Wet roof cooling is most effective under what weather conditions?

Wet roof cooling is most effective in conditions of low humidity and high temperature. Under these conditions, the primary mechanism at work is evaporative cooling. When the roof surface is wet, the heat from the surrounding air causes the water to evaporate. This process absorbs a significant amount of heat, effectively cooling the roof surface and, consequently, the interior space of the building.

High temperatures provide a strong driving force for evaporation, as warmer air can hold more moisture. Meanwhile, low humidity means that the air is less saturated with moisture, allowing more water to evaporate without reaching the point of saturation. This combination maximizes the efficiency of the wet roof cooling system, leading to lower temperatures inside the building.

In contrast, in conditions of high humidity, the air already contains a significant amount of moisture, which limits the rate at which additional water can evaporate. This reduces the potential cooling effect. Therefore, for wet roof cooling to be most effective, the ideal scenario is low humidity alongside high temperatures.