December 7, 2019 | Published by | , ,

Picture (above): Drought landscape at Peak Hill. Credit: Granny Bee Flickr (CC-BY-NC-ND-2.0).

Modelling drought is one of the most complex tasks in climate science. It is complex because drought usually starts with a lack of rainfall, so we need to start by asking why something (e.g. rainfall) did not happen. It is made even harder because extreme droughts are relatively rare and we have relatively few records across the 100 year instrumental record, and these records do not cover all of the areas that are susceptible to drought.

During the CLEX workshop in Hobart, the Drought RP co-lead, Michael Roderick pointed out that across NSW there have been many very dry winters in the instrumental record. However, all previous dry winters have been followed by a wetter winter and the accumulated experience of long-term agricultural enterprises would reflect that experience, i.e., if you get a bad winter then surely you will get a better winter next year. That experience has steadfastly held true since 1900. The current circumstance has now broken from that experience. Ranging from central NSW to southern Queensland, rural communities have now faced three dry winters in a row. The BoM defines drought based on rainfall deciles and you obviously have a 1 in 10 chance of experiencing rainfall less than the lowest 10% of previous years. Well to have three of those in a row assuming rainfall in each winter is independent, is a 1 in 1000 chance and yet that is what has happened.

With that background, it is clear that we are going to need a longer-term perspective if we want to separate natural variability from any human climate change imposed signal on drought. That is why work by Associate investigator Linden Ashcroft that seeks to recover centuries old observations is so valuable. Working with international weather data rescue initiative ACRE Linden was an author on a paper that describes an inventory of 4583 unique entries of weather data from 2250 locations around the world. The recent paper highlights key goals for data rescue groups and continues her Australian work that has led to the recovery of pre-instrumental meteorological observations from across the country that help to reveal the extent and impact of droughts in early settlement.

Drought research is a diverse topic and scientists like Martin De Kauwe are part of research that takes in situ measurements in real time that directly inform our climate models and improve representation of droughts now and into the future. Martin is part of the international first generation of free-air CO2 enrichment (FACE) experiments that will set up observation platforms in the Amazon forest and already has platforms in Australian eucalypt forests. These experiments reveal the response of vegetation to increased CO2 via the stomata on plant leaves as well as the important role that soil nutrients will have in mediating this response.

Those same stomata on plant leaves also respond to heat, atmospheric moisture and CO2 in different ways that directly influence photosynthesis and the impact of droughts. Research performed by CLEX and colleagues from Western Sydney University compared the response of stomata in climate models with observations from flux towers. They found that commonly used models – including the one used inside the Australian land surface model, CABLE – were unable to replicate observed decreases in photosynthesis and stomatal conductance. The researchers tested an alternative hypothesis and found that models may need to incorporate a non-stomatal limitation, that is – a down-regulation in photosynthetic capacity, to match observations.

Another improvement in models that can give us a greater insight into how droughts may change in the future turns on a metric used in climate impact assessments known as the Aridity Index. This Index is commonly used to understand future changes in aridity and describes the balance between supply (rainfall) and demand (evaporative demand of the atmosphere) In its current widely used form, the Aridity Index predicts that water losses from evaporation will outweigh increases in rainfall, leading to increasing aridity and expansion of deserts worldwide. However, over past decades, satellites have observed greening of the Earth’s vegetation while precipitation and river flows have increased in many regions. Our drought researchers and colleagues set out to understand this apparent contradiction, known as the “aridity paradox”.

It turns out that the widely used Aridity Index only considers one aspect of aridity – how dry the atmosphere is and predicts relatively drier atmospheres worldwide. However, when the researchers analysed climate model predictions of rainfall, runoff and plant productivity that more directly reflect landscape dryness, a different picture emerged. In the global average, climate models predict higher rainfall, runoff and plant photosynthesis globally, suggesting a globally averaged wetter future. Regionally, both increases and decreases are predicted. For Australia, climate models suggest increased plant productivity (because of elevated CO2) and possible increases in runoff. The researchers concluded that in the current implementation, the widely used Aridity Index was too simplistic to capture the many aspects that define landscape aridity, including the amount of rainfall, water resources and vegetation productivity, and is a poor indicator of future aridity changes.

That doesn’t mean a future world won’t be drier in some locations. A paper published by Ben Henley in Environmental Research Letters found that climate change was likely to put a strain on Melbourne’s water supply if global average temperatures were to reach 2°C above preindustrial levels. The paper highlighted how the water reserve would shrink and offered solutions that would help Melbourne maintain its water supply into the future.

Along with this research, the past four months have seen important achievements and accolades for our Drought researchers.

Martin de Kauwe along with colleagues was the recipient of two grants. The first grant for $450,000 focused on Eucalypt Futures: using functional traits to predict species distributions and responses to environmental change. The second grant from the US Department of Energy was for $320,000 as part of the ongoing FACE experiment noted above. Martin and colleague Daniel Falster were also awarded $15,000 by the Australian Academy of Science to host a Boden Research conference, that will promote research on the representation of eucalypt ecology and physiology in vegetation models with an overall aim of asking “What makes eucalypts distinct?”

Anna Ukkola was awarded one of the very competitive Discovery Early Career Researcher Award with the goal of increasing the predictability of seasonal droughts in the Bureau of Meteorology’s seasonal prediction system.

We were also delighted to see drought researchers pick up a range of awards. Chief Investigator and CLEX Director Andy Pitman was recently awarded the Royal Society of Victoria’s prestigious Medal for Excellence in Scientific Research. What makes it particularly remarkable is that this is one of the few times that a researcher based outside of Victoria has been awarded the prize. Further, Nerilie Abram was promoted to Professor and in more or less in the same week was awarded the Priestley Medal of the Australian Meteorological and Oceanographic Society. Gab Abramowitz was promoted to Associate Professor, a well-deserved promotion.

Associate Investigator Tim McVicar recently won a Chinese Academy of Sciences (CAS) President’s International Fellowship Initiative (PIFI) Distinguished Scientist award for 2020.  The award will involve 1-2 weeks intensive interaction with CAS Institute of Geographic Sciences and Natural Resources Research, CAS Institute of Tibetan Plateau Research, and CAS Institute of Remote Sensing and Digital Earth (RADI).

We were also delighted that Manon Sabot and Sanaa Hobeichi were part of UNSW Women in Maths & Science Champions group, which won the UNSW President’s Award for Embracing Diversity. During all of this activity we hosted international colleagues including Professor Dani Or from ETH Zurich who collaborated with Mike Roderick and Luke Parsons from the University of Washington who worked with Ben Henley.