March 21, 2019 | Published by |

We welcome new PhD Student Lina Teckentrup and Masters student Mustapha Adamu.

A recurring theme with the Drought program is that small changes can make a big difference. An example of this is the relationship between radiation, evaporation and surface temperature, over wet surfaces, which has been an area of intense study for 50 years. This relationship is important for for estimating evaporation from saturated land surfaces.  To test a new formulation they developed to explore this relationship, CLEX researchers used newly available satellite data for radiation to investigate how radiation, evaporation and temperature interact over the global oceans.  The results showed that at global and local scales the observed evaporation from the oceans occurs at the maximum possible rate.  They suggest that the concept of a maximum in the evaporation from the ocean is a natural attribute of any extensive wet evaporating surface. This work has provided fundamental new insight into how radiation, evaporation and temperature are interlinked over very wet surfaces and may provide deeper insight into evaporation of saturated surfaces on land.

Continuing the theme with work on fundamental processes, an international team including CLEX researchers found that a process known as mesophyll conductance had a significant impact on how plants respond to increase carbon dioxide levels. This not only affects plant growth but also carbon and water exchanges. Importantly, mesophyll conductance is not currently included in climate models. Whether or not the mesophyll conductance changes how climate models project regional changes in climate remains to be seen, but this is an important first step in ensuring our models represent all of the key processes properly.

Research on photosynthesis processes was also key to the development of a new algorithm that will help improve prediction around the the function of ecosystems in the future as regions experience climate change. It has long been known that plants can adapt to variations in temperature, either permanently through genetic evolution or through short-term, reversible temperature responses. However, this ability to adapt in these two ways has proved difficult to conceptualise in an algorithm that could be used in climate model applications.  A new multi-institutional collaboration involving CLEX researchers has been able to show how to include current knowledge in a suitable algorithm. This research will help agricultural and ecosystem researchers understand future vegetation changes with global warming and has the potential to be included in climate models in the form of a vegetation feedback.

Vegetation responses to a changing climate were also the key to a paper that found droughts may not increase as a result of climate change. This finding resulted from researchers investigating an apparent climate model contradiction. This contradiction sees climate change projections of the 21st Century that showed increasing droughts (calculated using off-line climate impact models) with more run-off and a general greening of the landscape. This work, published in Nature Climate Change, showed that the off-line climate impact models had not factored in how vegetation growth and water use responds to increasing atmospheric CO2. Once taken into account, researchers found that climate impact models project a warmer future with more vegetation but little change in droughts in line with some current climate model projections. However, as we have noted in previous work, current climate models do not simulate drought processes well, so whether droughts increase or decrease with increasing atmospheric CO2 remains an open question.

In another paper looking at fundamental processes, CLEX drought researchers worked with colleagues in the rainfall program and examined the long asked question of whether rainfall followed wet soils. The researchers found that the amount of moisture already present in the soil could alter precipitation both in the north and south of Australia. Intriguingly, while in the north wetter soils produced more rainfall, the opposite occurred in the south. These results further demonstrate the complexity of coupling between the land surface and the atmosphere and adds to the difficulty in providing accurate regional projections of future climate change over Australia.

We also continued our work on developing new observation-based gridded databases that can be used for model evaluation and development. At the land surface, energy and water are coupled via evaporation and this is central to linking rainfall and runoff with radiation, humidity and temperature. To that end, CLEX drought RP researchers have produced a dataset that increases the accuracy of global river flows by developing a re-analysis type product based on assimilating available hydrologic and meteorological data. We expect to make increasing use of this important baseline data in coming years.

Finally, the Drought team has also tested and improved a dataset for land degradation over Australia and found that the new dataset reduced the uncertainties for Australia. A previous version of the dataset had caused significant errors in trends over some of Australia’s dryland regions because of problems in calibrating the satellite images. These problems have now been corrected after the researchers identified and accounted for the data artefact that caused the errors in the updated dataset. It is recommended that this new version be applied globally. Further details can be found in the associated paper, here.