature, precipitation and a standardised precipitation and evapotranspiration index. Timing of significant correlations with maximum temperature varies between species. The responses of the species with broadscale indices vary with location: northern Athrotaxis cupressoides (Pencil Pine) are more strongly related to the Interdecadal Pacific Oscillation (IPO) and Southern Oscillation Index (SOI) than southern sites. As an exception to this, a site in the far south had significant correlations with both the SOI and IPO, opposite in sign to those observed for the northern sites. Significant spectral power at frequencies consistent with the SOI and IPO occur in all chronologies. Western and southern sites are more strongly related to a seasonalised index of SAM. These three systems have played important roles in determining moisture conditions in southeastern Australia over the past millennium. Results suggest that reconstructions of the SOI, IPO or SAM are unlikely based solely on this Athrotaxis network. The Athrotaxis network of tree ring sites, is however, likely to be an important input to multi-proxy models reconstructing the SOI, IPO or SAM in the Australian sector. The Athrotaxis network of sites is also an important extension of the existing network of Australian tree ring sites that could be used to reconstruct historical drought in southeastern Australia.

A Note on Tree Deaths during the Current (2001–?) Drought in South-eastern Australia

Tree deaths over large areas during droughts are uncommon. In the semi-arid zone of New South Wales (NSW) such events were last reported during the prolonged droughts of 1895–1903 and 1939–45, though whether caused solely by drought is open to question. Anecdotal and quantitative evidence during the current prolonged drought (2001–?) in NSW's sub-humid zone (where deaths are localised) and semi-arid zone (where deaths are more extensive) suggest that climatic conditions are comparable to, and perhaps more severe than, those of the earlier prolonged droughts. It is suggested that lack of access to deep soil moisture due to inherent shallow rooting, or due to site conditions, is the most likely cause; and that this may be associated with higher than optimal tree densities in cohorts of trees that arose from previous regeneration events during periods of well above average rainfall. A more thorough examination of the extent and severity of this event is warranted.

The association between congenital chondrodystrophy of unknown origin (CCUO) in beef cattle and drought in south-eastern Australia

Reports of congenital chondrodystrophy of unknown origin (CCUO) have been anecdotally associated with periods of drought during the gestation period of affected beef calves. Reported sporadically in the past, the incidence of CCUO has increased in south-eastern Australia and has been reported every year between 2002 and 2007. A maternal nutritional deficiency arising from poor quality pastures and supplements has been suggested as contributing to the disorder. With an increase in drought occurrence predicted by climate change models, it is possible that the incidence will increase into the future. Retrospective data collected during a case control study was used to determine if the occurrence of cases of CCUO was associated with rainfall deficiency during gestation. A total of 799 cases occurring on 46 farms in south-eastern Australia were identified and a time series of cases was created. The association of both average monthly and three-month average rainfall with cases of CCUO revealed a significant negative correlation ( r = −0.29 and r = −0.37 respectively, P < 0.05) five months prior to the birth of CCUO calves on the farms studied. Logistic regression analysis showed a 3.3 (CI 1.8; 5.8, P < 0.001) times increased risk of CCUO calves when the three-month average rainfall was in the lowest decile five months prior to the birth of calves. This information may be used to alert farmers as to when high quality supplemental feed may be provided to improve maternal nutrition and reduce the number of CCUO calves born.

Climate-driven mobilisation of acid and metals from acid sulfate soils

The recent drought in south-eastern Australia has exposed to air, large areas of acid sulfate soils within the River Murray system. Oxidation of these soils has the potential to release acidity, nutrients and metals. The present study investigated the mobilisation of these substances following the rewetting of dried soils with River Murray water. Trace metal concentrations were at background levels in most soils. During 24-h mobilisation tests, the water pH was effectively buffered to the pH of the soil. The release of nutrients was low. Metal release was rapid and the dissolved concentrations of many metals exceeded the Australian water quality guidelines (WQGs) in most tests. The concentrations of dissolved Al, Cu and Zn were often greater than 100× the WQGs and strong relationships existed between dissolved metal release and soil pH. Attenuation of dissolved metal concentrations through co-precipitation and adsorption to Al and Fe precipitates was an important process during mixing of acidic, metal-rich waters with River Murray water. The study demonstrated that the rewetting of dried acid sulfate soils may release significant quantities of metals and a high level of land and water management is required to counter the effects of such climate change events.

The autumn break for cropping in southeast Australia: trends, synoptic influences and impacts on wheat yield

AbstractThe autumn break is the first significant rainfall event of the winter growing season. Two definitions of the autumn break have been developed for northwestern Victoria; a so‐called ideal break and a minimum rainfall condition for sowing a wheat crop termed a minimal break. Application of the ideal break definition for an eight‐station average reveals that 41 autumn breaks occurred in the first half of the record (1889–1947) and 34 in the second half (1948–2006) with a trend towards breaks occurring later in the season. In the decade to 2006, there have been only 3 ideal breaks (1999, 2000 and 2005) and none of the selected rainfall stations has recorded an ‘extreme’ wet autumn over the last 11 years, the longest period recorded for this criterion. A synoptic analysis for the period 1956–2006 has established that breaks are predominantly associated with systems known as cutoff lows. The influence of these systems has varied markedly throughout the analysis period and only one autumn break has been caused by a cutoff low in the final decade of the analysis. Additionally, the total rainfall associated with cutoff lows in the April to June period has declined significantly over the past 30 years.A farming system model has been employed to simulate a wheat crop in northwestern Victoria under historical conditions for a range of management options. Average yield across all years of the simulation declines with delay in the sowing date after late April, but there is a marked interannual variability in yield response to the sowing date which is related to rainfall distribution in the growing season in each year. The simulated in‐crop rainfall indicates that the most recent drought in southeastern Australia is comparable in severity with the two major droughts in the 20th Century. Copyright © 2008 Royal Meteorological Society

The transpiration response by four topographically distributed Eucalyptus species, to rainfall occurring during drought in south eastern Australia

Vegetation covers a substantial proportion of the terrestrial Earth surface and where removed from human influence has evolved influenced mainly by climatic and edaphic constraints. Over the past 200 years, substantial tracts of the wheat‐sheep belt of southern Australia has been cleared of native vegetation and replaced by annual crop and pasture species. As a consequence, there has been a change in the water balance of many catchments as now more water leaks beneath the roots of introduced plants, contributing to groundwater rise and expansion in the amount of land affected by salinization. In an attempt to arrest root zone leakage, scientists and managers acknowledge the need for new agricultural practices which mimic the ecohydrological behaviour patterns of remnant vegetation.In this paper, we examine the water use characteristics of four woodland Eucalyptus species growing in different topographic and edaphic environments in south eastern Australia. Eucalyptus sideroxylon and E. rossii were the sub‐ and dominant species inhabiting the stony ridges, while in the adjacent valleys E. macrorhyncha and E. albens were the sub‐ and dominant species, respectively. At the two locations, sub‐dominant species were highly responsive to episodic rainfall events both during and following drought, and exhibited distinct seasonality in daily transpiration rate; while the dominant species at each location was less responsive to rainfall and water use appeared to be less seasonally dependent. Analysis of the water use response indicated that the two sub‐dominant species had shallower roots while the major of roots of the dominant trees were likely to be located deeper in the substratum. This suggested that the stony ridges may store water deeper in the substratum than previously thought, to sustain some remnant vegetation over the dry summers, and ultimately, contribute less recharge to groundwater.

Growth of Subalpine Shrubs and Snowgrass Following a Rare Occurrence of Frost and Drought in Southeastern Australia

From March 1982 to March 1983, the subalpine tract of the Bogong High Plains in southeastern Australia was subject to a series of unusual climatic events. Relatively severe frosts occurred during autumn and winter, snow cover during winter was low, and the 1982/83 summer was particularly dry. This combination of frost and drought is the only one recorded over the past 50 yr. The net annual aboveground production of the dominant shrubs from open grassy-heath and closed heath communities ranged from 480 to 830 g m-2 yr-', with greater production by shrubs within more sheltered, closed heath communities. These values were considerably greater than those of snowgrass (Poa sp.) within grassy swards in these two community types, (135 g m-2 yr-'). Such a combination of climatic events may have longlasting effects, and in particular may favor the growth of the shrubs over snowgrass where these two different life forms are competing within the shrub-grass complex.