For many, spring is the most agreeable time of year. But for one in six people (around three million Australians), this balmiest of seasons is rendered utterly miserable by allergic rhinitis or hay fever. A chronic condition that reduces the quality of life of sufferers in multiple ways, hay fever is also associated with asthma.
For a small handful of Australians, including the two of us, spring also marks the start of the pollen counting season with its daily rituals of collecting slides, counting and identifying pollen, and tallying the results. We are the pollen counters for Melbourne and Canberra. Most other cities in Australia either don’t have pollen counters, or have sporadic ones.
The main problem with pollen counting is that most allergy sufferers don’t care about today’s pollen count; they want tomorrow’s, and the next day and the day after that. It’s the pollen forecast that helps them most.
And, at this time of year, what most people want to know is if this is going to be a bad season with lots of hay fever or a mild season with only the occasional bad day. They’re also curious about why the pollen season changes from year to year – is it because of climate change or something else entirely?
An incomplete picture
First, there isn’t just one pollen season but many; each plant species sheds its pollen at a different time of year.
The wind-borne pollen of certain grasses, particularly pasture grasses such as perennial rye grass, are Australia’s number one cause of hay fever. That’s why pollen counters in Australia focus on the grass pollen season and why we start each season by forecasting its likely intensity.
We all know Australia is a big country, but it’s also a long one stretching all the way from the hotter tropical north to the cooler temperate south. The types of grasses and when they flower all change across that range of latitudes. But the major environmental factors grasses respond to are rainfall and temperature.
The figure above shows how the grass pollen season changes as we move down Australia’s east coast. Even though the Brisbane counts are from the 1990s, Hobart and Canberra counts from the mid-2000s and Melbourne and Sydney counts from the last few years, these are – surprisingly – the best data we have for Australia’s grass pollen seasons.
The green, green grass
In northern Australia, the temperatures are milder and grasses can grow whenever there’s been enough rain. So the grass pollen season in the north is much longer than in the south and is driven by summer rainfall. The types of grasses in northern Australia are also different to those further south and their pollen has different allergens.
Presumably, the intensity of Brisbane’s grass pollen season is tied to the strength of the wet season and the cycle of drier El Ninos and wetter La Ninas.
In southern Australia, grass growth is about rainfall in autumn and spring. In the cool winter months, grasses don’t grow much and only really take off once the warmer spring weather comes along. But once the hot summer kicks in, they turn to straw and wait for the seasonal cycle to repeat.
Well, that’s what we suspect, although for most Australian cities the lack of daily pollen counts across several years limits our ability to forecast seasons and interpret trends. That seems a little odd in a country with rates of hay fever and asthma that are among the highest in the world.
While how much grass is growing is obviously related to the daily pollen count, this is just one of the factors at play. Temperature also has a role. But how temperature relates to grass pollen counts depends on where you live.
Taking in the temperature
Take Melbourne, where the main source of grass pollen is the pastures to its north and west. Pollen comes into the city on north and north-westerly winds that are warmed as they pass over the land. Cooler southerly winds, coming up from Bass Strait, are largely pollen-free.
So Melbourne’s worst hay fever is during November’s warm days.
Canberra, being land-locked and set on a former sheep station, is often considered a hot-spot for grass pollen allergies in Australia. The capital’s worst hay fever days are similar to Melbourne’s as they’re associated with north-westerly winds that bring in grass pollen from pastures round Goulburn, home of the big merino.
But Canberra is also a bush capital and winds from other directions, while still warm, blow over native forests and carry with them less grass pollen. The relationship to temperature is less clear cut. And of course it largely depends on the season – in a mild year, the grasses stop flowering and draw the season to an early close.
The future of hay fever
The two factors that will affect future pollen seasons are doubtless changes in the landscape and climate change. Urban expansion, forest clearance, changes to farming practices and the abundance of exotic weeds will all have consequences for our pollen seasons.
Common ragweed, for example, a native of North America, is an established weed in Europe where its pollen extends the hay fever season into autumn. Ragweed pollen is far more allergenic than grass pollen and could become a real health problem if it ever becomes widespread in Australia.
Climate change is undoubtedly also a concern. The predicted rise in temperatures and changing rainfall patterns have the potential to extend the length of the grass pollen season as well as providing spaces in which new allergenic plants can become established.
Good long-term records of Australia’s pollen seasons will be key to tackling the changing allergy problems that come with spring each year. And we’re on it.
Oh, and for those who are wondering about the forecast for this year’s season, without further spring rainfall we’re expecting Melbourne will experience quite a mild grass pollen season this year. Sadly for Canberra, it’s already looking like another bad season.
While we’d like to forecast the grass pollen season nationally, the lack of a coordinated network means this just isn’t possible right now.