Controversy over transgenic or "genetically modified" (GM) crops has led to increased interest in evaluating and controlling pollen dispersion. In response to this problem we have developed a Lagrangian model of pollen dispersion. The model has been tested by comparison to field measurements of pollen deposition. Predicted surface pollen burden compares favorably both to observations and to results from a standard gaussian plume model.

The Lagrangian technique allows each element of the material being dispersed to be "tagged" according to its source, release time, and other properties. This capability allows pollen viability to be estimated as a function of such factors as travel time, temperature, and relative humidity. We take advantage of this capability in order to evaluate the influence of extreme climate conditions on pollen viability. Results suggest that unusually cool and moist conditions around the time of silking (as may occur in the central U.S. during the warm phase of ENSO events) strongly increase the duration of pollen viability, thereby increasing the likelihood of outcrosses between GM and non-GM varieties.