March 23, 2019 | Published by |

In mid-December, chief investigator co-leading the extreme rainfall program, Todd Lane, was named as an AMOS Fellow and chief investigator Christian Jakob was awarded the 2018 Morton Medal.

Continuing with the research program’s winning ways, student Pavan Harika Raavi received the John and Allen Gilmour Award from the Melbourne University faculty of science, which aims to highlight medical or scientific research that benefits mankind.

The rainfall program’s research was also highlighted when the work of Claire Vincent featured on the cover of the NCI Annual report. The image is of a high-resolution animation taken from Claire’s impressive MJO study that looked at its influence on rainfall over the Maritime Continent.

Meanwhile, Associate Investigator with the Extreme Rainfall Program, Dr Joshua Soderholm was an invited by The Royal Society of Victoria to present his work on severe weather. Dr Soderholm has also recently returned from Argentina where he performed field research on severe hail events.

We also welcomed Dr Martin Jucker and Andrew Marshall as Associate Investigators to the extreme rainfall program. Other new arrivals to the rainfall program include Dr Yi Huang (Lecturer University of Melbourne) and Dr Stacey Hitchcock (Postdoc at The University of Melbourne).

But among all the awards and arrivals, it has been a very active period for research in the Extreme Rainfall RP with a continuing focus on understanding the strengths and weaknesses in current models to help clarify how high precipitation events may change in the future.

In December, CLEX research published in the Journal of Climate compared a suite of 27 CMIP5 climate models to determine if they gave a consistent signal for how extreme rainfall may change under a warming climate. The results were robust, with an increase outside the range of natural variability in the intensity of extreme precipitation events over the majority of land areas.

Understanding the processes that led to these changes in extreme rainfall and how they can best be represented in climate models is a continuing area of research for the extreme rainfall program. Exploring the dynamic components of these changes, CLEX researchers found that atmospheric convergence lines played an important role to changes in precipitation. The implications of this research, published in Geophysical Research Letters, suggest weather timescales will be needed by climate models to tease out the dynamic component of future changes in extreme rainfall.

Another key to improving the performance of models both in long-term climate projections and simulation of extreme weather events is through data assimilation techniques. Two recent papers have highlighted techniques that can reduce the uncertainty in observations. The first paper showed how to optimise certain data assimilation schemes to reduce observational uncertainties, while the second investigated an improvement suggested by partner researchers and found that it significantly improved forecast accuracy.

While these are extremely technical papers they result in improvements that are already having impacts on what we understand about extreme rainfall events now and into the future.

In a recent piece of cross-program research working with the Drought program, we found that the wetness of the ground can have a direct impact on how much rain falls. Focusing on Australia, the researchers found a strong link between soil moisture and rainfall but in completely opposite directions for the north and south of Australia. There is a suggestion that as climate models increase their resolution this coupling between the land and atmosphere may be considerably different to what has been previously estimated.

But is not just the soil that can influence extreme rainfall events. To the north of Australia in the Maritime Continent recent research found the important role topography can play. Investigating flood events around Jakarta, Indonesia, it was found that the Indian Ocean Dipole played a greater role in extreme rainfall events than El Niño. The results suggested this was a direct result of local topography, which created very localised responses to large-scale conditions.

How rainfall forms has also been revealed to have an impact on rainfall events when CLEX researchers compared systems with organised convection to those with unorganised convection. Surprisingly, they found the instantaneous rain rate did not change between two forms of convection but that organised convection still produced more rainfall because it stayed for longer periods over a single area.

A well-known, regular and structured storm in Darwin — colloquially known as Hector the Convector — was the focus of a study that looked at how strong updraughts from storms brought moisture into the stratosphere. The study refined our understanding of these updraughts and found that many of them did not actually bring moisture to this part of the atmosphere.

Finally, another observational study looked at hybrid cyclones around Australia focusing on two examples in South Australia that led to storm force winds and damaging storm surges. Both these examples had significant impacts on infrastructure. Hybrid cyclones are relatively cold in the upper troposphere like a typical extra-tropical cyclone and warm in the lower troposphere like a tropical cyclone. The researchers found that they primarily fall from May to September usually over the Tasman Sea or Great Australian Bight. The researchers were able to use models to understand the characteristics of the cyclones revealing where the strongest precipitation occurred and the processes that led to the formation. These processes were similar to those we find tropical cyclones.