Table 2. Summary of environmental variables used in the analysis of highly pathogenic avian influenza (HPAI) H5N1 occurrences in wild birds in Europe.

Category Description of variables Abbreviation Unit
Anthropogenic environmental variables Distance to the nearest city City km
Distance to the nearest metropolis Metro km
Distance to the nearest road Road km
Distance to the nearest highway Highway km
Distance to the nearest railway Railway km
Human population density in 2005 Hpopden p/km2
Poultry density in 2005 Poultryden p/km2

Physical
environmental variables

Distance to the nearest lake or wetland GLWD km
Distance to the nearest Ramsar site Ramsar km
Digital elevation model DEM m
Slope aspect Aspect °
Slope gradient Slope °
Mean annual potential evapotranspiration Mapet mm/km2/year
Mean annual aridity index Maaridity No unit
Mean monthly precipitation PrecJan to Dec mm
Mean monthly minimum temperature TminJan toDec °Cæ*10
Mean monthly maximum temperature TmaxJan to Dec °Cæ*10
Monthly NDVI NDVIJan to Dec No unit
Interaction variables Poultry density * distance to the lake or wetland PoultrydenW No unit
Poultry density * distance to the Ramsar site PoultrydenR No unit