CROPWAT is a decision support tool developed by the Land and Water Development Division of FAO. Its main functions are:

To calculate:

• Reference evapotranspiration
  
• Crop water requirements
  
• Crop irrigation requirements

To develop:

• Irrigation schedules
  
• Scheme water supply

CROPWAT is meant as a practical tool to help agro-meteorologists, agronomists and irrigation engineers to carry out standard calculations for evapotranspiration and crop water requirements, and more specifically the design and management of irrigation schemes. It allows the development of recommendations for improved irrigation practices and the planning of irrigation schedules.

Calculations of crop water requirements and irrigation requirements are carried out with inputs of climatic and crop data. Standard crop data are included in the program and climatic data can be obtained for 144 countries through the CLIMWAT-database. The development of irrigation schedules is based on a daily soil-water balance using various options for water supply and irrigation management conditions. Scheme water supply is calculated according to the cropping pattern provided.
Procedures for calculation of the crop water requirements and irrigation requirements are based on methodologies presented in FAO Irrigation and Drainage Papers No. 24 "Crop water requirements" and No. 33 "Yield response to water".

CROPWAT includes a revised method for estimating reference crop evapotranspiration, adopting the approach of Penman-Monteith as recommended by the FAO Expert Consultation held in May 1990 in Rome. Further details on the methodology are provided in the Irrigation and Drainage Paper No 56.: "Crop Evapotranspiration"

CROPWAT version 5.7, issued in 1992, is written in BASIC and runs in the DOS environment. The program is available in English, French and Spanish, and is distributed as Irrigation and Drainage paper No 46. which includes a manual and guidelines. The manual explains the use of the computer program. The guidelines elaborate on calculation procedures and applications in irrigation planning and management, with examples.
The English version of CROPWAT 5.7 is replaced by CROPWAT version 7.0. The French version of CROPWAT 5.7 can be downloaded from FAO's FTP-server as CRW57-FR.ZIP (293 Kb), the Spanish version can be downloaded as CRW57-SP.ZIP (204 Kb). The program should be unzipped in a suitable directory. The proper directory structure will be restored after running the SETUP command.

The CROPWAT publication can be ordered as FAO Irrigation and Drainage Paper No. 46 through the FAO Sales and Marketing Group (Price US$ 19):

Publications-sales@fao.org

CROPWAT for WINDOWS contains a CROPWAT version in Visual Basic to operate in the Windows environment. It has been developed with the assistance of the International Irrigation & Development Institute (IIDS) of the University of Southampton, UK. The program and the manual in PDF format can be downloaded from FAO's FTP-server as CRW4W3.ZIP and CRW4W-MN.ZIP, respectively. The program should be unzipped in a temporary directory and will be installed with the SETUP command as explained in the included readme.txt file.

A database facility CLIMWAT has been developed which allows a direct link from CROPWAT to an extensive climatic database of 3262 stations of 144 countries worldwide in Asia, Africa, Near East, South Europe, Central and South America. This has been published as FAO Irrigation and Drainage Paper No. 49. For further information and download of the data refer to the concerned CLIMWAT-page.