The Cause & Effects of Morning Dew

Condensation

• Condensation begins when water is evaporated into the air during the daytime heat, when the sun beats down on liquid water. The water molecules with the highest energy will vaporize into the air. Later, once the sun goes down and the air with all this water cools, solid objects will cool faster since they have a lower specific heat than the moist air. When there is not enough heat to keep the vaporized water in a gaseous state, it will condense into liquid water on the coolest surfaces in small droplets.

Seasons

• Dew can occur during every season and in any climate, though in the winter months the ambient temperature is often below the freezing point of water, causing the dew to freeze. This is known as frost. Frost can be damaging to plants, as frost expands within plant cells and breaks their cell walls. One notable difference between dew and frost is that on a car windshield, frost will form on the inside of the glass, while dew forms on the outside of the glass. This is because the glass conducts heat well, and will cool the air adjacent to the inside of the glass until water vapor condenses.

Uses

• While frost can be damaging to crops, especially to crops like apples that have delicate buds in the early springtime, dew is essential to ecosystems. Desert plants especially rely on dew as their only source of hydration. The cactus evolved to minimize its loss of water to evaporation by developing tiny spines to reduce the rate of transpiration. People can survive in the desert by collecting dew using a plastic sheet stretched out near the ground, where what little moisture is in the air will condense in the early morning hours.

Conditions

• Dew and frost do not occur every night, nor do they form on every surface. If the air does not become saturated with moisture, then dew and frost will not form. Dew only forms when the temperature reaches a special temperature called the dew point, which is the temperature at which saturation occurs. There are many short lyrics that have been used to predict when dew will form, along with the weather that follows dew, including one that claims rain will fall on days without dew, and clear skies will follow mornings with dew. Dew tends to form on plants close to the ground since the air is colder around them, while taller plants do not tend to become covered in dew since the air surrounding them is warmer.