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In the North West Shelf region of Australia is a surface current (Holloway Current), which flows southwestward along the shelf break. This paper describes a seasonal undercurrent below the Holloway Current. A 5-day climatology is constructed from the output of an eddy-resolving oceanic general circulation model (OGCM). A seasonal northeastward-flowing undercurrent is found on the upper continental slope during the climatological April-May. This undercurrent reverses during February-March. During its annual cycle, the phase of the undercurrent tends to propagate southwestward and upward. The annual frequency dominates, but the positive and negative phases of the undercurrent are not symmetric in the yearly cycle because of the contributions from the semi-annual and 1/3-annual components. We propose a hypothesis that this undercurrent is a beam of coastal trapped wave (CTW). As an initial attempt to assess the plausibility of this hypothesis, we construct an idealized linear coastal-trapped wave (CTW) solution driven by an idealized harmonic meridional winds at the annual frequency. The solution takes the form of a beam originating from the forcing region on the continental shelf and propagating offshore and southward. When it emerges on to the continental slope, it takes the form of an undercurrent. This idealized solution shares several properties with the undercurrent in the OGCM despite several discrepancies. [ABSTRACT FROM AUTHOR]

Antarctica is a crucial regulator of the world's climate, and as environmental security permeates global security, using Antarctic science to better understand climate is becoming increasingly pressing. Although the Australian Government has recognised that climate change poses 'a current and existential national security' threat and has acknowledged Antarctica's importance regarding the earth's global climate system, the focus of Australia's intelligence community pertaining to Antarctica currently remains restricted to upholding the military-security and diplomatic goals of the Antarctic Treaty System (ATS). This current focus aims to hedge against the possibility of conflict on, or over, the frozen continent via 'working the ATS', however, this paper argues that Antarctic climate science holds a greater capacity to deliver security outcomes for Australia. Antarctic climate science offers opportunities regarding intelligence for Antarctica, that is, securing Australia's Antarctic interests, as well as regarding intelligence from Antarctica; by enhancing natural disaster preparedness, bolstering broader strategic planning, as well as furthering diplomacy and the legitimisation of Australia's leadership on, and over, the frozen continent. It is recommended that the Commonwealth Government establish a climate intelligence working group to ensure the utility of climate science to security and intelligence is realised. [ABSTRACT FROM AUTHOR]

Australian media reporting of climate change and renewable energy, along with public perceptions of the science and solutions of climate change, have shifted in ways that have increased pressure on politicians and policy makers. With the promotion of renewable energy central to ending Australia's heavy reliance on fossil fuels, it is critical to understand how this complex intersection of media and politics is evolving with regard to Australia's renewable energy options. Therefore, this paper examines Australian newspaper reporting of a pivotal moment in Australia's renewable energy discourse: the Australian Government's announcement, in March 2017 to expand the seventy-year-old Snowy Mountains Hydroelectric Scheme (known as Snowy 2.0), which marked a turning point in conservative energy policy. Qualitative content analysis reveals that, while political discourse delimited newspaper narratives, the sentiment of the framing was most strongly associated with the partisan alignment of the publishing organization. Regional influences also had a minor association with the framing of renewable energy. Through close analysis of this decisive moment in Australian media's political representation of renewable energy, this paper offers insights that can be used to inform media strategies for renewable energy policy in Australia, and to track changes in framing over time. [ABSTRACT FROM AUTHOR]

Climate change introduces greater complexity to water resources planning, requiring techniques suited to increased future uncertainties. In Australia's Murray Darling Basin, governments formally recognised climate risk in 2002 and legislated science-based climate risk assessment in 2007. Since then, research has helped clarify the significance of climate change impacts on catchments, riverine ecosystems and water resources. This paper offers a review of climate risk assessments undertaken over the past two decades and outlines research needs and policy options while noting there are no simple solutions given the systemic nature of climate risks. Water resource planning and climate risk assessment need to handle non-stationarity and post-natural Anthropocene conditions. These methods should integrate biophysical and socio-economic modelling, increase stakeholder participation in developing and testing policy options and codify standards and procedures for transparency. [ABSTRACT FROM AUTHOR]

Compound extreme natural events cause a significantly larger impact than individual extreme events. Therefore, the urgency of exploring the climatology of compound events is growing. This paper is aimed to identify the current hotspots of compound heatwaves and droughts (CHD) and trends in their occurrence in southeast Australia. In this context, 61 weather stations were selected from the study area, and analyses were carried out over the extended summer season of the time period 1971–2021. The hotspots of CHDs in southeast Australia were identified considering both the total count of CHD days and 90th percentile of CHDs during the study period. The study period was divided into two periods 1971–2000 and 2001–2021, to assess the change in hotspots spatially and temporally. Four different attributes of CHDs based on the number, duration, severity and amplitude of CHDs were also calculated, and Mann–Kendall (MK) test followed by Sen's slope was adopted to detect the trends in all these four attributes of CHDs. Trends in CHD indices were also calculated for the two periods of 1971–2000 and 2001–2021. For calculating the CHD, excess heat factor (EHF) was used to identify the heatwaves. In the case of drought identification, SPEI and SPI drought indices were adopted with aggregation of 3 and 126 antecedent months, and three different threshold values were selected to consider three levels of dry conditions, e.g. 0, − 0.5 and − 1.0. It has been found that more CHDs occurred on the eastern side of NSW and Queensland states. Furthermore, the total count of CHD days increased notably during the last two decades. The trends in CHD indices were found to be significant in the recent period (2001–2021), and there was no trend in the earlier period (1971–2000). The findings of this study will help to plan heat and drought-related emergency management in the study area. [ABSTRACT FROM AUTHOR]

Exposure to weather extremes, such as heatwaves, can cause discomfort, harm, or death in grazing cattle in pastures. While the Australian Bureau of Meteorology issues sheep graziers alerts when there is an exposure risk to chill for livestock, there is no equivalent alert for heat stress for Australian cattle. Before any such alert system can be developed, a robust assessment and comparison of relevant cattle thermal stress indices is required. This study evaluates and compares the multiyear climatology of three cattle thermal heat stress indices across Australia in the warm season months (October–March). The same indices are then used to assess historical Australian heat events where cattle died from heat exposure. These events are based off official records and survey responses from northern Australian graziers. In the seven historical heat events studied, high relative humidity combined with low wind speeds, or high solar exposure combined with high surface temperatures, exacerbated the impact of heat stress on cattle. In the two historic events where multiple compounding weather factors combined (e.g., high humidity, low winds, and high solar exposure), the cattle mortality levels were significantly high. These events were characterized by rainy conditions followed by a rapid warming, meaning cattle were likely unable to acclimatize to such dramatic temperature changes. This study highlights the need for using more than one thermal stress index when verifying cattle heat stress events and, importantly, calls for further research on standardizing the risk classifications of these thermal indices for cattle in Australia's variable climate. Significance Statement: Cattle across Australia's northern tropical and semiarid regions often experience extreme hot and humid conditions in the summer months, which increases the risk of heat stress. This is the first study of its kind to evaluate observations of cattle heat stress across Australia using indices that describe the combined effects of solar exposure, wind speed, relative humidity, and surface temperatures. These cattle heat stress indices can be used to evaluate historical cattle mortality events in feedlots and in grazed pastures. This study lays the groundwork for the development of Australian-wide cattle heat stress forecast products on the 7-day to multiweek time scales. [ABSTRACT FROM AUTHOR]

Background: Historical records of fire weather phenomena provide valuable insights into spatial and temporal trends which can inform further research and are important tools for planning. Aims: We outline a 19-year climatology of a Research Prototype (AFDRSRP), of the new Australian Fire Danger Rating System, documenting its spatial and temporal characteristics. Methods: The analysis utilises the Australian Bureau of Meteorology's high-resolution reanalysis suite (BARRA), together with fuel data provided by Australian fire agencies. We examine the spatial and temporal distribution of the AFDRSRP. Distributions are categorised by fuel type, analysing relative variability across time and space. Key results: The results validate the broad behaviour of the new system and provide insight into the variation of fire danger throughout Australia, adding detail to the understanding of timing of peak fire danger both diurnally and annually. Conclusions: While the AFDRSRP differs from the operational system in its fire danger rating categories and tuning of algorithms, it nonetheless provides useful insights into the operational implementation. Implications: These results will be essential for planning during fire seasons. We present a 19-year climatology of the Australian Fire Danger Rating System: Research Prototype (AFDRSRP), recently implemented operationally throughout Australia. The climatology describes the typical spatial and temporal behaviour of the AFDRSRP. It is important for users to improve familiarity with the new system, and to ensure it performs as expected. This article belongs to the Collection Australian Fire Danger Rating System. [ABSTRACT FROM AUTHOR]

The inter-dataset agreement of trends in subweekly near-surface (850 hPa) temperature variability over Southern Hemisphere midlatitude land masses is assessed among 12 global atmospheric reanalysis datasets. A comparison of the climatological temperature variance and dominant sources and sinks of the variance reveals that, except for NCEP-NCAR (R1) and NCEP-DOE (R2), there is a relatively good agreement for their magnitudes and spatial distributions during the satellite era (1980–2022), which indicates that the key features of subweekly variability are sufficiently well represented. A good agreement is noted for the positive trends found in subweekly variability over the satellite era affecting South Africa in September–October–November (SON) and South America in December–January–February (DJF). Although there is agreement in most of the reanalyses concerning the positive trend affecting Australia in SON, this has not yet emerged from the noise associated with interannual variability when considering only the satellite era. It is significant, however, when the period is extended (1954–2022) or limited to the most recent decades (1990–2022). The trends are explained primarily by a more efficient generation of subweekly temperature variance by horizontal temperature advection. This generation is also identified as a source of biases among the datasets. The trends are found to be reproduced even in those reanalyses that do not assimilate satellite data (JRA-55C) or that assimilate surface observations only (ERA-20C, 20CRv2c, and 20CRv3). [ABSTRACT FROM AUTHOR]

Spatial information of climatological frequency distribution of daily precipitation is highly valuable for a wide range of applications. Accurate estimation of climatology can be made for gauged locations where quality and lengthy observations are available. For ungauged or poorly gauged locations, however, indirect estimation is needed. One approach is to use a gridded daily precipitation dataset derived from interpolating observations. However, gridded daily precipitation data can be subject to large errors when gauge density is low. In addition, most interpolation methods tend to smooth the extreme values and increase the low ones, leading to unrealistic statistical properties and therefore poor estimation of daily climatology. Another approach is to first derive climatology at gauged locations and then interpolate climatology to ungauged locations. While this approach is likely to be more robust than the first approach, low gauge density can still cause significant errors especially in areas of complex terrain. In this study, we develop a method that postprocesses spatially consistent and rich reanalysis data using accurate observations at gauged locations. At an ungauged location, daily precipitation amounts from the reanalysis are bias‐corrected using quantile‐mapping guided by frequency distributions of reanalysis data and observations at a nearby gauged location (reference location). The bias‐corrected precipitation amounts are then used to estimate the climatology for the ungauged location. This method eliminates the need for interpolation and therefore its adverse effects. Special care is taken in quantile‐mapping when extrapolating beyond the range of reanalysis data at the reference location. We evaluate the method at 50 locations in Australia, using the Bureau of Meteorology Atmospheric high‐resolution Regional Reanalysis for Australia (BARRA) and precipitation observation network across Australia. These locations are chosen to represent different climate regions in Australia and have observations to validate the postprocessed reanalysis climatology of daily precipitation. Results show that the postprocessed climatology is consistent with observations, in terms of frequency distribution, high quantiles, probabilities of wet and dry days and their transitions. [ABSTRACT FROM AUTHOR]

This study describes flash drought (FD) inferred from the evaporative stress index (ESI) over Australia and its relationship to vegetation. During 1975–2020, FD occurrence ranges from less than 1 per decade in the central arid regions to 10 per decade toward the coasts. Although FD can occur in any season, its occurrence is more frequent in summer in the north, winter in the southern interior and southwest, and across a range of months in the far southeast and Tasmania. With a view toward real-time monitoring, FD "declaration" is defined as the date when the ESI declines to at least −1, i.e., drought conditions, after at least 2 weeks of rapid decline. Composite analysis shows that evaporative demand begins to increase about 5–6 weeks before declaration with an increase in solar radiation, while evapotranspiration initially increases with evaporative demand but then decreases in response to the soil moisture depletion. Solar radiation increases simultaneously with precipitation deficit, both reaching their peak around declaration. FD intensity peaks with soil moisture depletion, 2–3 weeks after declaration. The composite wind speed only shows a modest increase around declaration. The composite FD ends 4 weeks after rapid decreases in solar radiation and increases in precipitation. Satellite-derived vegetation health composites show pronounced decline in the nonforested regions, peaking about 4–8 weeks after FD declaration, followed by a recovery period lasting about 12 weeks after flash drought ends. The forest-dominated regions, however, are little impacted. Modeled pasture growth data show reduced values for up to 3 months after the declaration month covering the main agricultural areas of Australia. Significance Statement: Flash drought describes a fast intensification or rapid development of drought conditions with potential severe impacts on agriculture and ecosystems. This study describes the climatology and typical evolution of flash drought over Australia for the period 1975–2020. An objective definition of flash drought, using high-resolution observational-based datasets, is proposed and its spatiotemporal variability is provided, as well as its relationship with vegetation health and pasture growth. This constitutes a guideline for understanding flash drought in Australia and its impacts on vegetation. [ABSTRACT FROM AUTHOR]

Terrestrial ecosystems are fully coupled with the climate. The planet has been greening owing to the increased vegetation growth in response to the changing atmosphere, which in turn has feedback on the climate. Greening has slowed down the rise in global land-surface air temperature mainly through a coincident increase of evapotranspiration and precipitation in wet regions. In dry regions, greening intensifies the decrease in soil moisture induced by greening-enhanced transpiration. Uncertain, however, is how the climate effects of greening in semi-arid lands might differ for variable wet and dry conditions. Here, we focus on the biosphere–atmosphere interactions in Australia by modeling the perturbation of vegetation changes under various states of sea surface temperature (SST), including the climatology mean, El Niño, and La Niña conditions. For the dry conditions of El Niño, greening exacerbates water stress and largely depletes the soil moisture, while for the wet conditions of La Niña, greening-enhanced evapotranspiration and precipitation resupply the soil moisture. For the normal conditions using the climatology mean SST, a small decrease in soil moisture occurs but with large spatial contrast because of heterogeneous changes of evapotranspiration and precipitation induced by greening. We emphasize that the alternating dry and wet conditions modulated by the large-scale climate variability are vital to understanding the response of climate to greening. Furthermore, vegetation-based warming mitigation policies need to be cautious when inferring distinct climate effects associated with greening. [ABSTRACT FROM AUTHOR]

The post-war era of the 1940s is known for the birth of global governance, a time when Western nations united in efforts to reconstruct the war-torn world and reflected on the role of science in society. History and philosophy of science (HPS) was one of the early projects that emerged out of the war years. Diana (Ding) Dyason who headed the first HPS department in the southern hemisphere is honoured by this annual lecture, the text of which constitutes this article. Thomas Kuhn's influential lecture in Oxford in 1961 inspired her work on the history of scientific entanglement with social concerns, and the directions of HPS at the University of Melbourne. Post-war reconstruction was both a local and a national project for every nation, very much in the air in the 1940s, and influential until the 1970s. The Australasian Association of Scientific Workers (AASW) brought together scientists too old to serve, or, in reserved occupations, to undertake their own 'war effort' on the question of: 'What comes next?' AASW held a planning conference in Sydney in 1944 to 'formulate a policy on the organisation of science necessary to meet the demands of post-war Australia'. They set out to consider the role of the 'the scientific method' in the welfare of society. In particular, they recognised their existing international scientific networks and connections could become valuable for post-war collaborations between different sciences and different nations of benefit to Australia and the world. The idea of 'the environment' was one of many that emerged internationally in these 'world-minded' times, an idea that focused on the management of nature for the benefit of people using the scientific method. National Parks were a crucial discussion point, bringing together amateur naturalists and professional environmental managers of all sorts in discussions about landscape planning along with international comparative work on reserving places for wild animals and plants. This Dyason Lecture explores the emergence of 'integrated science', of science in the service of society, that later included natural resource management, big science, environmental science, earth systems science and climate science. It begins with the tragedy of the 'dirty thirties', when soil was in the air, and the scientific response to concerns about feeding the world. Originally presented on 25 November 2021 at the University of Melbourne as a keynote of the Australasian Association for the History, Philosophy and Social Studies of Science. The lecture explores the history of interdisciplinary knowledge and integrated science, by pairing the post-war stories of history and philosophy of science (HPS) (the traditional focus of the Dyason Lecture) with a history of soil conservation as an integrating environmental science, in Australia and globally, from the war years until the Anthropocene. [ABSTRACT FROM AUTHOR]

This invited review outlines a selection of recent technical and communication advances, in certain areas of climate and weather science that could improve the capability and utility of drought early warning systems in Australia. First, a selection of current operational outputs and their significance for drought early warning is reviewed, then a selection of advancements in the Research and Development (R&D) pipeline are considered, which have potential to help enable better decision-making by stakeholders subject to drought risk. The next generation of drought early warning systems should have a focus on index- and impact-based prediction models that go beyond basic weather and climate parameters, at seasonal through to multi-year timescales. Convergence and integration of emerging research, science and technology is called for across the fields of climate, agronomy, environment, economics and social science, to improve early warning information. The enablement of more predictively based drought policy, should facilitate more proactive responses by stakeholders throughout the agricultural value chain, and should make stakeholders more drought resilient. [ABSTRACT FROM AUTHOR]

This brief study investigates the subtle ways that language can be used to subconsciously shape a reader's opinions about climate science within conservative news texts. To do so, our study employed techniques from critical discourse analysis to highlight the role of 'journalistic voice' and consider the granular linguistic techniques these outlets may use to subliminally validate sceptical viewpoints, while casting doubt on those espousing the consensus position. We found that certain semantic structures used in conservative climate reporting can take an otherwise apolitical analysis of climate issues, and potentially guide readers to a reactionary conclusion. Our analysis arrived at this position after undertaking a critical discourse analysis of the ways in which sceptical and non-sceptical climate 'experts' have been framed by Australia's largest conservative broadsheet newspaper, News Corp's The Australian, in the period after it changed its official position on climate to one of accepting the consensus view. [ABSTRACT FROM AUTHOR]

Multi-decadal ocean time-series are fundamental baselines for assessing the impacts of environmental change, however, compiling and quality controlling historic data from multiple sources remains challenging. Here we aggregate, document, and release a number of long time-series temperature products and climatologies compiled from data obtained at 4 monitoring sites around Australia where sub-surface ocean temperature has been recorded nominally weekly to monthly since the 1940s/50s. In recent years, the sampling was augmented with data obtained from moored sensors, vertical profiles and satellite-derived data. The temperature data have been quality controlled, and combined using a rigorously tested methodology. We have packaged the multi-decadal, multi-depth, multi-platform temperature time-series at each site and produced a range of daily temperature climatologies from different data combinations and time periods. The 17 data products are provided as CF-compliant NetCDF files and will be updated periodically. The long-term temperature time-series will be useful for studies of ocean temperature variability, trends, anomalies and change. The data collection is supported by Australia's Integrated Marine Observing System and data are open-access. Measurement(s) temperature of water • temperature of sea surface Technology Type(s) ocean time series station • satellite • ship-based water sampling • ship-based CTD profiles Sample Characteristic - Environment coastal sea water • sea water environment • continental shelf Sample Characteristic - Location Australia • Tasman Sea coastal waters of continental Australia • Western Australia [ABSTRACT FROM AUTHOR]

Identification and pairing of hydrologic events form the basis of various analyses, from identifying events for the calibration of hydrologic models, to calculation of event runoff coefficients for catchment characterization. Despite this, there is no unified approach for identifying hydrologic events. Here, using the R package, hydroEvents (https://CRAN.R-project.org/package=hydroEvents), we compare multiple methods of extracting and pairing hydrologic events focussing on the relationship between rainfall and runoff. We find the four common analytical approaches used to identify runoff events—based on either event threshold, local maxima/minima, or proportion of baseflow contribution, give similar results. However, when rainfall events are paired to runoff, the type of algorithm and the direction of pairing (either from rainfall to runoff, or runoff to rainfall) make a considerable difference to the final event pairs identified and resulting analyses. Here, we demonstrate the value of automated event extraction and pairing algorithms for large‐sample hydrology analysis by calculating event runoff coefficients across Australia. Our results show that climatology is a key driver of catchment rainfall‐runoff response with much of Australia dominated by excess rainfall runoff generation. However, our results also show that the variability due to pairing method can introduce a variability equal to that of the climatology due to biasing the runoff mechanism within the sample. With this analysis we demonstrate the importance of systematic and consistent approaches to hydrologic characterization when identifying and pairing hydrological events. [ABSTRACT FROM AUTHOR]

Cutoff low pressure systems have been found to be the synoptic system responsible for the majority of rainfall in southeastern Australia during the cool season (April–October inclusive). Meanwhile, rainfall in southeastern Australia at the seasonal and interannual scale is known to be related to remote climate drivers, such as El Niño–Southern Oscillation, the Indian Ocean dipole, and the southern annular mode. In this study, a new automated tracking scheme to identify synoptic scale cutoff lows is developed, and then applied to 500-hPa geopotential height data from the NCEP1 and ERA-Interim reanalyses, to create two databases of cool-season cutoff lows for southeastern Australia for the years 1979–2018 inclusive. Climatological characteristics of cutoff lows identified in both reanalyses are presented and compared, highlighting differences between the NCEP1 and ERA-Interim reanalyses over the Australian region. Finally, cool-season and monthly characteristics of cutoff low frequency, duration, and location are plotted against cool-season and monthly values of climate driver indices (oceanic Niño, dipole mode, and Antarctic Oscillation indices), to identify any evidence of linear correlation. Correlations between these aspects of cutoff low occurrence and the remote drivers were found to be statistically significant at the 95% level for only a single isolated month at a time, in contrast to results predicted by previous works. It is concluded that future studies of cutoff low variability over SEA should employ identification criteria that capture systems of only upper-level origin, and differentiate between cold-cored and cold-trough systems. [ABSTRACT FROM AUTHOR]