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Evaporation and Transpiration
Published in Richard J. Chorley, Introduction to Physical Hydrology, 2019
Moisture transfer from a vegetated surface is often referred to as evapotranspiration,1 and when the moisture supply in the soil is unlimited the term potential evapotranspiration (PE) is used. It has been suggested that PE can be defined more specifically as the evaporation equivalent of the available net radiation, i.e. PE = Rn/L, where L is the latent heat of vaporization (59 cal cm-2 ≈ 1 mm evaporation). In some cases this equivalence may be invalid. For example, if an irrigated area is surrounded by dry fields evaporation rates can exceed Rn/L by 25–30%. Air heated by passing over the dry areas upwind maintains the high rates through the downward transfer of sensible heat to the irrigated section-the so-called ‘oasis effect’. Horizontal transport (advection) of sensible heat through the vegetation cover (fig. 4.1.1) can also cause anomalous evaporation rates – termed the ‘clothesline effect’. This occurs when a study plot is not surrounded by a zone with identical vegetation cover and environmental conditions. The ‘buffer zone’ necessary to eliminate these effects varies in size, but may exceed 300 m radius. Neverthless, for all short crops of approximately the same colour and completely covering the ground the PE rate is essentially determined by the total available energy as long as there is unlimited soil water. Plant physiology is important in the case of specialized crops, such as rice and sugar cane (high water use rates) and pineapple (low usage).
A Constructed Wetland System for Treatment of Landfill Leachate, Monroe County, New York
Published in George Mulamoottil, Edward A. McBean, Frank Rovers, Constructed Wetlands for the Treatment of Landfill Leachates, 2018
David A.V. Eckhardt, Jan M. Surface, John H. Peverly
The monthly mean ET measured in this study (90 mm/month) is comparable to pan-evaporation rates for this region (Brutsaert, 1974). Despite the above-average rainfall, ET caused an 8% decrease in outflow relative to inflow. High rates of ET during two summer sample collection periods coincided with dry weather, and the SSF outflow volumes (and the chemical loads) were zero. The high ET rates were due in part to (1) a constant supply of available water, (2) relatively high leachate temperatures, nearly 23°C, in the SF beds during the summer, and (3) interception of rainfall and uptake by the reeds, especially in the SSF beds, where the reeds grew to a density of about 250 plants/m and a height of nearly 3 m. The high rate of ET also is attributed to an oasis effect (Brutsaert, 1982), where evaporation is enhanced when a wet area is surrounded by a dry soil area.
Experimental and Theoretical analysis of the urban overheating and its mitigation potential in a hot arid city – Alice Springs
Published in Architectural Science Review, 2020
Shamila Haddad, Giulia Ulpiani, Riccardo Paolini, Afroditi Synnefa, Mattheos Santamouris
Previous studies in hot-desert cities show a typical climatic pattern, where the urban area is on average cooler than suburban areas during the daytime, producing an Urban Cool Island (UCI), and warmer at night (Lazzarini et al. 2015; Lazzarini, Marpu, and Ghedira 2013). For instance, Bencheikh and Rchid (2012) reported a magnitude of the UCI of − 4.5 °C in the hot desert climate of Ghardaia, Algeria. The diurnal UCI is frequently associated with the irrigation of vegetation resulting in increased evaporative cooling in the urban areas, thus producing an oasis effect, which contrasts with surrounding bare soil environments with limited soil moisture (Georgescu et al. 2011; Lazzarini et al. 2015; Oke 1987). Then, the magnitude of the oasis effect is determined by synoptic conditions, time of day and type of vegetation (Potchter et al. 2008).
Effects of graywater on the growth and survival of ornamental plants in nature-based systems
Published in Journal of Environmental Science and Health, Part A, 2019
Leticia Z. S. Caputo, Camila S. Siqueira, Bruno A. Caputo, Claudia G. V. Bacchi, Fernando J. C. Magalhães Filho, Paula L. Paulo
Canna lily irrigated with GWL presented up to 30% higher ET values than giant horsetail. The evapotranspiration of mesocosms was affected, mainly in the first period, by the “oasis effect.” The oasis effect occurs when small scale wetlands respond to the surrounding microclimate.[26] Such an effect was noted during the first period (Table 4) in the control mesocosms, without plants, where the ET (evaporation) was 45.0% higher than the ET0. Pedescoll et al.[26] compared their results with a full scale constructed wetlands and noticed that ET was four times higher in the mesocosms.
Green infrastructure performance in arid and semi-arid urban environments
Published in Urban Water Journal, 2021
Sara Meerow, Mukunth Natarajan, David Krantz
The identified studies all confirm the oasis effect – that vegetation reduced temperatures in the surrounding area – especially from larger shade trees. Shade trees perform particularly well vis-à-vis other vegetation like grass as an urban heat mitigation strategy when water use is taken into account. For arid environments, where water is limited, there may be a real tradeoff between vegetation benefits and irrigation requirements (Shashua-Bar, Pearlmutter, and Erell 2011).