The plane trees are flowering

The season cometh

pollen Sept 21 2016 b

I had the great privilege of introducing a group of work experience students to the joys of pollen counting the other day.  And what a fun and engaging time we had together, finding out what pollen is, where it comes from, the different types of pollen and how the pollen of some plants can affect our health.

Amazingly they went from the awe and wonderment of seeing a pollen grain with a microscope for the first time, to counting and identifying pollen a couple of hours later.  What a terrific bunch!

Today's picture shows what was in the air on Thursday September 22 and the students tell me the count was 83 pollen grains per cubic metre of air.  We're now well into the tree pollen season and the slide mainly contained pine and plane tree pollen.  There was even one grass pollen grain, the first but sadly not the last of the season.

Officially we'll start counting on October 1 but will spend the next few days checking out the system and making sure it's all working as it should.

The elm movie

The elms are flowering

On Thursday Sept 8 the pollen count was 36 grains per cubic metre of air and we saw something new in the air as well - elm pollen.  Although the elms still lack leaves they are now flowering and their wind-borne pollen is known to cause allergies.  Most of the pollen on Thursday was from pine but about a third was elm.  Our friends at the Canberra pollen count wrote a great little article on elms in Australia which you can read here.

Over the next few weeks we expect to start seeing pollen from several more tree species.

Forecasting the grass pollen season

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Even though the grass pollen season won't start until sometime in late October, we're already predicting it will be a heavier than normal grass pollen season this year.

But how on earth do we know that?

As it happens one of our best indicators of the coming season isn't actually here on Earth at all but above us in space.

Satellites.

Satellites regularly take images of our planet at various wavelengths of light.  Chlorophyll, the green pigment in plant leaves, absorbs light of particular wavelengths and uses this energy to make food from carbon dioxide and water through a process known as photosynthesis.  Measuring how much chlorophyll there is in a plant is a good way of finding out how healthy it is.

Chlorophyll levels can be measured from satellite imagery using the Normalised Difference Vegetation Index or NDVI, a unit-less ratio that ranges between -1.0 and +1.0.  Positive NDVI values are associated with a greater density and greeness of plants and NDVI values close to 0 or below are associated with bare soil, urban areas and bodies of water.

Today's picture, taken from the Bureau of Meteorology website, shows Victoria's average NDVI for August.

You'll see that large areas of the state are looking pretty green coming out of winter, especially those grazing and cropping areas to Melbourne's west and north.  In short the green areas show that a fair chunk of the state's four million hectares of perennial ryegrass pastures, the source of Melbourne's allergenic grass pollen, is in pretty good health and growing well.

That growth is setting us up for one of the best (or worst, depending on your point-of-view) grass pollen seasons in recent years.

But this outlook isn't locked in.  For instance if September rainfall disappoints there will likely be some reduction to the size of the season.

But with decent spring rains we could be in for quite a season.

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