Articles | Volume 10, issue 11
Geosci. Model Dev., 10, 4105–4127, 2017
Geosci. Model Dev., 10, 4105–4127, 2017

Development and technical paper 13 Nov 2017

Development and technical paper | 13 Nov 2017

A prognostic pollen emissions model for climate models (PECM1.0)

Matthew C. Wozniak and Allison L. Steiner Matthew C. Wozniak and Allison L. Steiner
  • Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA

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.

Short summary
A new parameterization, Pollen Emissions for Climate Models (PECM), has been developed for use in climate models. New developments include (1) a new climate-sensitive, observation-based phenological model, (2) inclusion of the 13 highest-pollinating taxa in the United States, and (3) an option to compute pollen emissions by plant functional type (PFT). It can be used to address topics like impacts of climate change (e.g., on allergen exposure, on plant ecology) or pollen as an atmospheric aerosol.