Abstract
Abstract. We develop a prognostic model called Pollen Emissions for Climate Models (PECM) for use within regional and global climate models to simulate pollen counts over the seasonal cycle based on geography, vegetation type, and meteorological parameters. Using modern surface pollen count data, empirical relationships between prior-year annual average temperature and pollen season start dates and end dates are developed for deciduous broadleaf trees (Acer, Alnus, Betula, Fraxinus, Morus, Platanus, Populus, Quercus, Ulmus), evergreen needleleaf trees (Cupressaceae, Pinaceae), grasses (Poaceae; C3, C4), and ragweed (Ambrosia). This regression model explains as much as 57 % of the variance in pollen phenological dates, and it is used to create a climate-flexible phenology that can be used to study the response of wind-driven pollen emissions to climate change. The emissions model is evaluated in the Regional Climate Model version 4 (RegCM4) over the continental United States by prescribing an emission potential from PECM and transporting pollen as aerosol tracers. We evaluate two different pollen emissions scenarios in the model using (1) a taxa-specific land cover database, phenology, and emission potential, and (2) a plant functional type (PFT) land cover, phenology, and emission potential. The simulated surface pollen concentrations for both simulations are evaluated against observed surface pollen counts in five climatic subregions. Given prescribed pollen emissions, the RegCM4 simulates observed concentrations within an order of magnitude, although the performance of the simulations in any subregion is strongly related to the land cover representation and the number of observation sites used to create the empirical phenological relationship. The taxa-based model provides a better representation of the phenology of tree-based pollen counts than the PFT-based model; however, we note that the PFT-based version provides a useful and climate-flexible emissions model for the general representation of the pollen phenology over the United States.
Highlights
Pollen grains are released from plants to transmit the male genetic material for reproduction
After sensitivity experiments of running pollen emissions in Regional Climate Model version 4 (RegCM4), we find that the literature value of pannual for Poaceae provides better agreement with observations for C4 grass when reduced by a factor of 10; we use this value
We have developed a climate-flexible pollen emissions model (PECM) for the 13 most prevalent wind-pollinating taxa in the United States based on observed pollen counts
Summary
Pollen grains are released from plants to transmit the male genetic material for reproduction. Pollen season phenology in an anemophilous species is inherently connected to its environment via relationships in the growing season dynamics (e.g., bud burst and temperature; Fu et al, 2012), and many models apply the same techniques to flowering as for bud burst (Chuine et al, 1999) This approach to phenology could be suited to climate models, given its flexibility for adaptive phenological events and regional-scale studies. Observation-based methods assume stationarity, or the likelihood that the statistics of pollen counts or climate variables are not changing over time For these models to apply outside of calibration period, they require that the driving pattern or relationship is maintained in the future (or past). The limitations of this emissions framework and suggestions for future developments are included (Sect. 6)
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