Picture: Drought stricken landscape. Credit: Meruyert Gonullu (Pexels).

Understanding what causes droughts and what brings about their conclusion is key work in a dry continent like Australia. Often, we use computer models and modern observations to reach our conclusions but sometimes the clues to these questions can be uncovered in the past. To shed more light on past droughts, CLEX researchers took advantage of a newly released dataset from the Bureau of Meteorology to re-examine the infamous Centennial Drought of 1888. Using the new dataset along with historical station data, they analysed monthly rainfall variability across south-eastern Australia throughout 1888. They found declines occurred throughout the year, but particularly in April and early spring. The most severely affected regions were inland New South Wales and Victoria, as well as eastern Tasmania. To investigate what may have caused these exceptional declines they interrogated historical climate indices data, building an idea of what the state of the climate system was at the time. They found that a strong El Niño event in the equatorial Pacific Ocean likely drove the strong declines seen in the second half of the year, while the precipitation pattern throughout the year was modulated by a positive phase of the Southern Annular Mode in the Southern Ocean. An anomalous increase in the intensity of the subtropical ridge of high-pressure systems across the country may have also contributed to the low rainfall totals during 1888. This study has now added the 1888 Centennial Drought to our growing library of key events in Australia’s climate history.

Uncovering the causes of these past events helps give us insight into the circumstances that bring about modern droughts and how their occurrences may change in the future. Like the 1888 Centennial Drought, the decline in rainfall in a key agricultural region, the Murray Darling Basin, may also be linked to El Niño events. New research shows the variations within these events can also have distinct and significant impacts. Our researchers separated El Niño into central Pacific and eastern Pacific events to examine if the strength of a central Pacific event controls the rainfall amount for southeastern Australia. They found the stronger a central Pacific event is, the drier it is over Australia during the onset phase from April to September. But after October during the mature phase of El Niño, the strongest central Pacific events lead to more rainfall than normal over the Murray Darling Basin, whereas the weakest central Pacific events lead to less rainfall than normal. This relationship is strongest in January to March around the time that the central Pacific event is fully developed. For the strongest central Pacific events, this can be explained by a change in the circulation from drier, more westerly flow during the onset phase to moister, more easterly onshore flow during the mature phase. This finding is important for agricultural and water resources planning efforts in the Murray Darling Basin region and may help with seasonal prediction efforts to predict drought‐breaking rain such as occurred in early 2020.

Persistent droughts also have other impacts and there is little doubt that drought contributed significantly to the Black Summer bushfires of 2019/2020. Working with the Attribution and Risk research program, we investigated the climate-related factors that contributed to the unprecedented Black Summer fires and the ways that these factors are being altered by human-caused climate change. The study concluded that improving the methods used to adapt to the now inevitable increase in fire risk here in Australia, while also pursuing urgent global climate change mitigation efforts, was the best strategy for limiting further increases in fire risk. The authors warned fire disasters like the Black Summer were made worse by human-caused climate change in multiple ways; some of which are very well understood and some where more research is needed. These combined climate change impacts mean that bushfires are expected to rapidly become even more severe in southeast Australia.

While droughts undoubtedly have a widespread influence, understanding their impact on agriculture and ecosystems often requires a microscopic understanding of some plant processes. One of these processes is the exchange of gases at leaf-level in plants. Leaf level measurements provide us with an understanding of the physical processes that illuminate how plants trade carbon and water on daily timescales. Data from these measurements provide arguably the key constraint on simulated carbon uptake and transpiration from land surface models. These datasets allow us to scale-up leaf-level understanding via models and make predictions about plant responses to global environmental change. However, collecting these data are technically challenging, time-consuming, and individual studies generally focus on a small range of species, restricted time periods, or limited geographic regions. As part of an international team, our researchers proposed a reporting format for leaf-level gas exchange data and metadata to provide guidance to data contributors on how to store data in repositories to maximise their discoverability, facilitate their efficient reuse, and add value to individual datasets. Should this come to pass it would have an important influence on improving climate model projections.

Amid our research we have also seen a number of other remarkable successes. Martin De Kauwe was part of a team that was awarded a LIEF grant to setup Australia’s first critical zone observatory. These will be heavily instrumented sites measuring from the groundwater to the canopy and should be transformative for model evaluation/development. 

Nina Ridder had her paper, Global hotspots for the occurrence of compound events, listed in the Top 50 Earth, Environmental and Planetary Science Articles for 2020. The recognition is based on reader numbers with Nina’s paper being the 15th most read paper for the year. The paper also included CLEX authors Anna Ukkola, Annette Hirsch, Margot Bador, Jason Evans, Alejandro Di Luca and Andy Pitman.

But when it came to accolades, Jason Evans has had an impressive few months. He started the year on a high note when he was unanimously voted as a Fellow of the Royal Society NSW. Then he was named as a fellow of the Modelling and Simulation Society of Australia and New Zealand Inc. The fellowship recognises those who have shown unselfish dedication to promoting the aims of the Society, and for significant contributions to modelling and simulation.

He has also been active in outreach, presenting a webinar on Impacts of climate change on extreme event hydrology for the Australian Water School, where attendees were largely practising engineers. He also took part in the meeting National First Peoples Gathering on Climate Change, organised by the NESP Climate Change and Earth Systems Hub. It brought together scientists and indigenous people from all around Australia to discuss the impacts of climate change on country, what changes we might expect in the future and how we might adapt to them. Finally, we welcome two new students to the Drought program, Anton Steketee and Hana Camelia who will be working with the Drought program co-lead Nerilie Abram.