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Evaporation and evapo-transpiration
Published in Amithirigala Widhanelage Jayawardena, Fluid Mechanics, Hydraulics, Hydrology and Water Resources for Civil Engineers, 2021
Amithirigala Widhanelage Jayawardena
The rate of evaporation is strongly affected by vapour pressure deficit. The rate at which water molecules escape into the air is proportional to ew, and, the rate at which vapour molecules escape into water is proportional to ea, where ew and ea are the vapour pressures of water and air. Therefore, the rate of evaporation is proportional to (ew − ea) which is the vapour pressure deficit.
Effect of micro climatic indices on the accuracy of thermographic plant water status monitoring, case study of a semi-arid area
Published in Quantitative InfraRed Thermography Journal, 2021
Pedram Shoa, Abbas Hemmat, Mahdi Gheysari, Rassoul Amirfattahi
Time of measurements in a day affects canopy temperature and also thermal indices. Since a daily monitoring of plant water status is convincing, the optimal time of measurement should be determined [19]. Researchers proposed to do the measurements at midday in the Mediterranean climate, because higher air temperature and incident solar radiation can increase the atmospheric demand. This could increase the temperature difference between stressed and unstressed plant, hence the accuracy of the method [4,8]. Local climatic conditions can dedicate the best measurement time, since the ‘time’ is a dual aspect problem. First, it changes the canopy temperature due to the changes in amount of incident solar radiation or the changes in the proportion of sunlit to shaded leaves at each part of the canopy. Second, it changes the canopy temperature due to the changes in plant transpiration during a day, due to the microclimate indicator of vapour pressure deficit (VPD). It is so evident that there is no prescription for the best time and direction at all plant specious and climatic conditions, which should be precisely specify.
Climate change and extreme weather: A review focusing on the continental United States
Published in Journal of the Air & Waste Management Association, 2021
The “demand” of the atmosphere for water, and thus the pace of evaporation from the surface, is proportional to the difference between the saturation vapor pressure and the actual vapor pressure of near-surface air, denoted the vapor pressure deficit. Anderson (1936) argued, “The vapor pressure deficit is a much more sensitive indicator of the water vapor conditions of the atmosphere and undergoes greater variations for temperature changes than does the relative humidity.” High values of the vapor pressure deficit are associated with significant outbreaks of wildland fire (Seager et al. 2015a). Moreover, spring and summer values of the vapor pressure deficit have shown significant increases since 1960 in fire-prone regions of the U.S. Southwest. As described above, higher values of the vapor pressure deficit, which are a priori associated with higher temperatures through the Clausius-Clapeyron relation, will tend to amplify this warmth as the surface dries out and evaporative cooling is reduced. Williams et al. (2019) further show that the vapor pressure deficit is strongly associated with the area burned in California fire seasons from 1972 through 2018, and they confirm the rising trend in vapor pressure deficit during this period. Thus, a strong connection is drawn from climate change to extremely hot and dry conditions and to wildland fire, although, as noted below, changes to a landscape also influence the frequency and severity of wildfires.
Estimating the impact of crops on peak loads of a Building-Integrated Agriculture space
Published in Science and Technology for the Built Environment, 2020
Marie-Hélène Talbot, Danielle Monfet
The selected indoor air conditions are based on values proposed in the literature, and a narrow valid range is used to estimate the latent cooling load only. An analysis of the vapor pressure deficit (VPD), the difference between the vapor pressure inside the leaf to the vapor pressure of the air, which is often used by growers to maintain the indoor air conditions instead of controlling the temperature and the humidity independently, is conducted. For lettuce and other leafy greens, it is recommended to maintain the VPD between 0.65 kPa and 0.9 kPa (Kuack 2017), as illustrated in Table 6 by the white cells.