Articles | Volume 13, issue 9
Research article
11 May 2016
Research article |  | 11 May 2016

Ragweed pollen production and dispersion modelling within a regional climate system, calibration and application over Europe

Li Liu, Fabien Solmon, Robert Vautard, Lynda Hamaoui-Laguel, Csaba Zsolt Torma, and Filippo Giorgi

Abstract. Common ragweed (Ambrosia artemisiifolia L.) is a highly allergenic and invasive plant in Europe. Its pollen can be transported over large distances and has been recognized as a significant cause of hay fever and asthma (D'Amato et al., 2007; Burbach et al., 2009). To simulate production and dispersion of common ragweed pollen, we implement a pollen emission and transport module in the Regional Climate Model (RegCM) version 4 using the framework of the Community Land Model (CLM) version 4.5. In this online approach pollen emissions are calculated based on the modelling of plant distribution, pollen production, species-specific phenology, flowering probability, and flux response to meteorological conditions. A pollen tracer model is used to describe pollen advective transport, turbulent mixing, dry and wet deposition.

The model is then applied and evaluated on a European domain for the period 2000–2010. To reduce the large uncertainties notably due to the lack of information on ragweed density distribution, a calibration based on airborne pollen observations is used. Accordingly a cross validation is conducted and shows reasonable error and sensitivity of the calibration. Resulting simulations show that the model captures the gross features of the pollen concentrations found in Europe, and reproduce reasonably both the spatial and temporal patterns of flowering season and associated pollen concentrations measured over Europe. The model can explain 68.6, 39.2, and 34.3 % of the observed variance in starting, central, and ending dates of the pollen season with associated root mean square error (RMSE) equal to 4.7, 3.9, and 7.0 days, respectively. The correlation between simulated and observed daily concentrations time series reaches 0.69. Statistical scores show that the model performs better over the central Europe source region where pollen loads are larger and the model is better constrained.

From these simulations health risks associated to common ragweed pollen spread are evaluated through calculation of exposure time above health-relevant threshold levels. The total risk area with concentration above 5 grains m−3 takes up 29.5 % of domain. The longest exposure time occurs on Pannonian Plain, where the number of days per year with the daily concentration above 20 grains m−3 exceeds 30.

Short summary
To study the distribution of airborne ragweed pollen in changing environments and associated health risks over Europe, we introduce an approach with explicit treatment of pollen ripening, release and dispersion due to environmental drivers in an online modelling framework where climate is integrated with dispersion and vegetation production. From a simulated pollen season and concentration pattern health risks are evaluated through calculation of exposure time above health-relevant threshold levels.
Final-revised paper