Research has now begun in earnest in the Drought Research Program with all key staff finally in place. This has proved timely. At the time of writing (August 2018) most of NSW has been drought declared and forecasters suggesting little sign of drought-breaking rains over coming months. Rural communities throughout eastern Australia are feeling the strain and the NSW government has recently made more than a billion dollars of emergency funding available.
We are responding to evolving events and hope to have something to say on the current eastern Australian drought over coming months. Watch this space!
We congratulate Dr Yuting Yang who was awarded a 2018 Kamide Lecture by the Asia Oceania Geoscience Society. Yuting presented his lecture at the annual meeting, held this year in June at Honolulu. Dr Yang will shortly depart Australia to begin a tenure-track position at the prestigious Tsinghua University in Beijing. We wish him and his family well and look forward to Centre researchers continuing their collaborations with Yuting over the coming years.
We also congratulate CLEX Director and Drought RP co-lead, Prof Andy Pitman, who has been recognised, yet again, with a Eureka Prize nomination for Leadership in Innovation and Science.
Since our last newsletter, our research has proceeded on three fronts involving:
- collaborative studies on process based field studies relevant to drought that focus on the underlying processes,
- model evaluation studies, and
- new work on community resilience to climate extremes.
1. Drought Processes
Leaf Area Index
Several recent model comparisons have shown large disagreements among models, compared to satellite-based estimates of the leaf area index (LAI). LAI is a key structural attribute of vegetation and central to understanding how vegetation interact with the atmosphere.
Bringing together observations and models, CLEX in collaboration with researchers at Western Sydney University tested a long-standing hypothesis (dating back to the 1980s), that LAI is dictated by the long-term water availability. The researchers used long-term climate data to test this hypothesis. Using this ecohydrological theory they made predictions of “equilibrium” LAI across Australia, and compared the results with satellite-derived estimates. These results showed a high level of consistency between their model predictions and ground- and satellite-based measurements.
They also made successful predictions about how LAI should have changed with recent (1980-2010) changes in atmospheric carbon dioxide concentrations and the results clearly demonstrate some fundamental principles of how vegetation interacts with the atmosphere.
Plant growth response to environmental change
Another cornerstone of current land surface models relates to the carbon balance of vegetation and how that might respond to ongoing increases in atmospheric CO2. Existing climate models account for these processes but the foundations of the climate models has proven difficult to evaluate due to the lack of field-scale observations.
Working with colleagues at the Hawkesbury Institute for the Environment and Colgate University, we applied a novel data assimilation approach to accurately predict plant growth responses to environmental change. Current models couple growth with photosynthesis. However, if the carbon storage capacity of plants is limited this relationship is expected to break down.
The new analysis was able to infer that the imposed limitation not only led to a reduction in photosynthesis but also a reduction in the rate at which stored carbohydrates were used. Approaches like this one will facilitate improvements in the process understanding embedded in models used to predict responses of the carbon cycle to climate change.
Why drought impacts differ
The Amazon experienced a once-in-a-century drought in 2005. In 2010 it was again struck by an even worse drought.
However, not all droughts are the same. The 2005 drought had a very high rate of tree mortality despite the fact that the 2010 drought was considered worse. We wanted to know what caused the different outcomes.
The answer was found in the lead up to the dry season, particularly the transitional period from the wet-to-dry season (May-July). In 2005, this transition period was considerably drier than normal, whereas in 2010 the amount of rainfall during the transition was only slightly below average. This meant there was more water available in the soil during the drought period in 2010 than in 2005. Hence even though the dry season drought of 2010 was worse, the tree mortality and reduction in carbon uptake was smaller than in 2005.
2. Model Evaluation
Extremes bias in models
Climate models are extremely useful tools for investigating how the climate might change. Until recently, most emphasis has been on changes in the long-term averages but in CLEX our interest has moved to extremes. There is much less experience in using climate models to project extremes.
One of the difficult problems is that individual climate models show bias (compared to observations). In studies of the changes in long-term averages, those biases generally cancel out when we take an ensemble across different models. However, the same does not happen when trying to project extremes and we need to make bias-corrections to the outputs from individual models. The best way to do that has not yet been established.
Along with colleagues from Lawrence Berkeley National Laboratory, CLEX researchers aimed to test a new bias correction scheme. The results showed that the new method did improve projections of extremes but the researchers also found that it was critical to account for changes in the long-term mean when making these projections.
Comparing drought across models
There is a widespread perception in the broader community that droughts will increase because of future warming but there is little evidence to support this idea.
With that in mind, CLEX researcher, Dr Anna Ukkola recently led a team who evaluated global climate models for common drought metrics during the past 55 years. They found that different climate models can produce very different simulations of drought. The researchers found that model differences relate strongly to how the models represent the land-atmosphere interactions at the surface. The study points to a clear need to improve climate model projections of hydrologic extremes to reduce uncertainties in future projections.
Preparing for catastrophe
One of the key aspects of droughts and many other extreme weather events is the impact they have. CLEX, together with an international team, suggested in a Nature Climate Change article that a new approach is needed to interpret and manage risk around catastrophic weather events. The approach they put forward was similar to stress testing a business and is based on the idea that it is the confluence (or totality) of events that is critical.
For example, in 2012, an unusual confluence of weather systems resulted in Hurricane Sandy taking a sharp left turn towards New York and New Jersey. As Sandy made landfall it coincided with a high spring tide, leading to the highest storm surge for the region in 300 years. It left 233 dead and US$50bn damage. The key point was that it was a combinations of factors, and not a single factor, which amplified the destructive nature of this event.
The traditional approach to evaluating such risks begins with a (climate) scenario. The new research advocated a shift towards examining the total system.
As an example they suggest looking at the possible meteorological drivers that would lead to a citywide power outage. This would mean examining the climate-sensitive elements of the power system such as renewable power resources or physical assets like poles and wires that could be affected by heavy winds, lightning and flooding.
With this knowledge as the starting point, it becomes possible to understand what confluence of climate hazards could influence the system and then look at the likelihood of these occurrences. It also gives business and infrastructure experts insights into where the most effective changes can be made to build climate resilience into a system.
The researchers describe the difference between the two approaches as a “shift from impact analysis to vulnerability analysis”.