August 1, 2019 | Published by |

Picture above: Dry River by Chris Fithall. (Creative Commons Flickr).

As this newsletter goes to press, Bureau of Meteorology rainfall records show most of NSW and substantial parts of south-west Queensland remain in drought. Beyond the immediate agricultural, hydrologic and ecologic impacts, many small rural towns are starting to run out of water. This NSW-centred drought is biting hard! Whether this drought is just of repeat of past events or is unique remains a hot topic of scientific dialogue amongst Centre researchers as we continue to seek to unravel the causes and consequences.

The Drought team welcomed a new associate investigator, Linden Ashcroft, to our University of Melbourne hub. Linden is an expert in historical weather records and will be using documentary records and paleoclimate data to explore the droughts of the past, their causes, and how they may change in the future.

Another associate investigator affiliated with both the drought and heatwaves programs, Joelle Gergis, took an interesting step outside of direct research to co-curate an art exhibition titled Water, soil & life, at the Charles Nodrum Gallery. Each of the pieces on display looked at the variability of Australia’s climate from settlement to today. The art works were combined with passages from Joelle’s recent book, Sunburnt Country: The future and history of climate change in Australia.

One of the key lessons of the Drought programs research is that small changes in the representation of key soil and vegetation processes can have large impacts. As a result of this, we often find ourselves investigating the assumptions used in climate models to determine if those assumptions are consistent with new process-based understanding of these small-scale soil-vegetation processes.

Recently, we used the Comins and McMurtrie analytical framework to determine if the influence of soil nutrients on the carbon dioxide fertilisation effect was accurately reproduced in a range of climate models. Using this framework allowed us to unlock insights into the representation of plant nitrogen uptake. Overall, our results highlighted the fact that the quasi-equilibrium analytical framework was effective for evaluating both the consequences and mechanisms through which different model assumptions affect predictions.

One important area where errors can creep into modelling outcomes is through misclassification in the assumed land cover. Our researchers examined whether simulations of air temperature and rainfall were impacted in areas where there was a low accuracy for land cover classification, with a particular focus on East Asia. The results showed that misclassification‐induced land cover change does affect key biogeophysical characteristics (albedo, leaf area index, and roughness length) that modify the sensible and latent heat fluxes at regional scales. However, we found that the impact on regional air temperature was very limited and was restricted to the Tibetan Plateau where warming of up to 2 °C occurs associated with the replacement of barren or sparsely vegetated land with grassland. The impact on regional rainfall was negligible.  Overall, we concluded that uncertainties in the reconstruction of land cover have negligible impacts over the south-east Asian region and that we can use standard satellite-based products (i.e., the Moderate Resolution Imaging Spectroradiometer land cover product) to specify the land cover in regional climate simulations over East Asia.

Another area that requires a better understanding is the impact of climate extremes on crop yield. Working jointly with the Heatwaves and Cold Air outbreaks team, a team of international researchers looked at the response of four staple crops — maize, wheat, rice, and soybeans — to determine how the yield was impacted by extreme climate events. Intriguingly, they found that seasonal heat extremes were more important than precipitation extremes when it came to yield impacts for these crops. The only exception to this finding was in southwest Western Australia, where precipitation variability played the leading role in yields of spring wheat.

A key part of understanding the impact of droughts now and into the future is to accurately determine at what stage they produce tree mortality. Working with colleagues from the Hawkesbury Institute for the Environment, Centre researchers examined eight species of eucalypt to determine how long it would take for these trees to completely dehydrate under drought conditions. The variation was considerable, between 96 and 332 hours. This research is a start on improving our ability to predict the timing of drought-induced mortality at tree and forest scales.