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By Asaesja Young 13 December 2017 3 min read

Image: Flickr/Monica Mitrione

ON Monday 21st November 2016, a thunderstorm swept through Melbourne.

The spring storm developed over the day, and in the late afternoon, severe storm warnings were issued, predicting damaging winds, heavy rainfall and large hail.

In a process that is not well understood, microscopic pollen particles from a common European ryegrass, interacted with the storm system and were transported across Melbourne, causing thousands of people to develop breathing difficulties over a very short period of time.

For many of those affected this was their first asthma attack.

As a result, Victorian hospitals saw a 681 per cent increase in asthma-related admissions from 6pm on the 21st to midnight the following day.

Ten deaths are potentially linked to the event and are being considered by the coroner’s court.

Using a system built by CSIRO and the Bureau of Meteorology (BOM) to forecast the movement of noxious atmospheric particles caused by fire, researchers are working to understand and forecast how ryegrass pollen moves through storm systems.

It is a complicated task that requires expertise from many institutions including the Victorian Government Department of Health and Human Services, BOM, CSIRO, University of Melbourne, University Technology Sydney, Queensland University of Technology, and UTas.

The team is five months through a three year project which they hope will deliver a detailed forecasting and alert system for Victoria and Tasmania.

Explaining the conditions behind thunderstorm asthma

Leading the pollen transport component of the work, CSIRO scientist Dr Kathryn Emmerson, said her team was working to understanding how pollen is dispersed under different environmental conditions.

rye grass pollen rupturing under a microscope
Ryegrass pollen granule rupturing. Image: Deakin University

"We’re working to explain how pollen moves from the plant and into the air, where it goes, where it lands and how it might interact with different weather systems including storms,” says Emmerson.

"Ryegrass pollen is 35μm in diameter, which is about a third of the width of one human hair, and it has a density similar to water.

"Under certain conditions, these tiny particles of pollen rupture, releasing hundreds to thousands of minuscule starch granules into the atmosphere. It is these granules that experts believe are responsible for the allergic response experienced during asthma storms.

"The tool uses land-use maps which show where these grasses grow, and then incorporates variables such as wind speed, temperature and relative humidity to predict how pollen particles move under different conditions.”

Average pollen concentrations, Victoria. Image: Kathryn Emmerson

Project leader and BOM scientist Dr Beth Ebert, said there were many unknowns when it came to thunderstorm asthma.

"The science of thunderstorm asthma is relatively unknown, and what is least understood is the interaction between pollen and thunderstorms,” says Ebert.

"At the moment, we don’t know enough. We think the basic ingredients needed are high ryegrass pollen concentrations and thunderstorms, but there appear to be previous instances where high winds, and not storms were the involved.

"The good news is, we have some great minds from a number of Australian research agencies working on the problem and considering a raft of factors including what conditions influence high pollen growth, timing of pollen release, and what causes the pollen to rupture.”

The team is using satellite data from Himawari-8 and time-lapse cameras on the ground to develop a spatial understanding of ryegrass by tracking when areas become more and less green and how that change correlates with the release of pollen.

A new forecasting system

This year the Victorian Government worked with a number of partner organisations, including the Bureau of Meteorology and Melbourne and Deakin universities, to develop and deploy a forecasting system for epidemic thunderstorm asthma.

The system is built on statistical analysis and manual pollen counts from several stations across Victoria, including five new pollen monitoring sites. The pollen data is overlaid with BOM’s thunderstorm forecasting to provide a low, moderate or high forecast. The forecast is issued by the Victorian Department of Health and Human Services during pollen season (October to December).

"We will run the new system in testing mode for the 2017 season, and in real time during the next pollen season, alongside the current system,” says Ebert.

"This comparison, along with comparison of pollen measurements and data on health impacts, will help test its accuracy.

"We will also use hindcasting of historic suspected asthma storms to see what our new system shows us. Once we understand its performance, we will have much more confidence forecasting.

"We think we can enhance the current system, and many from the international community are looking to see what we deliver.”

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