This document discusses evaporation and evapotranspiration. It provides terminology for evaporation, transpiration, and evapotranspiration. Factors controlling evaporation include meteorological factors like solar radiation, relative humidity, temperature, and wind, as well as the nature of the evaporating surface. Methods to estimate evaporation include water budget, energy budget, mass transfer, combination methods, and evaporation formulas. Evaporation from free water surfaces can be estimated using these methods or evaporation pans with a pan coefficient. The document also discusses potential and actual evapotranspiration and methods to estimate them, including the Penman-Monteith equation and empirical methods.
The following file contains contents regarding Evaporation. Different methods to measure evaporations.
Primarily three methods are mentioned to measure Evaporation, that is Empirical Methods, Analytical Methods, and By using Evaporimeter or Pan.
Evaporation is a process by which water changed from the liquid or solid state into the gaseous state through the absorption of heat
It is always related to the loss of water from a free surface over a fixed time interval. Either direct observation or calculation based on the factors involved in the transfer of thermal energy.
One of the fundamental component of hydrological cycle
Essential requirements in the process are
The source of energy to vaporize the liquid water (solar or wind)
The presence of gradient of concentration between the evaporating surface and the surrounding air.
The following file contains contents regarding Evaporation. Different methods to measure evaporations.
Primarily three methods are mentioned to measure Evaporation, that is Empirical Methods, Analytical Methods, and By using Evaporimeter or Pan.
Evaporation is a process by which water changed from the liquid or solid state into the gaseous state through the absorption of heat
It is always related to the loss of water from a free surface over a fixed time interval. Either direct observation or calculation based on the factors involved in the transfer of thermal energy.
One of the fundamental component of hydrological cycle
Essential requirements in the process are
The source of energy to vaporize the liquid water (solar or wind)
The presence of gradient of concentration between the evaporating surface and the surrounding air.
soil plant water relationship determinationhailu55
The relationship is related to the properties of soil and plants
that affect the movement, retention and use of water.
A simple analogy:
Soil – Water Reservoir
Plant Roots – pump with many inlets
As the rate of pumping depends on the character of the pump,
the rate of extraction of water from the soil by the plant depends
on the character of the soil.
Soil Water Classification
Gravitational water:
It is the water in the large pores that moves downward freely under the influence of gravity
It drains out so fast that it is not available to the crops.
The time of draining out varies from one day in sandy soils to three days in clay soils.
Capillary Water:
It is the amount of water retained by the soil after gravitational water has drained out.
It is the water in the small pores which moves because of capillary forces and is called capillary water.
Capillary water is the major source of water available for the plant
Hygroscopic Water
Soil moisture further reduced by ET until no longer moves because of capillary forces.
The remaining water which is held on particle surfaces so tightly is called hygroscopic water.
Here, the water is held by adhesive force. And therefore, it is unavailable to the plant.
soil water constants
Field Capacity (FC)
Following saturation when all macro pores are drained by gravity and drainage ceases, usually defined 2 days following saturation by rainfall.
Measured as the moisture content at -5 kPa (0.05 bar or 0.5 m tension)
Permanent Wilting point (PWP)
The point where plants cannot extract any more water – only very small pores are filled with water.
Defined as the moisture content at -1500 kPa (15 bar or 150 m tension)
Total Available Water
Total Available Water (TAW): the water available to crops
expressed in mm/m (mm of water per meter depth of soil).
TAW = (FC – PWP)*b*Dz
Readily Available Water (RAW):
This is the level to which the available water in the soil can be used up without causing stress in the crop.
For most crops, 50 to 60% of the total available water is taken as readily available.
RAW = MAD*TAW
Where, MAD = maximum allowable deficit
Crop Water Requirement
CU is the controlling factor for irrigation scheduling.
That is, CU determines the quantity of water to be added by irrigation and helps in day to day management of irrigation systems.
Actually, total water demand of crops is made up of:
i) Crop water use: includes evaporation and transpiration
ii) Leaching requirement: a fraction of water to be added to remove salts from the root zone.
iii) Losses of water due to deep seepage in canals and losses due to the inefficiency of application.
ETc = Evaporation + Transpiration
ETc is normally expressed in mm/day.
Factors Affecting ETc:
Weather parameters (To, RH, Wind, etc.)
Crop Characteristics (type, variety and length of growing period)
Management and Environmental aspects
(control of diseases, soil salinity, etc.)
soil plant water relationship determinationhailu55
The relationship is related to the properties of soil and plants
that affect the movement, retention and use of water.
A simple analogy:
Soil – Water Reservoir
Plant Roots – pump with many inlets
As the rate of pumping depends on the character of the pump,
the rate of extraction of water from the soil by the plant depends
on the character of the soil.
Soil Water Classification
Gravitational water:
It is the water in the large pores that moves downward freely under the influence of gravity
It drains out so fast that it is not available to the crops.
The time of draining out varies from one day in sandy soils to three days in clay soils.
Capillary Water:
It is the amount of water retained by the soil after gravitational water has drained out.
It is the water in the small pores which moves because of capillary forces and is called capillary water.
Capillary water is the major source of water available for the plant
Hygroscopic Water
Soil moisture further reduced by ET until no longer moves because of capillary forces.
The remaining water which is held on particle surfaces so tightly is called hygroscopic water.
Here, the water is held by adhesive force. And therefore, it is unavailable to the plant.
soil water constants
Field Capacity (FC)
Following saturation when all macro pores are drained by gravity and drainage ceases, usually defined 2 days following saturation by rainfall.
Measured as the moisture content at -5 kPa (0.05 bar or 0.5 m tension)
Permanent Wilting point (PWP)
The point where plants cannot extract any more water – only very small pores are filled with water.
Defined as the moisture content at -1500 kPa (15 bar or 150 m tension)
Total Available Water
Total Available Water (TAW): the water available to crops
expressed in mm/m (mm of water per meter depth of soil).
TAW = (FC – PWP)*b*Dz
Readily Available Water (RAW):
This is the level to which the available water in the soil can be used up without causing stress in the crop.
For most crops, 50 to 60% of the total available water is taken as readily available.
RAW = MAD*TAW
Where, MAD = maximum allowable deficit
Crop Water Requirement
CU is the controlling factor for irrigation scheduling.
That is, CU determines the quantity of water to be added by irrigation and helps in day to day management of irrigation systems.
Actually, total water demand of crops is made up of:
i) Crop water use: includes evaporation and transpiration
ii) Leaching requirement: a fraction of water to be added to remove salts from the root zone.
iii) Losses of water due to deep seepage in canals and losses due to the inefficiency of application.
ETc = Evaporation + Transpiration
ETc is normally expressed in mm/day.
Factors Affecting ETc:
Weather parameters (To, RH, Wind, etc.)
Crop Characteristics (type, variety and length of growing period)
Management and Environmental aspects
(control of diseases, soil salinity, etc.)
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Willie Nelson Net Worth: A Journey Through Music, Movies, and Business Venturesgreendigital
Willie Nelson is a name that resonates within the world of music and entertainment. Known for his unique voice, and masterful guitar skills. and an extraordinary career spanning several decades. Nelson has become a legend in the country music scene. But, his influence extends far beyond the realm of music. with ventures in acting, writing, activism, and business. This comprehensive article delves into Willie Nelson net worth. exploring the various facets of his career that have contributed to his large fortune.
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Introduction
Willie Nelson net worth is a testament to his enduring influence and success in many fields. Born on April 29, 1933, in Abbott, Texas. Nelson's journey from a humble beginning to becoming one of the most iconic figures in American music is nothing short of inspirational. His net worth, which estimated to be around $25 million as of 2024. reflects a career that is as diverse as it is prolific.
Early Life and Musical Beginnings
Humble Origins
Willie Hugh Nelson was born during the Great Depression. a time of significant economic hardship in the United States. Raised by his grandparents. Nelson found solace and inspiration in music from an early age. His grandmother taught him to play the guitar. setting the stage for what would become an illustrious career.
First Steps in Music
Nelson's initial foray into the music industry was fraught with challenges. He moved to Nashville, Tennessee, to pursue his dreams, but success did not come . Working as a songwriter, Nelson penned hits for other artists. which helped him gain a foothold in the competitive music scene. His songwriting skills contributed to his early earnings. laying the foundation for his net worth.
Rise to Stardom
Breakthrough Albums
The 1970s marked a turning point in Willie Nelson's career. His albums "Shotgun Willie" (1973), "Red Headed Stranger" (1975). and "Stardust" (1978) received critical acclaim and commercial success. These albums not only solidified his position in the country music genre. but also introduced his music to a broader audience. The success of these albums played a crucial role in boosting Willie Nelson net worth.
Iconic Songs
Willie Nelson net worth is also attributed to his extensive catalog of hit songs. Tracks like "Blue Eyes Crying in the Rain," "On the Road Again," and "Always on My Mind" have become timeless classics. These songs have not only earned Nelson large royalties but have also ensured his continued relevance in the music industry.
Acting and Film Career
Hollywood Ventures
In addition to his music career, Willie Nelson has also made a mark in Hollywood. His distinctive personality and on-screen presence have landed him roles in several films and television shows. Notable appearances include roles in "The Electric Horseman" (1979), "Honeysuckle Rose" (1980), and "Barbarosa" (1982). These acting gigs have added a significant amount to Willie Nelson net worth.
Television Appearances
Nelson's char
"Understanding the Carbon Cycle: Processes, Human Impacts, and Strategies for...MMariSelvam4
The carbon cycle is a critical component of Earth's environmental system, governing the movement and transformation of carbon through various reservoirs, including the atmosphere, oceans, soil, and living organisms. This complex cycle involves several key processes such as photosynthesis, respiration, decomposition, and carbon sequestration, each contributing to the regulation of carbon levels on the planet.
Human activities, particularly fossil fuel combustion and deforestation, have significantly altered the natural carbon cycle, leading to increased atmospheric carbon dioxide concentrations and driving climate change. Understanding the intricacies of the carbon cycle is essential for assessing the impacts of these changes and developing effective mitigation strategies.
By studying the carbon cycle, scientists can identify carbon sources and sinks, measure carbon fluxes, and predict future trends. This knowledge is crucial for crafting policies aimed at reducing carbon emissions, enhancing carbon storage, and promoting sustainable practices. The carbon cycle's interplay with climate systems, ecosystems, and human activities underscores its importance in maintaining a stable and healthy planet.
In-depth exploration of the carbon cycle reveals the delicate balance required to sustain life and the urgent need to address anthropogenic influences. Through research, education, and policy, we can work towards restoring equilibrium in the carbon cycle and ensuring a sustainable future for generations to come.
Characterization and the Kinetics of drying at the drying oven and with micro...Open Access Research Paper
The objective of this work is to contribute to valorization de Nephelium lappaceum by the characterization of kinetics of drying of seeds of Nephelium lappaceum. The seeds were dehydrated until a constant mass respectively in a drying oven and a microwawe oven. The temperatures and the powers of drying are respectively: 50, 60 and 70°C and 140, 280 and 420 W. The results show that the curves of drying of seeds of Nephelium lappaceum do not present a phase of constant kinetics. The coefficients of diffusion vary between 2.09.10-8 to 2.98. 10-8m-2/s in the interval of 50°C at 70°C and between 4.83×10-07 at 9.04×10-07 m-8/s for the powers going of 140 W with 420 W the relation between Arrhenius and a value of energy of activation of 16.49 kJ. mol-1 expressed the effect of the temperature on effective diffusivity.
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A brief about organic farming/ Natural farming/ Zero budget natural farming/ Subash Palekar Natural farming which keeps us and environment safe and healthy. Next gen Agricultural practices of chemical free farming.
2. 3. Evaporation and Evapotranspiration
3.1 Factors controlling evaporation
3.2 Evaporation from free water surface
3.3 Estimation of evaporation and evapotranspiration
3. 3. Evaporation and Evapotranspiration
Terminology
Evaporation – the process through which water is transferred from the surface of
the Earth to the atmosphere
Transpiration - the water loss from the plants, through the pores at the surface
of their leaves
Evapotranspiration – Evaporation + Transpiration
Evaporation is important in all areas of water resources because it affects:
The capacity of the reservoir,
The yield of river basin,
The consumptive use of water
4. It is the maximum amount of water that could be evapotranspirated at a site.
Potential Evapotranspiration (PET):
Index of dryness or aridity index (AI):
𝑃𝐸𝑇: mean annual potential evapotranspiration
𝑃: mean annual precipitation
𝐴𝐼 =
𝑃𝐸𝑇
𝑃
5. a) Meteorological factors
b) The nature of the evaporating surface
3.1 Factors controlling evaporation
a) Meteorological factors
Solar radiation:
Evaporation is a process of energy exchange.
Solar radiation supply the energy necessary for the liquid water
molecules to evaporate.
Relative humidity:
As the humidity of air increases its ability to absorb more water
vapor decreases, and the rate of evaporation becomes slower.
6. The temperature of air:
Temperature increase saturation vapor pressure (increases saturation deficit),
high temperature implies that there is energy available for evaporation.
Wind:
As the liquid water vaporizes from a water body, the air adjacent to this body
will be saturated. For the continuation of evaporation, this saturated air should
be removed by wind.
10% change in the wind speed 1-3% change in evaporation.
7. b) The nature of the evaporating surface
Temperature of liquid water:
High liquid water temperature
High molecular motion in the water
The number of molecules leaving the water body will be high
Salinity:
Adversely affects evaporation
1% increase in salt concentration 1% decrease in evaporation
Reflection coefficient (albedo) of the surface:
High albedo Low evaporation from the surface
8. In general, the two main factors that affect evaporation from an open water
surface are: the supply of energy (solar radiation) and the ability to transport the
vapor away from the evaporative surface (depends on the wind velocity).
The potential evapotranspiration (PET) is the evapotranspiration that would occur
from a well vegetated surface when moisture supply is not limiting, and this is
calculated in a very similar to that for open water evaporation.
Actual evapotranspiration drops below its potential level as the soil dries out.
Potential evapotranspiration (PET) is
defined as the amount of ET that would
occur if a sufficient water source were
available.
Actual ET (AET) is limited by the actual soil
moisture. It might be smaller than PET.
9. Evaporation
How to measure it?
Mass Balance – account for all inflows, all
outflows
Land Pan (4ft diameter, 10 inches deep
unpainted galvanized metal)
Daily records of depth of water,
precipitation, replacement water and
wind record – empirical relationships
10. Problems
o Averages (One daily/weekly/monthly vs.
Continuous)
o Highly variable depending on conditions
o What does a pan tell us about say something
the size of a lake?
o Empirical Corrections – EMPIRICAL!!
o Works well in lab where conditions are well
controlled, but real life is not so simple
o Penman Formula (Semi-Empirical)
11. Transpiration
Transpiration is the process by which moisture is
carried through plants from roots to small pores
on the underside of leaves, where it changes to
vapor and is released to the atmosphere.
Transpiration is essentially evaporation of water
from plant leaves.
Studies have revealed that about 10 percent of
the moisture found in the atmosphere is released
by plants through transpiration.
12. Evapotranspiration
In the field it is next to impossible to
distinguish between evaporation and
transpiration so we lump them together.
From a water budget perspective we
don’t care too much about the details
How to measure it?
13. The estimation of evaporation from free water surfaces is necessary for mainly two
purposes:
3.2 Evaporation from free water surface
a) The determination of actual evaporation taking place from an existing
reservoir for an optimum operation of the reservoir.
b) The estimation of future evaporation from a reservoir to be constructed.
The evaporation from free water surface can be estimated using evaporation pans
14. Evaporation from water surfaces can be determined by:
1) Water budget
2) Energy budget
3) Mass transfer methods
4) Combination methods
5) Evaporation formulas
Water Budget?
The water-budget equation for estimating evaporation can be written as:
𝐸 = 𝐼 + 𝑃 − 𝑂 − 𝑂𝑆 + ∆𝑆
Where, E =Evaporation, I = Inflow, P = Precipitation, O = Outflow, Os = Seepage
and ΔS = Change in storage
15. Water budget (storage equation) approach
This method consists of drawing up a balance sheet of all the water entering and
leaving a particular catchment or drainage basin.
Continuity Equation:
where
∆S : change in storage (S2 – S1)
P: precipitation
QS: surface inflow
Q0: surface outflow
QSS: subsurface outflow (seepage)
∆t: week, month or year.
16. Energy budget method
where
QN: net radiation absorbed by the water body
Qh: sensible heat transfer
Qe: energy used for evaporation
Q: increase in energy stored in the water body
QV: advected energy of inflow and outflow
𝑄𝑁 = 𝑄𝑠 − 𝑄𝑟 − 𝑄𝑏
𝑄𝑁 − 𝑄ℎ − 𝑄𝑒 = 𝑄𝜃 − 𝑄𝑉
where
Qs: shortwave solar radiation
Qr: shortwave reflected radiator
Qb: longwave radiation to atmosphere
where
ρ: density of water (gr/cm3)
Le: latent heat of vaporization (cal/gr)
R : ratio of heat loss by conduction to
that by evaporation
𝐸 =
𝑄𝑁 + 𝑄𝑉 − 𝑄𝜃
𝜌𝐿𝑒 1 + 𝑅
𝑅 = 𝛾
𝑇𝑠 − 𝑇𝑎
𝑒𝑠 − 𝑒𝑎
where
γ : Psychrometer constant = 0.66 mb/°C.
Ts: water surface temperature in °C.
Ta: air temperature in °C.
es: saturation vapor pressure in mb.
ea: vapor pressure of the air in mb
17. The following empirical aerodynamic equation was proposed by Dalton to estimate
the evaporation of open water
𝐸𝑜 = 𝑓(𝑈)(𝑒𝑠 − 𝑒𝑑)
where f(U) is a function of the wind speed, es is the saturation vapor pressure
corresponding to the temperature Ts of the laminar sub-layer at the surface, ed is
the actual vapor pressure of the air at a standard height (usually 2 m).
Some examples of the aerodynamic approach to compute Eo in mm/day are:
a) Ijssel Lake (the Netherlands)
𝐸𝑜 = 0.25(1 + 0.25𝑈6)(𝑒𝑤 − 𝑒𝑑)
b) Lake Hefner (USA)
𝐸𝑜 = 0.122𝑈4(𝑒𝑤 − 𝑒𝑑)
Mass transfer method
c) General equation (Harbeck, 1962)
𝐸𝑜 = 0.291𝐴−0.05
𝑈2(𝑒𝑤 − 𝑒𝑑)
• A is the size of the Lake in Mm2, ew is the saturation
vapor pressure for the temperature of the water.
18. Combined approach, the equation of Penman
Using energy budget and mass transport methods, Penman (1956) proposed a
new equation which gives a good estimation of evaporation from lakes for
daily to monthly periods:
where
E0: evaporation from open water surface (mm/day)
Qn: net amount of radiation remaining at the free water surface (g.cal/cm/day = 59 mm/day)
Ea: evaporation due to mass transfer of vapor (mm/day)
∆ : gradient of saturation vapor pressure at air temperature t (oC).
: Psychrometer constant (=0.66 mb/oC or 0.49 mm Hg / oC)
𝐸0 =
∆𝑄𝑛 + 𝛾𝐸𝑎
𝛾 + ∆
19. ∆ is determined as shown in the following figure.
20. Evaporation pans
At many meteorological stations the evaporation from a small water body (evaporation
pan) is usually monitored.
Evaporation is recorded from water level changes, corrected by rainfall depths.
Annual evaporation from a nearby lake is approximately 0.7 times the observation from
a pan.
This factor 0.7 is known as the pan coefficient and usually varied between 0.67 to 0.87.
The FAO uses pan evaporation data Epan to estimate the reference evaporation ETref as
follows:
ETref = kpan Epan
• Kpan is the pan coefficient usually vary between 0.35 to 0.85
21. • Surface area is 1m2 and water depth of 25cm
• The pan is filled with water to a depth of 20cm
• The decrease of water is measured by a point gage, which is
an evaporation rate.
• The pan is placed 15cm above the ground.
• Everyday water is added so that water surface is 5-8 cm
below the upper rim of the pan.
• Evaporation is the difference between the observed levels
• It is measured daily.
What is pan coefficient?
Pan evaporation
rates are higher than
actual values. That’s
why they have to be
adjusted with a
coefficient as 0.7
Evaporation pans
22. 3.3 Estimation of evaporation and evapotranspiration
Methods to estimate evaporation:
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23. Methods to estimate evapotranspiration:
Energy Methods (use parameters such as
solar radiation, soil heat flux, etc.)
Penman-Monteith equation
FAO56-Penman-Monteith method
Evaporation pans
Empirical Methods
Blaney-Criddle
Turc (1961)
Thornthwaite method
1) Potential evapotranspiration
Remote Sensing (satellite data)
Turc (1954)
Coutagne
Crop-coefficient method
(based on vegetation type,
albedo, surface resistance)
2) Actual evapotranspiration
24. Evaporation pan
Provide a direct measure of evaporation in the field
Pans measure the integrated effect of radiation, wind, temperature and humidity,
on the evaporation from open water surfaces
Water should be regularly renewed (at least once a week)
Water depth should be greater than 20 cm
Evaporation rates are sensitive to the size of the pan – small pans yield higher
evaporation rates
Typical Class A Pan 120.7 cm in diameter and 25 cm deep.
a) Potential evapotranspiration estimation
25. Class A evaporation pan.
Pan evaporation generally represent the evaporation
in the edges of large water bodies
Pans may also absorb radiation providing greater
energy for evaporation
Pan evaporation models (which take into account
radiation, wind speed, and relative humidity) have
been developed for interpolation of pan data
Evapotranspiration can be estimated from standard Class-A Pans by multiplying
by a pan coefficient:
𝑃𝐸𝑇 = 𝐾𝑝𝐸𝑝
𝑃𝐸𝑇 = Potential Evapotranspiration
Kp= Pan coefficient
Ep= measured pan evaporation
26. FAO Penman-Monteith Method
The FAO Penman-Monteith method is used to estimate reference
evapotranspiration. The equation is:
𝐸𝑇𝑟𝑒𝑓 =
0.408∆ 𝑅𝑛 − 𝐺 + 𝛾 900
𝑇+273𝑢2 𝑒𝑠−𝑒𝑎
∆ + 𝛾 1 + 0.34𝑢2
ETref = reference evapotranspiration [mm day-1]
Rn = net radiation at the crop surface [MJ m-2 day-1]
T = mean daily air temperature at 2 m height [°C]
u2 = wind speed at 2 m height [m/s]
es = saturation vapour pressure [kPa]
ea = actual vapour pressure [kPa]
es - ea = saturation vapour pressure deficit [kPa]
Δ = slope of vapour pressure curve [kPa°C-1]
Υ = psychometric constant [kPa°C-1]
27. Potential evapotranspiration can be calculated with the Penman-Monteith
equation which is the one step method
The two-step approach is at the present the most popular. It computes the
potential evapotranspiration of the crop from the equation
𝑃𝐸𝑇. = 𝑘𝑐𝐸𝑇𝑟𝑒𝑓
Where kc is a crop factor and ETref is the reference evaporation.
The reference evaporation is often taken as the evaporation of an open water
surface (Eo)
The Netherlands potential evapotranspiration of grass can be estimated from
𝑃𝐸𝑇. = 0.8𝐸0 for summer period,
𝑃𝐸𝑇. = 0.7𝐸0 for winter period
28. where
𝑃𝐸𝑇 = Potential Evapotranspiration (mm/day)
𝑝 = percentage of annual daylight hours (monthly in %)
Tavg=Average of daily maximum and minimum temperatures (monthly in ◦C)
Empirical Methods for Potential Evapotranspiration
Empirical models generally involve the application of linear regression techniques
between evapotranspiration and several climatic variables
Since many climatic variables are interdependent, the most efficient regression
model is the one with the least number of climatic parameters
Blaney-Criddle (1962)
𝑃𝐸𝑇 = 𝑝(0.46𝑇𝑎𝑣𝑔 + 8.13)
29. Turc (1961)
where
𝑃𝐸𝑇 = Potential Evapotranspiration (mm/day)
Tmean = Mean air temperature (daily) (in ◦C)
Rs=Total incoming solar radiation (MJ/m2d)
𝑅𝐻 = Relative humidity (%)
30. Thornthwaite Method
Thornthwaite method is based on the assumption of an exponential relationship
between mean monthly temperature and mean monthly consumptive use.
𝑃𝐸𝑇 = 1.6 Τ
10𝑡 𝐼 𝑎
where
PET = unadjusted PET (cm per month),
t = mean air temperature (°C)
I = annual or seasonal heat index, the summation of 12 values of monthly heat
indices (i) when, 𝑖 = Τ
𝑡 5 1.514
𝑎 = 0.0000006751𝐼3 − 0.000071𝐼2 + 0.017921𝐼 + 0.49239
31. Hargreaves’ Method
Hargreaves based on his work on data from grass lysimeter, proposed the
following relationship to estimate ET,
𝑃𝐸𝑇 = 0.0135 𝑡 + 17.78 𝑅𝑠
where,
PET = reference crop potential consumptive use
t = mean daily temperature (°C)
Rs = incident solar radiation in langlay/day, it can be calculated using the
following relationship
𝑅𝑠 = 0.10𝑅𝑠𝑜𝑆 Τ
1 2
where,
S is the percent possible sunshine hour and Rso is the clear day solar radiation.
32. Turc (1954):
where
𝐸𝑇 = Actual Evapotranspiration (mm/yr)
P = Precipitation (mm/yr)
T =Temperature (oC)
b) Actual evapotranspiration
Coutagne:
33. Soil water budget method
The water balance of the root zone may be written as
𝐼 + 𝑃𝑆 + 𝐺 = 𝐸 + 𝐷 + 𝑄𝑆 + ∆𝑆/∆𝑡
• where I is irrigation, PS is precipitation minus interception, G is groundwater
contribution through capillary rise, E is evapotranspiration, D is percolation from
the root zone to the groundwater system, and QS is surface runoff.
The boundary conditions for applying
the water balance equation are much
better defined with the use of a
lysimeter which is a closed container in
the soil from which the outflow
(drainage) can be measured.
34. Lysimeter
A lysimeter is a measuring device which can be used to measure the amount of actual
evapotranspiration which is released by plants, usually crops or trees.
By recording the amount of precipitation that an area receives and the amount lost
through the soil, the amount of water lost to evapotranspiration can be calculated.
Lysimeters are a tool for water balance studies and solute transport determination.
Lysimeter – a large container holding
soil and plants.