Dew

Dew is the phenomenon of liquid water droplets forming on surfaces when water vapor in the air condenses as the surface cools below the dew point. It typically occurs during clear, calm nights when surfaces radiate heat to the sky and cool more quickly than the surrounding air. If surface temperatures drop below freezing, frost may form instead of dew.

Formation depends on several conditions: high relative humidity, sufficient cooling of the surface, and light or no wind to reduce mixing and keep the surface near its temperature. The dew point is the temperature at which the air becomes saturated with water vapor; when the surface temperature falls to or below this point, condensation begins and droplets accumulate on leaves, grass, rocks, vehicles, and other exposed surfaces.

Dew is distinct from fog and frost. Fog consists of suspended droplets in the air, not on surfaces. Frost forms when the surface temperature falls below 0°C and water vapor deposits as ice rather than liquid. Dew often dries after sunrise as temperatures rise, but it can persist longer on shaded or protected surfaces.

Ecological and practical aspects vary. Dew can provide a small source of moisture for plants and soil, especially in arid or Mediterranean climates, and can influence leaf wetness and disease risk. Humans have explored dew harvesting in some regions, using nets or collectors to capture and use condensate as a supplementary water source. Overall, dew is a common meteorological phenomenon driven by radiative cooling and atmospheric humidity.