March 22, 2019 | Published by |

Even with the holiday break it has been a busy time for the research program with visitors, awards, public engagements and new arrivals.

Dr Caroline Bain from the UK Metro Office visited CLEX to work with Michael Reeder on research into novel techniques to track high impact weather in tropical regions.

We also welcomed Eric Oliver a new Associate Investigator specialising in marine heatwaves and new students, Ritwik Misra, Jemima Rama and Jingwei Zhou.

Meanwhile, we were pleased to see Associate Investigator Andrew King win the inaugural AMOS award for Science Outreach. Assoc Prof Julie Arblaster also made the Clarivate Analytics list for consistently most highly cited researchers in their field over a 10-year period.

Chief Investigator Michael Reeder was a panel member of a free public lecture associated with AMOS Fire Weather Workshop, A decade on: lessons from Black Saturday. In this role, he spoke about what we have learnt in the past 10 years about the science of bushfire weather, including the development of a coupled atmosphere-fire version of the Unified Model. Earlier in the day, Michael and Todd Lane both gave talks at the AMOS Fire Weather Workshop.

But it is in research where we have seen the most new developments. Over the past four months, we have seen a lot of research crossover between ourselves and the Drought RP as we combined to produce four papers. Of these papers, three were focused on model improvements, as successfully modelling future droughts and future heatwaves tends to encounter similar obstacles.

One of the fundamental influences on climate model projections in this area is to understand which models to choose. In a Nature Climate Change paper, CLEX authors and colleagues suggested moving away from an approach that determines models purely on their ability to successfully project future climates. Instead they suggested model selection should be based on analysing the performance patterns to understand the processes that make some models more successful than others.

In a review paper for Earth System Dynamics, CLEX researchers as part of an international team explored how models that used almost identical processes would naturally produce very similar results, known as “model dependence”. The authors questioned whether these results were robust if they were based on similar processes and suggested approaches to avoid overconfidence in model outcomes and how to avoid this model dependence to produce more robust results.

This approach was explored in another paper that looked at the impacts on variations in seasonal precipitation and the soil moisture/temperature response and how these were represented in climate models. It found that where these relationships were unrealistically represented there was an over estimate on future extremes. Excluding these models reduced the uncertainties around future changes in extreme heat events.

High-quality data is important for testing our models. So, CLEX researchers looked at a land degradation dataset, GIMMSv3.0g, where Australian researchers identified calibration errors that had caused significant errors and trends over Australia’s dryland regions. It is likely that these errors have affected previous estimates of dryland degradation globally. A recent update to the dataset, GIMMSv3.1g, was tested and appeared to remove these errors. It was recommended the research community use this latter dataset and noted that using multi-ensemble runs with different datasets produced a more comprehensive understanding of uncertainties.

CLEX researchers also looked at the Coordinated Regional Downscaling Experiment (CORDEX) to test the accuracy of its regional projections against temperature and precipitation. They noted some unique errors with individual model members but overall it produced a good average representation of Australia climate.

This continued focus on the improvement of climate models is key to understanding how extreme events may change and how we as a community can respond. Recent research led by PhD student Cassandra Rogers found that during heat waves the overnight temperatures between three Australian cities and the country areas around them can vary by as much as 3.3°C. The results of this investigation suggest adaption measures will need to be taken as Australian cities expand and extreme heat events become more common.

Understanding the processes that lead to heatwaves can also help us improve our forecasting around them. This was shown in a paper that examined how the El Niño Southern Oscillation (ENSO) impacted Australian heatwaves. In revealing how land surface processes responded to ENSO events they found that this was most important in the northern part of Australia and that this finding could help improve forecasting of heat waves in this region. The ENSO relationship was less important in south-eastern Australia.

Seraphine Hauser, a student from Karlsruhe Institute of Technology (Germany) supervised by Julian Quinting (a former postdoc in the ARC Centre of Excellence for Climate System Science), visited Michael Reeder and Shayne McGregor for 3 months. During her visit, Seraphine worked with Michael and Shayne on a synoptic perspective on the effect of ENSO on cool season rainfall in southeastern Australia.

Finally, there continues to be significant work on marine heatwaves particularly around Australia. The heatwaves team carried out a piece of fundamental research that categorised marine heatwaves on a scale similar to that used for tropical cyclones. This was important for communicating these marine heatwave events and providing a global standard for describing the events as they develop.

The importance of this work was demonstrated with a paper in Nature Climate Change that highlighted how ocean heatwaves were completely reconstructing ecosystems. These ecosystem changes persisted even after the waves had ended, creating what was described by the authors as an ecological-step change. The work in this area by CLEX researchers continues to be at the forefront of marine heat wave research and has already produced outcomes that will help us to improve our forecasts of marine heatwaves around Australia.