Parts of NZ could be heading into a wetter summer – a blessing in disguise for allergy sufferers

The latest projections suggest New Zealand could be heading into a neutral or La Niña summer, which would bring rainier conditions to the north and east of the country.

While the prospect of a wet summer might not appeal to most people, for pollen allergy sufferers this could be a blessing in disguise.

Our latest research on pollen levels in Auckland backs up what we have long suspected but haven’t had the data to prove.

Unlike many developed countries, New Zealand doesn’t routinely monitor airborne pollen, and speculation about how La Niña and El Niño summers affect allergy sufferers has been just that. Until now.

With new data, we are able to show the El Niño Southern Oscillation (ENSO), which brings us changing phases of a natural climate cycle, can have profound effects on pollen allergy levels in Auckland.

For the one-in-five of us who suffer from hay fever or asthma, this has important implications.

Tracking pollen levels

Over the 2023/24 summer – a dry El Niño season – we monitored pollen levels in Auckland each day using equipment located on top of the War Memorial Museum. This was something of a milestone, marking the first time pollen levels have been monitored in the city this century.

We were able to compare our data with results from two previous pollen monitoring projects conducted almost four decades ago. By a stroke of luck, one of these projects monitored pollen levels during a strong La Niña season in 1988/89 and the second during a neutral summer (neither La Niña nor El Niño).

This comparison clearly showed the pollen season during the La Niña summer was much shorter and less severe than during the other two seasons – just as we would have predicted.

The main reason for the differences was rainfall, which is typically higher and more frequent in northern New Zealand during La Niña summers. Grasses, like all plants, need rainfall to survive and grow but they tend not to release pollen on rainy days which can also ‘flush’ already airborne pollen out of the atmosphere.

So, periods of excessive or sustained rainfall in spring and summer can lead to suppressed or shortened pollen seasons. This seems to have been the case in Auckland during the La Niña summer of 1988/89. The grass pollen season in that year lasted 41 days.

In contrast, the other two seasons had comparatively moderate rainfall – enough to maintain grass growth and pollen production but with plenty of dry, sunny and windy days for higher levels of pollen to be released and spread.

In the 2023/24 El Niño summer, the grass pollen season lasted 77 days, almost twice as long as that seen in 1988/89.

We must acknowledge that a sample of just three seasons bookending a 35-year interval would not normally be a convincing basis for confident conclusions.

Nevertheless, the consistent pattern observed in this limited dataset is in line with expectations about how contrasting weather patterns affect pollen production and dispersal, and the results shouldn’t be sneezed at.

Advice for allergy sufferers

What does this research mean for those of us who suffer from pollen allergies?

Better understanding of pollen season variability and its causes can inform the two pillars of allergy management: treatment and avoidance of allergy triggers.

Sophisticated predictive models can forecast changing La Niña and El Niño phases many months in advance. Now that we can show these phases affect pollen levels, we can be forewarned about the likely severity of the pollen season ahead.

Above all, our research shows that pollen seasons can be highly variable – from one year to the next and likely between regions due to variations in La Niña and El Niño effects in different parts of the country.

This highlights the importance of continuing pollen monitoring to better understand the causes and consequences of seasonal pollen allergy.

Climate change, and in particular rising temperature and atmospheric carbon dioxide levels, altered patterns of precipitation and greater inter-annual variability all likely have an impact on pollen levels in New Zealand.

In the longer term, climate projections suggest Auckland will see increasingly drier and warmer springs and summers – and that’s likely to mean more pollen in the air and more bad news for those with allergies.