online_blaney_criddle: Potential evapotranspiration by the Blaney-Criddle method. Formulas. p = f(m,L,H) f = p(t + ) · a,b = f(i,RH,w) [ET]o = a + bf. The estimation of potential evapotranspiration is achieved by adopting empirical approaches, such as the Thornthwaite equation, the Blaney-Criddle formula. Notes: Evapotranspiration was calculated using a modified Blaney-Criddle method. Average effective rainfall is the amount that is useful to crops in an average.

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The comparisons show that the published estimates are slightly closer to the measured values than estimates obtained using the SCS Blaney- Criddle modification as given in Table Exact values of the input parameters are not required.

An average value is to be used with a medium total growing period. For the Class A evaporation pan, the K pan varies between 0. The Kohler- Nordenson-Fox method was shown to give the overall best results in predicting pan evaporation. Calculations of water use rates are normally obtained from estimates based on climatological and field data. This selection process is, admittedly, rather arbitrary and may be dependent as much upon personal experience as scientific criteria.

Blaney–Criddle equation

Model Calibrations Results shown in the previous section indicate the need for calibration of the various evapotranspiration formulas. In other words, it is the amount of water needed by the various crops to grow optimally. Compare, for example, green beans with dry beans Table 7. All measurements, except those taken to measure actual water use, were taken from lysimeters which were surface irrigated and had water tables.


ETo is the rate of evapotranspiration from a large area, covered by green grass, 8 to 15 cm tall, which grows actively, completely shades the ground and which is not short of water see Fig. Although improving the mefhod basis of the models, the crop and soil parameters are usually fairly difficult to define.

Blaney Criddle & Hargreaves method of Measurement of Evapotranspiration

When a crop is harvested “green” or “fresh” the late season stage is short. Table 4 is used. This page was last edited on 30 Marchat Actual evapotranspiration is the rate of ET that crivdle in the field under limited soil moisture conditions and other factors.

Email The subscriber’s email address. Table 14 gives for each crop a minimum and a maximum value for the crop water need.

Blaney–Criddle equation – Wikipedia

Simpler Hydrometeorological equations cgiddle to be used where obtaining such data is impractical, to give comparable results within specific contexts, e. An advantage of using clipped grass as opposed to alfalfa is that it is cridcle necessary to apply crop coefficients to the reference crop to indicate its growth stage.

Sometimes, depending on local practices, a virgin crop is followed by 2 or 3 ratoon crops. For the Green River Basin, four types of water use rates were available during the study period.


As a consequence the ETo and the Kc values do not correspond. Most are adjustments of the coefficients in the wind term, although more extensive modifications have also been presented e. It should be kept in mind that the influence of variations in the total growing period on the crop water need is very important. The duration of the four growth stages can be estimated with the help of Table 7.

The Kc values are rounded to the nearest 0. Of course the water in the blaey and the grass do not react in exactly the same way to the climate. The Blaney—Criddle equation is a relatively simplistic method for calculating evapotranspiration.

Rice For paddy rice the values indicated in Table 11 should be used.

Table 8 indicates per crop the Kc values for each of the four growth stages. Cahn Archard equation Materials science John F. These applications, however, are usually more the modification of the methodology of application of the models than modification of the actual models.

Pan Evaporation Method 3.