Results of mesoscale meteorological model simulations of topography effects on Mountain Pine Beetle (dendroctonus ponderosae) transport and dispersion

The mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreak in the central interior of British Columbia has reached epidemic proportions affecting over 7 million hectares of forest based on trees killed prior to the 2005 flight. The mountain pine beetles emerge from the bark of host pine trees after they have reached biological maturity on days during July or August in which the temperature is between 18 and 30 C, with light winds and no precipitation. Peak emergence occurs over a few days when temperatures are greater than 25 °C (Anhold and Jenkins 1987). Upon emergence, the beetles seek new host trees to colonize and produce larvae, relying on mass-attack to overwhelm the resistance of the pine tree. When MPB fly or are carried above the canopy, they are believed to be advected by the wind much like inert particles. Under the warm and light-wind conditions when MPB are known to fly, terrain-induced thermal circulations are likely to dominate the near-surface wind field. Therefore the nature of the topography and its effect on local wind circulations will affect the dispersal of MPB.

This research project consists of two main parts: validation of the atmospheric models used in the study with an SO2 air pollution dispersion case study and determination of fundamental relationships between topographic effects on atmospheric circulation and MPB dispersal (the basis for this presentation). Two models are employed: RAMS, a mesoscale atmospheric numerical model, is used to produce the 3-dimensional meteorological fields necessary to drive HYPACT, a lagrangian particle dispersion model used to disperse the particles (MPB). The topography of the domain and the model initialization are idealized in order to clarify the effect of topography on local wind circulations. Qualitative analysis of the wind fields produced from simulations with artificial topography will be provided to show the wind pattern in relation to the underlying topography and upper-level meteorological conditions. Quantitative analysis of the resultant meteorological model output will show the relative significance of each of the combinations of initial conditions. Further analysis will show how MPB that are carried above the canopy are carried by the prevailing winds and the resultant MPB spatial distribution.