CROPWAT FAO DOWNLOAD

Some of the series are "broken", but they nevertheless have at least 15 years of data e. Determination of the mean daily percentage of annual daytime hours: The duration of the four growth stages can be estimated with the help of Table 7. The values indicated in the table provide a rough estimate and should only be used if the crop water needs cannot be calculated more accurately due to lack of data. Kc and the climate The climate influences the duration of the total growing period and the various growth stages.

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Kc and the climate The climate influences the duration of the total growing period and the various growth stages.

CHAPTER 3: CROP WATER NEEDS

The lowest values are found when it is cool, humid and cloudy with little or no wind. The crop water need mainly depends on: The K pan is high if: Additionally, effective rainfall is also included calculated and included in the same file. However there are some crops that do not directly fit this model: The relationship between the reference grass crop and the crop actually grown is given by the crop factor, Kc, as shown in the following formula: The Crop Water Model has so far contributed in an efficient utilisation of the available water for crop production, and an effective control of the timing and distribution of water through estimating crop water requirements and preparing irrigation schedules.

These values, however, only refer to the Class A evaporation pan and the Sunken Colorado pan.

Less important is the choice of the various lengths of growth stages. With respect to humidity, data can be provided as relative humidity, dew point temperature or water vapour pressure. Here only the Blaney-Criddle method is given. In general it can be assumed that the growing period for a certain crop is longer when the climate is cool and shorter when the climate is warm.

This method, however, is rather complicated and beyond the cao of this manual. For example, humidity and radiation fal be expressed through different variables. Two files are created for each selected station. As a consequence the ETo and the Kc values do not correspond. The average Kc values are given in Table 9.

Crop Water and Irrigation Requirements Program of FAO (CROPWAT)

Therefore a special coefficient is used K pan to relate one to the other. The duration of the late season stage is 10 and 20 days respectively. For each crop the "minimum" and "maximum" duration of total growing period see also Table 6 have been taken and sub-divided in the various growth stages.

The crop development stage: The crop thus cro;wat its full production potential under the given environment. To determine the crop water need it is best to use an average value of the crop factor Kc. One year after planting, the first harvest takes place, after which the shoots that have produced are removed. The duration of the four growth stages can be estimated with the cropwa of Table 7. In this case it is necessary to decide which variable to use.

For the calculation of the reference crop evapotranspiration ETo, section 3. The late season stage: The sum of the four growth stages should always equal the total growing period. Table 8 indicates per crop the Kc values for each of the four growth stages.

If the sensitivity is low it means that the crop is relatively drought resistant and can withstand water cropwwt fairly well. Kc and the growth stage of the crop A certain crop will use more water once it is fully developed, compared to a crop which has just recently been planted. Cucumber, also fully developed, will use less water than the reference grass crop: For the Sunken Colorado pan, the K pan varies between 0.

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.