Dec. 1, 2021
The 2021 tree and grass pollen season has been one of the longest and strongest on record. Here we provide a summary of the pollen that really got up your nose this year and what we might expect in the coming weeks.
The 2021 winter to spring pollen season has been extraordinary on a number of fronts. Earlier this year we forecast that pollen production was likely to be higher than average on the basis of a wet winter and high soil moisture as we approached the winter tree pollen season - a similar prediction was put forward for the spring grass pollen season as well.
Little did we know that it would be one of the worst seasons on record for a range of allergenic tree pollen through the mid winter to early spring months, and that this would quickly move into a record grass pollen season in October-November.
A summary of the daily pollen counts for the main allergenic tree pollen taxa and grass pollen for July to November 2021 is illustrated in Figure 1. The graph shows a cascade of tree pollen through the winter months extending into the month of October presenting Canberrans with a persistent and at times EXTREME airborne pollen load, all with the potential of really getting up people's noses.
Figure 1. Selected tree and grass pollen taxa seasons for July to November 2021. The pollen amounts are expressed as stacked daily concentrations (grains/m3) and are colour coded to plant type. The horizontal bars represent the pollen season length for each plant type recorded in 2021.
The beginning of the grass pollen season initially showed signs of being slow to start - but by mid October we witnessed a dramatic rise to unprecedented daily concentrations of airborne grass pollen. We saw not only the record daily grass pollen count (510 grains/m3 on 17th November, 2021), but also the most number of EXTREME grass pollen days in a Spring season - 16 EXTREME days (Figure 2).
Figure 2. Comparison of the daily grass pollen counts for Spring 2020 (Sept-Nov) and 2021 (Sept-Nov) in Canberra (December counts are also displayed for 2020). The histogram shows daily counts colour coded to match the accepted pollen levels reported by CanberraPollen.com.au. The number of extreme, high, moderate and low days for the spring months are also displayed.
A comparison between the daily grass pollen counts for the 2020 and 2021 spring season (Figure 2 and 3) shows the longer and stronger nature of this years grass season - one that is showing no signs of declining as yet. In 2020 the grass pollen season was showing a steady decline in the daily count towards the end of November. This year the grass pollen season still has plenty of "fuel in the tank" with recent rains and warming weather maintaining the green and highly productive grasses in and around Canberra.
Figure 3. Cumulative grass pollen count from 1st October through to 31st December for the period 2007-2009 and 2014-2021. The data summarizes the grass pollen count from the lowest record season (2017) to the highest record season in 2020. The average cumulative pollen count is shown as the black dashed line (including counts from 2007-2009 and 2014-2020). The cumulative grass pollen count for 2021 up until 30th November 2021 is shown by the red line with an unknown trajectory for the month of December indicated by the dotted red line.
If you suffer from hay fever or asthma and you are looking for the light at the end of the tunnel we're afraid it may be some way off. The grass pollen curve is updated in Figure 3 to include the cumulative load of grass pollen for the 2021 season through to the end of November. This shows the unrelenting rise of grass pollen continues with punctuated plateaus caused by periodic heavy rain days, which have been a feature of this record rainfall month of November. The declaration of a La Nina for the spring and coming summer heralds even more rain over the next couple of months at least - driving further growth in grasses and potentially prolonging the grass pollen season into late December and even beyond.
We’ll continue to keep you updated on the progress of this extraordinary pollen season through the @CanberraPollen twitter handle and through the Canberra Pollen app and website. Be sure to check out the AirRater app and website for a geospatial perspective of the pollen and smoke data.