Breathe easier?

Nov. 7, 2014

How has it been going this year?

In an article published a couple of months ago in the Conversation, I forecast a mild grass pollen season for Melbourne this year. So I thought I’d update you on how that prediction’s tracking.

One way of assessing how the season is progressing is by looking at the cumulative total of grass pollen grains. That is, add each daily count to the sum of all the previous daily counts from October 1 – that’s the red line in today’s graph – and compare that line to the cumulative counts of other seasons. The blue line is our average grass season and the two dashed lines are our worst season in 1993, when the cumulative total of grass pollen grains of over 6,700, and our mildest season in 2008, when the total was just over 1,000 grass pollen grains.

To put 'worst' and 'mildest' into some perspective, there are 92 days between October 1 and December 31, which is the period we count. So in 1993 the average grass pollen count was over 70 grains per day. That’s well into the high range and on a high day it is likely that all people sensitive to grass pollen will experience hay fever symptoms. By comparison, in our mildest season yet, 2008, the average daily count was only about 10, which is comfortably in our low range of grass pollen counts.

So what the graph shows is that the current season is tracking 2008 pretty closely with a gap already opening up between this season and an average season. As there’s been little rainfall over much of western Victoria since July, and that’s where most of our grass pollen comes from, I can’t see the current situation changing and expect that the gap will likely continue to widen.

That means we’re on track for one of our mildest seasons yet.

But I’m not saying you won’t suffer some hay fever this year; just it won’t be as bad as previous years. And certainly nowhere near as bad as 1993.



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