evapotranspiration
#1

[attachment=12144]
INTRODUCTION
1.1GENERAL

Evapotranspiration is defined as “the total quantity of water used by the vegetation growth of a given area in transpiration and building of a plant tissue, and that evaporated from the adjacent soil in the area in any specified time.” It therefore includes the water removed from the soil by transpiration and evaporation. Transpiration is the process in which the water that enters the plant roots and is used in building plant tissue finally passes into the atmosphere in the vaporous from through the leaves of the plants. Evaporation is the process in which water from the adjacent soil passes into the atmosphere in the vaporous form. For a given set of conditions, Evapotranspiration obviously depends on the availability of water. If sufficient moisture is always available to completely meet the needs of the plants the resulting Evapotranspiration is called potential Evapotranspiration (PET). Potential Evapotranspiration no longer critically depends on soil and plant factors but depends essentially on climatic factors. The real Evapotranspiration occurring in a specified situation is called actual Evapotranspiration (AET). At the field capacity, since the water supply to the plants is adequate AET will be equal to PET, so that the ratio (AET/PET) is equal to 1. With the reduction in the available moisture (as the soil dries out) the ratio (AET/PET) would be less than unity. The decrease in the ratio (AET/PET) with available moisture depends upon the type of soil and the rate of drying.
1.2 NECESSITY
The crop water need always refers to a crop grown under optimal conditions, i.e. a uniform crop, actively growing, completely shading the ground, free of diseases, and favourable soil conditions (including fertility and water). The crop thus reaches its full production potential under the given environment.
1.3 FACTORS AFFECTING THE EVAPOTRANSPIRATION
The various factors affecting the Evapotranspiration as follows
(1) Evaporation from the soil
(2) Temperature
(3) Wind velocity
(4) Relative humidity of air
(5) Precipitation
(6) Day time hours
(7) Intensity of sunlight
(8) Soil type and topology
(9) Type of crop
(10) Cropping pattern
(11) Length of growing season
(12) Stage of growth of plant
(13) Amount of foliage of plant
(14) Nature of leaves of plant
(15) Method of irrigation
(16) Quantity of irrigation water applied
(17) Quantity of readily available moisture
1.4 OBJECTIVES OF STUDY
The main objective of paper is to choose the best suitable method for the calculation of Evapotranspiration for the study area. In this rankings will be given based on the values obtained by the modified penman method to the values obtained by the other conventional methods.
CHAPTER -2
LITERATURE REVIEW

Empirical method of estimating potential evapotranspiration (PE) has been preferred by several scientists in India to Penman’s (1948) theoretical combination approach, because of the former’s simplicity. However, in view of the doubts expressed in various quarters regarding the applicability of Thornthwaite method, jensan-haise method, Hargreaves method, blaney criddle Method and Hargreaves class A pan evaporation methods for monsoon climates, a comparison is made of the performance of all these methods over different parts of India, using about 26 years of data at 15 stations spread over the country. A large number of more or less empirical methods have been developed over the last 50 years by numerous scientists and specialists worldwide to estimate evapotranspiration from different climatic variables. Relationships were often subject to rigorous local calibrations and proved to have limited global validity. Testing the accuracy of the methods under a new set of conditions is laborious, time-consuming and costly, and yet evapotranspiration data are frequently needed at short notice for project planning or irrigation scheduling design. To meet this need, guidelines were developed and published in the FAO Irrigation and Drainage Paper No. 24 'Crop water requirements'. To accommodate users with different data availability, six methods were presented to calculate the reference crop evapotranspiration (ETo). The Blaney-Criddle, Hargreaves, modified Penman, Thornthwaite, jensan-haise and Hargreaves A pan evaporation methods. The modified Penman method was considered to offer the best results with minimum possible error in relation to a living grass reference crop. It was expected that the pan method would give acceptable estimates, depending on the location of the pan. The blaney criddle was suggested for areas where available climatic data include measured air temperature and sunshine, cloudiness or radiation, but not measured wind speed and air humidity. Finally, the publication proposed the use of the Blaney-Criddle method for areas where available climatic data cover air temperature data only.
CHAPTER -3
VARIOUS METHODS OF EVAPOTRANSPIRATION
INTRODUCTION:

Several researchers have studied the influence of the various climatological parameters on the Evapotranspiration and developed a number of formulae for determining the potential Evapotranspiration. Some of the formulas are purely empirical but some are supported theoretical analysis. The following are some of methods used commonly for determining Evapotranspiration.
• Modified penman method
• Jensen-Haise method
• Hargreaves method
• Thornthwaite method,
• Blaney-criddle method
• Hargreaves class A pan evaporation methods
3.1 MODIFIED PENMAN METHOD:
Based on the concept that Evapotranspiration is intimately connected to incoming solar energy, penman developed a theoretical formula for potential Evapotranspiration which in its modified from is as follows
Et = WRn + (1- W)f(U) (es - eo)
In which
Etp = potential Evapotranspiration for reference crop alfalfa in mm/day;
W = a weighting or weight age factor which is dimensionless:
Rn = net radiation in mm of evaporable water per day;
F(U) = a function of wind velocity;
es = saturation vapour pressure in mbar at the mean daily temperature; and
eo = actual mean vapour pressure of the air in mbar.
Reply

Important Note..!

If you are not satisfied with above reply ,..Please

ASK HERE

So that we will collect data for you and will made reply to the request....OR try below "QUICK REPLY" box to add a reply to this page
Popular Searches: evapotranspiration using matlab, seminar on topic evapotranspiration, code matlab de evapotranspiration,

[-]
Quick Reply
Message
Type your reply to this message here.

Image Verification
Please enter the text contained within the image into the text box below it. This process is used to prevent automated spam bots.
Image Verification
(case insensitive)

Forum Jump: