1National Center for Atmospheric Research, Atmospheric Chemistry Division, Boulder, CO, USA
2Labortatory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman, WA, USA
3University of Southern California, Los Angeles, CA, USA
4Department of Chemical Engineering, California Institute of Technology, Pasadena, CA, USA
5National Center for Atmospheric Research, Research Applications Laboratory, Boulder, CO, USA
6Climate Science and Policy, Science and Technology Program, University of Washington, Bothell, WA, USA
Abstract. A pollen model that simulates the timing and production of wind-dispersed allergenic pollen by terrestrial, temperate vegetation has been developed to quantify how pollen occurrence may be affected by climate change and to investigate how pollen can interact with anthropogenic pollutants to affect human health. The Simulator of the Timing and Magnitude of Pollen Season (STaMPS) model is driven by local meteorological conditions and is designed to be sensitive to climate shifts, as well as flexible with respect to the vegetation species and plant functional types (trees, grasses, etc.) represented and the climate zones simulated. The initial focus for the model is the simulation of the pollen emission potential of important allergenic tree and grass species that typically flower between March–June in Southern California (S. CA), which is characterized by moderate Mediterranean and oceanic climate zones as well as regions of arid desert and arid steppe. Vegetation cover and species composition data are obtained from numerous datasets and a database of allergenic vegetation species, their pollen production potential and relative allergenicities has been developed. For the selected allergenic species and spring-early summer simulation period, temperature is the main driver controlling the timing of pollen release, while precipitation (and temperature, for some species) controls the magnitude of pollen produced. The model provides species-specific pollen potential maps for each day of the simulation period; these are then used by a pollen transport model to simulate ambient pollen concentrations as described in a companion paper (Zhang et al., 2013a), which also presents model evaluation results for the S. CA model domain. The STaMPS model was also used to quantify the possible impact of climate change on pollen season under the IPCC SRES A1B scenario as simulated by the ECHAM5 global climate model. Current (1995–2004) and future (2045–2054) meteorological conditions downscaled using the Weather Research and Forecasting (WRF) model were used to drive STaMPS and generate estimates of the relative magnitude and timing of pollen season for important allergenic tree and grass species that bloom from March through June in a larger domain that covers all of CA and Nevada. Differences in the simulated timing and magnitude of pollen season for the selected allergenic species under current and future climate scenarios are presented. The results suggest that across all of the simulated species, pollen season starts an average of 5–6 days earlier under predicted future climatic conditions with an associated average annual domain-wide temperature increase of about 1°C compared to simulated current conditions. Differences in the amount of pollen produced under the two scenarios vary by species and are affected by the selected simulation period (1 March–30 June). Uncertainties associated with the STaMPS model and future model development plans are also discussed.