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A short class with Sarah and her students. The other ways are under More.
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Let’s start with the Water Budget Method. Can anyone tell me how this method works?
Does it focus on inflow and outflow?
Exactly! The formula is E = I + P - O - ΔS, which helps us calculate evaporation when we know the inflow, precipitation, outflow, and change in storage. Remember, 'I' stands for inflow!
So, we can monitor lakes or reservoirs to apply this method?
Correct! This method is especially useful for large bodies of water. It’s a great way to estimate evaporation without direct measurement.
Can we use this in smaller systems like ponds?
Good question! While it can be applied to smaller systems, accuracy may be affected if all variables aren't measured accurately. Always consider the scale!
In summary, the Water Budget Method is a practical approach for estimating evaporation from monitored water bodies, focusing on the continuity equation.
Next, let's delve into the Energy Budget Method. Who can explain what it relies on?
The conservation of energy, right?
Absolutely! It calculates evaporation based on net radiation input. The formula is E = (Rn - H - G) / λ. Can anyone break down what those terms mean?
I think Rn is net radiation?
Correct! And H is the sensible heat transfer, while G stands for ground heat flux. Lastly, λ represents the latent heat of vaporization. Understanding these components helps us see how energy drives evaporation.
So, if we have higher net radiation, we would expect more evaporation?
Yes! Increased energy availability enhances evaporation rates. Always remember that!
In summary, the Energy Budget Method uses conservation of energy principles to estimate evaporation based on energy inputs and outputs. It's critical for areas where direct measurement is impractical.
Now, let’s tackle the Penman Equation. Who knows what differentiates this equation from others?
Does it include more factors like atmosphere and energy?
Exactly! The Penman Equation combines both energy and aerodynamic components. The formula is E = (ΔR + γf(u)(es - ea)) / (Δ + γ). Can anyone express what Δ and γ represent?
I think Δ is the slope of the vapor pressure curve and γ is the psychrometric constant?
Spot on! And f(u) represents the wind function, which is crucial in incorporating atmospheric conditions. This comprehensive approach enhances accuracy.
So, this equation works well for varied conditions?
Absolutely, it’s versatile! By integrating multiple factors, it’s suitable for diverse climatic conditions.
In summary, the Penman Equation is a holistic method for estimating evaporation, factoring in both energy and atmospheric conditions to improve estimation reliability.
Lastly, let’s discuss some empirical formulas like Mayer’s and Rohwer’s equations. Why do we use these?
They probably give quick estimates without big setups?
Exactly! Mayer’s Formula and Rohwer’s Equation provide simplified evaporation estimates, especially where data is limited. Can anyone recall what variables are included?
I know Mayer's involves saturated vapor pressure and actual vapor pressure.
Correct! It’s E = K(ew - ea)(1 + u/16), where K is a coefficient that adjusts for location and season. Rohwer’s equation is similar but has its form too.
Why is it essential to have wind speed in those formulas?
Great thinking! Wind speed affects evaporation rates significantly, which is why it’s included. It’s essential for accuracy.
In summary, empirical formulas like Mayer’s and Rohwer’s offer quick estimation tools, relying on data availability, particularly wind speed and vapor pressures.
Estimating evaporation using inflow, precipitation, outflow, and storage.
Estimates evaporation based on conservation of energy principles.
A comprehensive estimate using energy and aerodynamic factors.
Quick estimation tools for evaporation using atmospheric data.
Evaporation flows, from water to air, Energy and wind, do show we care.
Once upon a time, in a large lake, water wished to fly. By absorbing energy from the sun and being pushed by wind, it transformed into vapor, escaping into the sky.
Remember the acronym 'PEWE' for evaporation: P for Precipitation, E for Energy, W for Wind, E for Evaporation. Each is a key factor!
W.E.T. for Water Budget: W for Water inflow, E for Evaporation, T for Totals in and out.
Term
Water Budget Method Formula
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Term
Energy Budget Method
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Penman Equation
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Empirical Formula Example
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The process by which water changes from liquid to vapor due to energy absorption.
A method for estimating evaporation based on the continuity equation involving inflow, precipitation, outflow, and change in storage.
Estimation of evaporation based on conservation of energy where net radiation input is measured.
An equation combining energy and aerodynamic terms to estimate evaporation.
Simplified equations that relate evaporation to measurable atmospheric variables.
This section discusses methods to estimate evaporation when direct measurement is impractical, highlighting techniques such as the Water Budget Method, Energy Budget Method, Penman Equation, and various empirical formulas.
When direct measurement of evaporation is not feasible, several empirical and analytical methods are employed for estimation. This section outlines important techniques, including the Water Budget Method, which relies on inflow and outflow assessments, and the Energy Budget Method, which conserves energy principles. The Penman Equation combines energy and aerodynamic factors to provide a more comprehensive calculation of evaporation.
In situations where direct measurement of evaporation is challenging, various methods are used to estimate evaporation based on different principles. This section focuses on several notable techniques:
This method uses the continuity equation:
E = I + P - O - ΔS
where:
This technique is particularly beneficial for large lakes or reservoirs where monitoring inflow and outflow is feasible.
Based on the principle of energy conservation, this method calculates evaporation from:
E = (Rn - H - G) / λ
where:
This approach provides insights into the energy dynamics involved in evaporation.
The Penman Equation factors in both energy and atmospheric conditions:
E = (ΔR + γf(u)(es - ea)) / (Δ + γ)
where:
This equation is comprehensive as it integrates multiple components affecting evaporation.
These include:
Mayer’s Formula: E = K (ew - ea)(1 + u/16) where:
Rohwer’s Equation: E = 0.771(ew - ea)(1 + 0.536u)
Such empirical formulas are applicable where data regarding wind speed and vapor pressure is available, showcasing the variety of techniques available to estimate the evaporation process.