Observation and simulation of dew in rural and urban environments

Dew has broad relevance to physical geography and many human activities. This paper reviews the observation and simulation of rural and urban dew, and the implications of dew as a climatic phenomenon. There is no universal protocol for measuring dew (i.e., condensation on cooled surfaces), its component fluxes (dewfall and distillation) or guttation, which is 'dewdrops' exuded from leaves. The many methods that exist to measure dew and surface moisture range from simple visual assessment, to electronic wetness sensors, lysimetry and remote sensing. Most studies of dew are rural; urban dew data are rare and studies seldom address dew in patchy landscapes, e. g., a forest clearing. Hardware dew models are rare. Numerous numerical models exist to simulate or forecast dew on rural crops but few address dew for surfaces other than leaves, e. g., a cocoa pod or road. There is a general consensus in the literature that dew is reduced or absent in cities because of the urban heat island effect and reduced vapour supply. However, little data exist to test this. Given the broad relevance of dew to many topics, future studies of dew in complex landscapes, including urban areas, would prove valuable.