Combining dispersion modelling with synoptic patterns to understand the wind-borne transport into the UK of the bluetongue disease vector

Bluetongue, an economically important animal disease, can be spread over long distances by carriage of insect vectors (Culicoides biting midges) on the wind. The weather conditions which influence the midge’s flight are controlled by synoptic scale atmospheric circulations. A method is proposed that links wind-borne dispersion of the insects to synoptic circulation through the use of a dispersion model in combination with principal component analysis (PCA) and cluster analysis. We illustrate how to identify the main synoptic situations present during times of midge incursions into the UK from the European continent. A PCA was conducted on high-pass-filtered mean sea-level pressure data for a domain centred over north-west Europe from 2005 to 2007. A clustering algorithm applied to the PCA scores indicated the data should be divided into five classes for which averages were calculated, providing a classification of the main synoptic types present. Midge incursion events were found to mainly occur in two synoptic categories; 64.8% were associated with a pattern displaying a pressure gradient over the North Atlantic leading to moderate south-westerly flow over the UK and 17.9% of the events occurred when high pressure dominated the region leading to south-easterly or easterly winds. The winds indicated by the pressure maps generally compared well against observations from a surface station and analysis charts. This technique could be used to assess frequency and timings of incursions of virus into new areas on seasonal and decadal timescales, currently not possible with other dispersion or biological modelling methods

The use of numerical flow and transport models in environmental analyses

This chapter provides an overview of alternative approaches for modeling water flow and contaminant transport problems in soils and groundwater. Special focus is on flow and transport processes in the variably saturated vadose zone between the soil surface and the groundwater table. The governing flow and transport equations are discussed for both equilibrium and nonequilibrium flow conditions, followed by three examples. The first example shows how one-dimensional root-zone modeling can be used to estimate short- and long-term recharge rates, including contaminant transport through the vadose zone. A second example illustrates a two-dimensional application involving drip irrigation, while the third example deals with two-dimensional nonequilibrium transport of a pesticide in a tile-drained field soil. Also discussed are alternative pore-scale modeling approaches that may provide a better understanding of the basic physical and geochemical processes affecting fluid flow and contaminant transport in saturated and variably saturated media