April 1, 2020 | Published by |

Picture: Dry landscape. Credit Olivier Mesnage.

The drought may have eased over parts of Australia that received rainfall in late January but that doesn’t mean our research into these extended dry conditions has also declined. In fact, the extensive drought that affected much of eastern Australia over the past few years has added a great deal to our insight into their causes, impacts and importantly how they draw to an end.

New research suggests that instead of looking at what causes droughts, it may be far more useful to understand why widespread drought-breaking rainfall fails to appear over extended periods. Using Australia’s more than century-long observational record our researchers found that drought-breaking rainfall in south-eastern Australia primarily corresponded with negative Indian Ocean Dipoles (IOD) and La Niñas. Similarly, the likelihood of a drought occurring over the Murray Darling Basin and south-east Australia went up according to the length of time between either negative IOD or La Niña events. This suggests that if we look at how future droughts may change over these parts of Australia, understanding how climate change affects the frequency and intensity of these phenomena will be key to these projections.

As Australia experiences droughts on a relatively regular basis, our research also extends to understanding how they affect our native vegetation and agricultural crops. A recent analysis of impacts focusing on the Millennium Drought found cultivated lands and grasslands were most sensitive to drought conditions and experienced the most severe impacts. The impact on natural vegetation varied, with it being more robust to drought conditions in areas of high humidity and more sensitive in arid landscapes.

To understand drought better, we also need to understand how water moves through the terrestrial environment. Despite widespread interest in hydrologic variability, there is currently no general climatology of the variability of the water cycle over land and this has limited the development of the underlying science of hydrologic extremes. In an effort to develop a climatology, our researchers used a recently published global hydrologic reanalysis (1 degree, 1984-2010) to present, for the first time, a global climatology of hydrologic variability. The results highlighted the challenges of developing such a climatology, revealing that the variability in streamflow was often greater than the variability in rainfall, while surprisingly, there was much lower variability in the amount of water released by plants through evapotranspiration.

The impact of either too much or too little rainfall on vegetation is an area of research of importance to natural and agricultural environments. Comparing observations to global models, drought researchers found that in the short term – periods of up to a month – the models worked well but were less capable of capturing annual responses to rainfall variation. In addition, while the models were very good at reproducing the response of vegetation to a lack of rainfall, they overestimated vegetation response to increased rainfall.

Focusing on Australian modelling capability, the Drought program analysed the latest version of Australia’s Community Atmosphere Biosphere Land Exchange (CABLE) model coupled with Weather Research and Forecasting (WRF) model for regional applications. The analysis did not identify one configuration that consistently performed the best for all diagnostics and regions. Results were strongly dependent on the region of interest, with the northern tropics and south-west Western Australia being more sensitive to the choice of physics options compared to south-eastern Australia, which showed less overall variation and overall better performance across the ensemble. Comparisons with simulations using the Unified Noah land surface model showed that CABLE in NU-WRF had a more realistic simulation of evapotranspiration.

Working with the Heatwaves and cold air outbreaks the Drought program produced research that generated a new cross-scale modelling framework for urban environments that has been applied to calculate how electricity and gas demand will change under future climate change and air conditioner (AC) ownership scenarios. Our researchers used Melbourne as a case study capturing interactions across building, urban and atmosphere scales at a higher temporal resolution than any location worldwide. The framework can undertake century-scale simulations. The climate modelling systems resulting from this study are open-source and model outputs are also available across the century at half-hour timesteps.

Adding to our research team, we welcomed Jon Page who has just started a PhD with Gab Abramowitz and Martin de Kauwe (RP3). Jon will be looking at vegetation responses to elevated CO2, in particular, how water availability limits the growth response.

As well as doing research, some of us were able to fit in conferences and workshops before the pandemic started. Martin De Kauwe attended the Manipulation Experiment Synthesis Initiative (MESI) Workshop in Auckland. The workshop focused on research carried out over three decades, where scientists carried out ecosystem-scale manipulation experiments to understand and predict future responses of the carbon, water, and nutrient cycles to global environmental change. These experiments are one of the key constraints we have on global climate models predictions and yet models have grossly under-utilised these data when evaluating predictions. We now have over ~2000 of these experiments and the aim of the workshop was to synthesise existing experimental databases to create a single unified database. It is hoped this database will allow us to explore pressing global change questions and better evaluate model predictions in the future.

Beyond the immediate research, it gives us great pleasure to acknowledge the successes of one of our own. Nerilie Abram has had an impressive few months, being awarded the Priestly Medal by AMOS, winning an ANU Vice-Chancellors award and being promoted to a full professor – all well-deserved honours. Finally, we can’t help but draw attention to the new Cranky Uncle climate change app being developed by communication expert and founder of Skeptical Science John Cook. Cranky Uncle is a smartphone game that uses cartoons and gameplay to interactively explain the techniques used to cast doubt on climate science. It also uses caricatures of climate scientists and we have it on good authority that our program leader and CLEX Director Andy Pitman has had his likenesses added to the collection. We look forward to seeing a copy of the original hanging on his wall sometime soon.