What factor limits the effectiveness of evaporative cooling in tropical climates?

• A. Wind speed
• B. Air pressure
• C. Humidity
• D. Sun angle

Answer: (C)

Humidity is the factor that limits evaporative cooling in tropical climates because evaporation works best when the surrounding air can still take in more water vapor. If the air is dry, water from a surface can freely evaporate, and that evaporation draws heat away, producing a strong cooling effect. In tropical, highly humid environments, the air is already close to saturation, so it can’t absorb much more water vapor. The driving force for evaporation—the difference between the water’s vapor pressure at the surface and the air’s actual vapor pressure—shrinks, so evaporation slows and less latent heat is removed. While wind can help by moving away the evaporated vapor and modestly improving cooling, it can’t overcome the fundamental limit set by high humidity. Sun angle or air pressure aren’t the primary constraints in this context.