How is humidity related to evaporative cooling?

Evaporative cooling relies on the process of water transitioning from a liquid state to a vapor state, which absorbs heat and cools the surrounding air. Humidity is a measure of the amount of water vapor present in the air. When humidity levels are high, the air is already saturated with moisture, meaning that it cannot absorb much more water vapor. This saturation significantly reduces the rate at which water can evaporate because the air cannot hold additional moisture.

As a result, in conditions of high humidity, the effectiveness of evaporative cooling is diminished. This is why high humidity is associated with a reduction in the cooling effect from evaporation; people often feel hot and uncomfortable in humid conditions because sweat does not evaporate efficiently from the skin, inhibiting the body’s natural cooling mechanism. In contrast, lower humidity allows for more effective evaporative cooling, as the air can accommodate more evaporated moisture, leading to a greater cooling effect.