Simulated Pollen Dispersion in an Island Environment.

Complex terrain can create small-scale circulations which substantially affect pollen dispersion but might not be detected by meteorological networks and coarse-grid meteorological models.  These circulations are present on volcanic islands as a result of differential heating between land and sea as well as their rugged terrain. To improve understanding of pollen dispersion in this environment, we simulated the transport of three pollen types from agricultural regions of the Hawaiian island Kauai for 12 days between 2005 and 2008.  The dates were chosen to span a range of climatological conditions including La Niña, El Niño, and neutral conditions according to the Oceanic Niño Index.  Meteorological conditions were simulated with the Weather Research and Forecasting Version 3.1 model using a horizontal resolution of 500 m in the innermost domain to capture small-scale circulations.  Predicted wind conditions were in close agreement with surface and upper-air measurements taken at Lihue, HI. Both pollen size and source location had major effects on dispersion over and near the island. As expected, smaller pollen grains traveled farther than larger grains before settling due to their slower terminal fall speed.  Where transport was directed inland, pollen grains were funneled through valleys rather than upslope.  When transport was directed over the ocean, simulated deposition was greatest near the source with dispersive tails following the mean wind.  Some pollen grains were transported to the island of Ni’hau 35 km away.  These results are the first to predict the interactions between complex island terrain, local climatology, and pollen dispersion.