Vapor plumes in a tropical wet forest: spotting the invisible evaporation

Abstract. Forest evaporation exports a vast amount of water vapor from land ecosystems into the atmosphere. Meanwhile, evaporation during rain events is neglected or considered of minor importance in dense ecosystems. Air convection moves the water vapor upwards leading the formation of large invisible vapor plumes, while the identification of visible vapor plumes has not been studied yet. This work describes the formation process of vapor plumes in a tropical wet forest as evidence of evaporation processes happening during rain events. In the dry season of 2018 at La Selva Biological Station (LSBS) in Costa Rica it was possible to spot visible vapor plumes within the forest canopy. The combination of time-lapse videos at the canopy top with meteorological measurements along the canopy profile allowed to identify the conditions required for this process to happen. This phenomenon happened only during rain events, where evaporation measurements showed contributions of 1.8 mm d⁻¹. Visible vapor plumes during day time occurred on the presence of precipitation (P), air convection identified by the temperature gradient (Δϴ_v / Δz) at 2 m height, and a lifting condensation level at 43 m height (Z_lcl.43) smaller than 100 m.