The start dates of birch pollen seasons in Fennoscandia studied by NOAA AVHRR NDVI data

A change in climate in northern Europe in the last decades has probably changed the timing of onset of the birch pollen season. In Denmark it is reported that from 1977 to 2000 the date on which the accumulated birch pollen counts reached 2.5 percent of the total catch has changed from 12th of May to 25th of April. The total cumulated amount of birch pollen has also increased 2-3 times. The Global Inventory Monitoring and Modeling System (GIMMS) Normalized Difference Vegetation Index (NDVI) dataset from 1982 to 1999 was used to investigate whether low resolution satellite data can be used for measuring the budburst of birch, that coincide well with the start of the birch pollen season. This study indicates that NDVI values computed from low resolution low data-cost satellites can be used to monitor the start date of birch pollen In the spring, even in areas where the birch is not the dominating tree species. This can be used to improve forecast models for pollen and look for evidence of climatic change. It was found that during the 18 years period studied, the start date of the birch pollen season is stable or delayed in northern Fennoscandia and high latitude areas. In southern Fennoscandia and oceanic parts of western Norway the onset of the birch pollen season is considerable earlier.