Grassland Phenology and Meteorology Co-Influence Grass Pollen Counts in Victoria, Australia

Abstract

AIMThis study investigated the role of grassland phenology in driving daily and seasonal pollen counts in Melbourne, Victoria and characterized the ecological conditions leading up to Melbourne’s epidemic thunderstorm asthma event on 21/11/2016. Landscape ecological conditions have traditionally been overlooked as an environmental driver of pollen variability. An understanding of relationships of pollen counts with vegetation type and phenology is valuable to develop better tools to forecast the pollen season and the associated allergenic risks.METHODWe combined 2000-2016 Enhanced Vegetation Index (EVI) data from the Moderate Resolution Imaging Spectroradiometer (MODIS), gridded meteorology products and 1991-2016 grass pollen counts to assess spatial and temporal correspondences among phenology, meteorology and pollen counts in Victoria. Grassland and pollen phenological metrics were analysed for trends and anomalies, and comparisons made of correlations between pollen season metrics and meteorological variables and between pollen season metrics and phenology metrics.RESULTSSeasonal grass pollen highly correlated with the integrated EVI while daily grass pollen highly correlated with meteorology. We detected a broad hotspot area northwest of Melbourne which experienced both anomalously high EVI values and a significant delay of peak EVI date in 2016. > 20% of the landscape had not reached peak EVI by the start of the pollen season (05/10/2016), heightening exposure to local flowering and hence pollen emission.CONCLUSIONWe showed that grass phenology directly controls pollen production, including pollen hotspots, whereas meteorology determines where and when high pollen deposition will occur. Future forecasting of pollen season and the associated allergenic risks should take into account the timing and spatial variability of grassland phenology as well as the co-influences over pollen production, transport and deposition between vegetation and meteorology.