Modelización con CFD del efecto de las condiciones de emplazamiento y manejo en las medidas del evaporímetro Clase-A

Abstract

Class-A tanks are widely used to derive open-water evaporation and evapotranspiration. The World Meteorology Organization (WMO) recommends the use of these standard evaporimeters. The impact of pan maintenance conditions and location has been analyzed in this study. A CFD-based (Computational Fluid Dynamics, CFD) methodology have been used to derive convective masstransfer coefficients (wind functions) which are required for estimating evaporation of water bodies with the mass-transfer method. The CFD-derived wind functions have been reported to provide good estimates of hourly and daily evaporation measurements in previous works of the authors. Several factors affecting the rate of pan evaporation have been considered: (1) variation in water level, (2) tank surroundings (bare soil, presence of vegetation) and (3) presence of bird nets. A remarkable sensitivity of tank evaporation to maintenance conditions and location has been observed. Up to 10% variation can be caused by the presence of bird nets and substantial differences are found when the water level decreases below the standard recommended level. The results of the study highlight that tank evaporation data should be used with caution for agronomical and environmental purposes, especially when maintenance is poor.