Evaporation in Tropical & Humid Climates
High heat but high humidity changes the evaporation picture in the tropics — and makes algae and water quality as important as water loss.
The tropics flip the usual intuition: it is hot, but it is also humid, and humidity suppresses evaporation. Because the rate is driven by the vapour-pressure deficit — not temperature alone — humid tropical air, already near saturation, pulls moisture off the surface more slowly than dry desert air at the same temperature. Annual loss is real but humidity-limited (often 1,200–1,800 mm), and warming is increasing it for small storages (Aminzadeh et al., 2024).
What works best here
In the tropics, the case for covering is often as much about water quality as water loss. Year-round warmth and sunlight drive algae, so light-blocking modular floating covers, geomembrane covers and suspended covers deliver a large algae-control benefit on top of evaporation savings — see how covers help with algae. Low-cost biological options such as duckweed can suit small, sheltered ponds, though they carry oxygen and ecology trade-offs.
What to watch
Heavy seasonal rainfall is the catch: covers must shed or pass rainwater, and chemical monolayers are quickly disrupted by rain, so they are a poor fit. Because radiation is high, the energy-budget method is a sound way to estimate loss where humidity makes simple deficit-based estimates uncertain.