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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).
Introduction to water ethics
Published in David Groenfeldt, Water Ethics, 2019
The intellectual ancestry of this book includes Aldo Leopold, his son Luna Leopold, and, though too young to qualify as an ancestor, Sandra Postel. Aldo Leopold’s characterization of a land ethic (Leopold 1949) was applied to rivers by his hydrologist son, Luna (Leopold 1977). Sandra Postel breathed new life into the relevance of ethics to water with her book Last Oasis: Facing Water Scarcity (Postel 1997). The common message of these writers is that ethics about protecting and respecting water ecosystems have very real practical ramifications. This is good news, because it suggests that the current unsustainable patterns of water behavior and policies could be reformed by changing the ethics that promote those behaviors. If the water crisis is caused by behaviors, which in turn are driven by ethics, then let’s find a way to change those ethics!
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.
A new flood vulnerability index adapted for the pre-Saharan region
Published in International Journal of River Basin Management, 2021
Ahmed Karmaoui, Stefania Balica
Pre-Saharan North Africa constitutes a major indicator of climatic trends in the Mediterranean region; is currently experiencing a rapid climatic deterioration and desertification (RBOSM 2008). This situation makes the region (Figure 2) a vulnerable area. Since the middle of the twentieth century, oases have borne increasing demographic and investment pressures resulting in larger water abstraction, soil salinization, loss of surrounding vegetation and soil erosion (MEA 2005).