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2012 | Buch

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Evapotranspiration in the Soil-Plant-Atmosphere System

verfasst von: Viliam Novák

Verlag: Springer Netherlands

Buchreihe : Progress in Soil Science

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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Über dieses Buch

Evapotranspiration and its components (evaporation and transpiration) as a process is one of the basic terms of Earth's water balance; its importance is accented by the fact that transpiration is the vital element of the biomass production process. The second important property of evapotranspiration is its extreme consumption of solar energy, thus controlling the temperature of the atmosphere and creating favourable conditions for life. Evapotranspiration as an energy consuming process is also the connection between the energy and mass cycles of the Earth. Evapotranspiration is a process performing in the Soil–Plant –Atmosphere System (SPAS); therefore this book is presenting and quantifying it as a catenary process, describing transport of water in the soil, including root extraction patterns and methods of its evaluation. Transport of water through the plant and from the canopy to the atmosphere is also described and quantified. A variety of evapotranspiration (and its components evaporation and transpiration) calculation methods are described, starting from empirical methods up to the most sophisticated ones based on the solution of the transport equations of water and energy in the SPAS. The most important (and widely used) calculation method - modified Penman–Monteith method is described in details, ready to be used with data in the book only. Water balance method of evapotranspiration estimation as well as sap flow method description can be found in the book as well. The book can be used by hydrologists, biologists, meteorologists and other specialists as well as by ecology students.

Key themes: soil hydrology – evapotranspiration – hydropedology– plant physiology – water movement in soils – evaporation – transpiration

Dr. Viliam Novák is a water resources scientist at the Institute of Hydrology of the Slovak Academy of Sciences in Bratislava (Slovakia).

Inhaltsverzeichnis

Frontmatter

Chapter 1. Evapotranspiration: A Component of the Water Cycle

Abstract

Evapotranspiration as a process is part of the water cycle of the Earth; it is the most important consumer of energy, creating the link between water and energy cycles of the Earth. The physics of water phase change is briefly presented. Consumption of energy to change liquid water into water vapor cools the biosphere, thus allowing the creation of suitable conditions for life on the Earth. This chapter contains basic information about the Earth and continents’ water cycle and its components, as well as the energy balance structure of the Earth. The kinetic theory of fluids is used to quantify the evaporation process because it depends on the properties of an environment, allowing us to find the most important properties of the environment influencing evapotranspiration. The kinetic theory of evaporation can help us understand evaporation as a process, but does not allow use in directly quantifying it; therefore other methods should be used.

Viliam Novák

Chapter 2. Soil-Plant-Atmosphere System

Abstract

Water can evaporate from all wet surfaces if there is a flux of energy. The most important process for biomass production and proper functioning of the biosphere is evapotranspiration. Evapotranspiration is, however, the process of water transport through the soil-plant-atmosphere system (SPAS). Every subsystem of the SPAS can strongly influence the evapotranspiration process. This chapter contains basic information about all three subsystems of the SPAS. Basic properties of water (water vapor), soil, plant (canopy), and atmosphere are presented and their role in the evapotranspiration process is discussed. It is shown that soil water is not pure water but a solute, and salinization during evapotranspiration can occur. The role of carbon dioxide and its increase in the SPAS is discussed, mainly the possible effect of carbon dioxide on the greenhouse effect.

Viliam Novák

Chapter 3. Evaporation from Different Surfaces

Abstract

Water evaporates from different, wet surfaces. This chapter briefly describes water evaporation from various evaporating surfaces and their specific features are accented. Evaporation of intercepted water, evaporation from water surfaces, from snow and ice as well as evaporation from urbanized surfaces is described. Transpiration as a process of water transport from soil through plant to the atmosphere is discussed. The basic features of water transport through plants and properties of roots and leaves (stomata) are given, to better understand the transpiration process. The term potential evapotranspiration, as well as potential transpiration (evaporation), is described and quantified. Conditions necessary for potential evapotranspiration are presented and the process of potential transpiration is defined. Finally, the term potential evapotranspiration index is described.

Viliam Novák

Chapter 4. Transport of Water and Energy in the Boundary Layer of the Atmosphere

Abstract

The boundary layer of the atmosphere (BLA) is the space above the Earth, properties of which are strongly influenced by the Earth surface. Water vapor evaporating from the surface is transported in the BLA; therefore, the properties of the BLA can strongly influence the evapotranspiration process. Vertical distributions of the meteorological characteristics (wind, air humidity, and air temperature profiles) in this layer are described quantitatively. Parameters of those profiles as well as methods of their evaluation are presented. Parameters of the evaporating surface (roughness length, zero displacement level) are described as well as methods of their estimation. Transport properties of the BLA are of primary importance and can be expressed by transport coefficients. Methods of heat and water vapor transport coefficients estimation in the BLA are described. The influence of the state of an atmosphere on transport coefficients is discussed and the method of its quantification is given.

Viliam Novák

Chapter 5. Movement of Water in Soil During Evaporation

Abstract

Evaporation is a catenary process, during which water is transported through the Soil-Plant-Atmosphere System (SPAS). One subsystem of SPAS is soil, which accumulates water and transports it to the roots (transpiration) or to the soil surface where water is evaporating. In this chapter, movement of water in the soil subsystem is described. Movement of soil water during evaporation is a nonisothermal process in principle; soil is heated by the energy of the Sun and cooled by the energy consumed during evaporation. Typical soil water content (SWC) profiles during evaporation are presented, demonstrating their typical features during isothermal and nonisothermal evaporation. Typical relationships of evaporation and soil water content estimated in the field and in the laboratory are given, and the three stages of evaporation as they are related to the SWC are identified. A system of equations describing movement of liquid water, water vapor, and heat in the soil and approximative solution of transport equation for bare soil are presented.

Viliam Novák

Chapter 6. Movement of Water in the Soil Root Zone During Transpiration

Abstract

Movement of soil water during transpiration is a complicated process in comparison to evaporation because the root system of plants extracts water (and solute) from the soil using the soil root layer. Evaporation is the typical movement of water to the soil surface (or close to it) from which water is evaporating. The properties of different plants’ root systems and their changes during ontogenesis is described, as well as the influence of different environmental factors on root growth and properties. Richards’ equation describing soil water movement with root extraction is presented. The method of root extraction rate of water estimation from soil water content (SWC) field measurements is presented. This is the proposed method of water uptake evaluation by roots, based on the results of field measurements. This method is used to model water movement and extraction by roots in soil with a plant canopy. The mesoscopic approach to water uptake by an evaluation of roots is described.

Viliam Novák

Chapter 7. The Role of Plants in Transport Processes in the Soil-Plant-Atmosphere System

Abstract

The role of a plant is to reproduce itself. Transport of water from soil through plant and to the atmosphere is a part of this process. Water consumption in the photosynthetic process is small in comparison with transpiration, which is enormous, and transpirating water passes through the plant and stomata to the atmosphere. To preserve itself, the plant can regulate transpiration by stomata opening and closing. Water movement through the plant is described and quantified, with emphasis on the role of stomata in the transpiration process. The resistance (or conductivity) of stomata is defined and methods of their measurement and estimation are described, as well as the resistance of plants and canopies. Daily and seasonal leaf resistance courses are shown. The relations between leaf resistance and properties of an environment are presented. Semiempirical formulas to quantify canopy resistance are also given.

Viliam Novák

Chapter 8. Evapotranspiration and Soil Water

Abstract

Evapotranspiration rate from a given evaporating surface depends on the properties of the atmosphere only, if water is not a limiting factor. Transport of water to the evaporation surface or to the roots sometimes cannot cover potential evapotranspiration needs. The reason is the low hydraulic conductivity of the soil due to low soil water potential in the soil root zone. Then the evapotranspiration rate is less than the potential one, and the relationship between evapotranspiration rate and soil water potential of the root zone can be found and applied to calculate actual evapotranspiration. Empirically estimated relationships between relative transpiration (evaporation) are given and generalized, to allow calculation of actual transpiration (evaporation) from potential data calculated using standard meteorological data. Using the relationship between relative transpiration (evaporation) to calculate actual data is preferred, because of easy evaluation of it in comparison with soil water potential.

Viliam Novák

Chapter 9. Methods of Evapotranspiration Estimation

Abstract

Contemporary methods of evapotranspiration estimation are described in detail, along with transpiration and evaporation. Measurement of evapotranspiration by lysimeters (from bare soil or soil with a canopy) and measurement of evaporation from a water table are described. A wide variety of evapotranspiration calculation systems are presented, starting with the soil water balance method. These include a group of micrometeorological techniques to which belong turbulent diffusion, energy balance, eddy correlation, and the so-called combination method, which combines water vapor and sensible heat transport equations and the energy balance equation at the evaporating surface. The Penman and Penman-Monteith approaches also belong to this group of procedures. Many empirical equations allow potential evapotranspiration calculation with limited data input. A method of tree transpiration estimation using sap flow measurement is described.

Viliam Novák

Chapter 10. Evapotranspiration Components Structure

Abstract

The term evapotranspiration structure denotes separation into two basic components: transpiration (water movement through and from plants) and evaporation (from other surfaces). An approximative method of evapotranspiration structure calculation is presented. It is based on the empirically estimated relationship between the canopy leaf area index (LAI) and relative potential transpiration, i.e., on the ratio of potential transpiration and potential evapotranspiration. It was found that this relationship can be used universally for a wide variety of crops. Typical daily and seasonal courses of the evapotranspiration structure elements of crops are demonstrated, i.e., increasing transpiration rate with LAI and, conversely, decreasing evaporation rate with LAI increase. The proposed method of potential evapotranspiration structure calculation is involved in the proposed method of evapotranspiration calculation.

Viliam Novák

Chapter 11. Combination Method of Daily Evapotranspiration Calculation

Abstract

The method presented to calculate evapotranspiration daily total allows estimation of it and its components (transpiration, evaporation) from homogeneous evaporating surfaces. The method denoted as combination method is based in principle on the Penman-Monteith equation with modifications in calculation canopy resistance (using the Obuchov-Monin approach) and using empirical formulas to calculate evapotranspiration structure. Calculation is done using the so-called two-step method: potential evapotranspiration is calculated first, and the actual value is calculated using the relative evapotranspiration soil water content relationship. Input data necessary to calculate it are plant characteristics (roughness length, leaf area index), standard meteorological data (air temperature, air humidity, sunshine duration, wind velocity), and soil root zone water content. Latitude of the site is needed to calculate net radiation. This chapter contains all the necessary tables needed to calculate daily rates of evapotranspiration; no other sources are needed.

Viliam Novák

Chapter 12. Estimation of Regional Evapotranspiration Using Remote Sensing Data

Abstract

Contemporary progress in remote sensing techniques provides the opportunity to use data acquired by this method in the calculation of regional evapotranspiration. The weak point of traditional methods is the necessity to measure soil-plant-atmosphere system (SPAS) data at separate sites and upscale the information for regional evapotranspiration calculation. Many authors tried to use these data from the earliest days of the remote sensing technique. The problem is that traditional methods were used, and the question is how to use the data acquired by remote sensing techniques to calculate evapotranspiration. Two methods of evapotranspiration calculation are described herein that use remotely estimated data. One is the simplified energy balance method and the other uses the so-called complementary relationship. It is recommended that these methods be applied to upscale evapotranspiration data, although their accuracy is relatively poor.

Viliam Novák

Backmatter

Titel: Evapotranspiration in the Soil-Plant-Atmosphere System
verfasst von: Viliam Novák
Verlag: Springer Netherlands
Electronic ISBN: 978-94-007-3840-9
Print ISBN: 978-94-007-3839-3
DOI: https://doi.org/10.1007/978-94-007-3840-9