Evaporação em superfície de água livre com baixa turbidez

Abstract

This work aimed to quantify the evaporation on free water surface with low turbidity by three different methods (mass balance, energy balance with Bowen Ratio and mass transfer) under tropical conditions. In addition, comparisons were made between the three methods of determining water evaporation, as well as analyzes of the components of the radiation balance and the albedo. The experimental area is located at Fazenda Santo Antônio, owned by DANCO Comércio e Indústria de Fumos Ltda., In the municipality of Governador Mangabeira, Bahia (12o37 'S, 39o03' W, 218 m). Currently, there are nineteen reservoirs on the farm, of which thirteen are used for storage of low turbidity water for irrigation of tobacco (Sumatripanus tabacum L.) tobacco of Sumatra type for cigar cover. For this purpose, data were collected on two floating platforms installed in waterproof blanket lined reservoirs that store water with low turbidity and a meteorological tower in the experimental area during different periods of the years 2015 and 2016. The total evaporation slides were Indicating that the results were reliable and the appropriate methods in the estimation of evaporation. Being the largest blade for the mass transfer method (424 mm), followed by mass balance (353 mm) and energy balance with Bowen Ratio (350 mm). Daily evaporation according to the mass transfer method ranged from 2.4 to 9.4 mm, with an average of 5.7 mm dia-1. With the mass balance method, a variation of 0.7 to 8.2 mm of evaporation with a mean of 4.8 mm dia-1 was observed. In the Bowen ratio energy balance method, the evaporation ranged from 0.61 to 8.0 mm, with an average of 4.7 mm dia-1. The daily evaporation obtained was relatively low for the three methods, since the water is of low turdidity and there is no impediment to propagation of the solar radiation to great depths. The attenuation of the cloudiness on the incident solar radiation impacted the component of the reflected radiation whose average value decreased from 13 W m-2 to 5 W m-2 with increased cloud cover. The shortwave balance, consequently, also reduced with the cloudiness, with variation of -71%. The long wave emission by both the atmosphere and the surface of the water are the components of the radiation balance of smaller variation in the period of 24 hours. The albedo of water with low turbidity reaches values as low as 2% under clear sky, being strongly influenced by atmospheric cloudiness and elevation angle of the sun. With high cloud cover (low atmospheric transmissivity), the albedo's dependence on water and rising sunshine is not as clear as that under clear sky conditions.