10: Evaporation and Wind Erosion
- Page ID
- 38741
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Thus far we have studied the spatial patterns and organization of soils across multiple spatial scales, and we have examined how soils interact with water balance processes such as precipitation, rainfall interception, raindrop impact, infiltration, runoff, water erosion, soil water redistribution, drainage, solute transport, and groundwater pollution.Now, we are ready to move toward the right-hand side of Fig. 10-1 to consider the processes connected to the energy balance at the land surface.
In this chapter, we will focus on the process of evaporation. In this context, evaporation is the process in which water changes phase from liquid to vapor and is transported to the atmosphere from one of the following sources:
•the soil,
•the exterior surface of plants,
•plant residue, or
•surface water bodies.
Defined in this way, evaporation is distinct from the process of transpiration, which is the vaporization of water from the interior of plants,predominantly exiting through the stomata. The above definition also distinguishes evaporation from the composite process called evapotranspiration, which is simply the sum of evaporation and transpiration for a specified region of the Earth’s surface.Here is an audio overview to help begin our study [website].
- 10.1: Necessary conditions for evaporation
- When you think of evaporation, you likely think of the energy supply for evaporation as coming from the sun. And, that is typically the primary energy source. But, it is important to recognize that the energy supply can also be drawn from the body undergoing evaporation, e.g. the soil, or from its surroundings, e.g. the air. That is why sweat evaporating from our body helps to cool us down. That is also why evaporation can occur even during the nighttime.
- 10.2: Evaporation from a water table
- Salinization is the accumulation of salts in the soil to a level that negatively impacts agricultural production, ecosystem health, and economic welfare [1]. Soil salinization contributed to the downfall of ancient societies in Mesopotamia [2], and it currently affects approximately 397 Mha worldwide or 3.1% of Earth’s land area [3]. Understanding the physics of evaporation from a shallow water table can help us better understand the related process of salinization.
- 10.3: Evaporation in the absence of a water table
- During the first stage, the evaporation is limited by the evaporative demand, and the soil is able to transmit water to the soil surface at a rate adequate to meet that demand. If the evaporative demand is constant during this stage, then the evaporation rate will be constant as well. That is the situation illustrated in the laboratory data shown in Fig. 10‑4 [5]. However, in field situations the evaporative demand typically follows a daily cycle, with peak demand near midday and minimum values
- 10.4: Reducing evaporative losses
- Evaporation from the soil can consume a substantial portion of the available water in cropping systems, and farmers have often sought methods to reduce evaporative losses. One effective method to conserve water during the first stage of evaporation is to keep the soil covered with crop residues. Crop residues on the surface reduce the amount of solar radiation reaching the surface and can reduce the rate of water vapor transport away from the surface, both of which lower the evaporative....
- 10.5: Wind erosion
- Tillage was also considered by some to provide a means of reducing evaporative losses and conserving soil water. They reasoned that if a shallow surface layer of the soil was pulverized and desiccated by tillage, then the hydraulic conductivity of that layer would be so low, that soil water in the underlying layers would be protected from evaporation. T
- 10.6: Problem set
- Calculate the maximum steady-state evaporation rate in mm d-1 for a sandy loam with a water table depth of 1.0 m, with b = 4 .7, Ψe = -14.7 cm, and Ks = 1.60 cm h -1.
- 10.7: References
- Rengasamy, P., World salinization with emphasis on Australia. Journal of Experimental Botany, 2006. 57(5): p. 1017-1023. Jacobsen, T. and R.M. Adams, Salt and silt in ancient Mesopotamian agriculture. Science, 1958. 128(3334): p. 1251-1258. Setia, R., et al., Soil salinity decreases global soil organic carbon stocks. Science of The Total Environment, 2013. 465: p. 267-272.