Special Issue "Australian Hydroclimate Extremes in a Changing Climate"

Dear Colleagues,

Australia has become a hotspot of hydroclimate extremes and compounding hazards that trigger severe social distress in impacted communities and huge revenue losses. Some recent examples are the widespread 2021-22 flooding in the East Coast preconditioned by triple-dip persistent rain induced by La Nina and saturated catchment conditions, and the unprecedented 2019-20 Black Summer bushfires caused by concurrent drought and extreme heat combined with high wind and dry fuel loading. Given the exposure to frequent heatwaves, droughts, floods, bushfires, and cyclones, which are projected to intensify in a warmer climate, such cascading events will become more prevalent under climate change. However, scientific understanding, based on the complexity of identifying, simulating, predicting, or attributing the changes of such cascading events under climate change, remains limited. This Special Issue of Atmosphere aims to collate the contributions from hydrology and climate science communities on recent research advances in hydroclimate events and their impacts in regional Australia from compounding hazards in a changing climate.  Original research articles on key characteristics and regional impacts based on observations, novel techniques (including machine learning), and underlying physical processes (including ocean–atmosphere–land interactions, hydrological/water cycles, climate modeling, event attribution, and CMIP-style future projections across various spatio-temporal scales), among other things, are invited.

Dr. Sur Sharmila
Guest Editor

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• compound events
• climate change
• extreme event attribution
• hydroclimate extremes
• hydrological cycle
• land–atmosphere interaction
• regional impacts

Title: Australia's changing hydroclimate extremes: from the past 100 years out to 2100
Authors: Wendy Sharples; Ulrike Bende-Michl; Sharmila Sur; Navid Ghajarnia; Steven Thomas; Zaved Khan; Elisabetta Carrara.
Affiliation: Bureau of Meteorology, Australia
Abstract: Dorethea Mackellar famously wrote in her poem "A Sunburnt Country" that Australia was a land of droughts and flooding rains. But has that really always been the case and are these droughts and flooding rains set to increase due to a warmer world? We use a state-of-the-art seamless hydroclimate dataset - the Bureau of Meteorology's Australian Water Outlook - to chart Australia's past to present to projected hydroclimate fields to track the changes in rainfall, runoff, and soil moisture conditions, to understand what the hydroclimatic future holds for Australia if we continue along the current emission scenarios. Compared to the past, hazardous events such as bush fires and floods are currently increasing, with rainfall distributions changing along with an increase in temperature. Presently, many regions are cycling through hazards sequentially taking additional tolls on an already strained community. In the future, more regions will be subject to droughts with longer durations, resulting in impacts such as more intense fire seasons and food bowl challenges such as crop and livestock stress. Heavy rainfall events are projected to increase, presenting challenges for emergency services and water management including extreme river flows, flooding and dam overflows. With Australia's hydroclimate extremes changing, Australia's population will need to rapidly adapt to a new normal.

Title: Unveiling the future of Australia's water resources in a changing climate: key insights from the National Hydrological Projections
Authors: Ulrike Bende-Michl; Wendy Sharples; Vjekoslav Matic; Louise Wilson
Affiliation: Bureau of Meteorology, Australia
Abstract: Australia has one of the most variable climates on earth and its climate is changing rapidly: temperatures are increasing and precipitation patterns are shifting. On average, Australia has warmed by 1.44 ± 0.24 °C since national records began in 1910. Streamflow has changed across the country, broadly increasing in the north and decreasing in the south. Along with this observed decline in precipitation, streamflow has declined substantially in both the south-west and south-east, in regions of several major population centres; changes in streamflow are typically disproportionally larger than changes in precipitation. With rising atmospheric greenhouse gas (GHG) concentrations, temperature increases are projected to continue and intensify in the future, causing further changes in all components of the climate and hydrological system, including the faster drying of the land surface with increased evapotranspiration and soil moisture depletion across catchments. Given many Australian communities, businesses, governments and environments already experience periods of limited water availability, in the context of increasing demands from water, these changes represent ongoing challenges to the management of Australia’s water resources. To ensure that future water needs are met, decision-makers need access to hydroclimatic projections data, guidance, and robust scientific knowledge to adapt to a range of conceivable futures. The National Hydrological Projections (NHP) product, recently released by the Bureau of Meteorology as part of the Australian Water Outlook suite, uniquely provides nationally consistent water information. It can complement local projections funded by State Governments as well as be a source of information where local modelling has not yet been performed. NHP can underpin strategic decision-making processes for future water resource management, adaptation and water policy developments. It consists of nationally consistent hydrological projections datasets, which allows for rapid and computationally inexpensive assessments of changes to future hydro-climate conditions at desired multiple spatio-temporal scales. Available information and guidance materials allow users to develop their own insights that are sensitive to the limitations of the data and scientifically sound. Based on the NHP dataset, we detail plausible future water resource changes for Australia, and demonstrate how specialist user guidance for meaningful application of data and associated knowledge is translated into useful and actionable intelligence in water resource management.