SAPWAT 4 is a program for estimating irrigation water requirements of crops, farms and drainage or administrative regions for planning purposes.


SAPWAT  4 is a further development of the SAPWAT 3 and SAPWAT computer programs that is used for estimating irrigation water requirements of crops, farms and bigger areas for the planning and management of crop and area irrigation water requirements. Data is stored for easy reference.

It is based on the FAO 1998 Irrigation and Drainage Paper 56 “Crop Evapotranspiration” by Allen, Pereira, Raes and Smith. It uses the internationally accepted Penman-Monteith approach for calculating reference evapotranspiration, as described by these authors. SAPWAT 4 contains 50 years’ daily weather data for each quaternary drainage region of South Africa, as well as the full set (3262 weather stations) of monthly CLIMWAT weather data (FAO Irrigation and Drainage Paper 49). It is designed as a calculating shell, giving the user full control of data used in irrigation water estimation. Existing data can be added to, edited or reviewed by the user. Multi-year weather data is used to statistically analyse estimated irrigation requirements for different levels of risk. The facility to do enterprise budget analyses is included, as is the facility to do small-scale water harvesting analysis and design. Crop irrigation requirement estimates are used for irrigation system design, as peak requirement and cycle length, two crucial elements in design, can be deduced from the results. Development funding was provided by the Water Research Commission (http://www.wrc.org.za).


Pieter van Heerden

16 Fleur la Grandé

Kolbooi Street


Bloemfontein 9301

Contact : Pieter van Heerden

Email: psvh@mweb.co.za.

Tel: 072 209 9329

Crop irrigation


The SAPWAT 4 program and documentation contained in this website emanate from research projects financed by the Water Research Commission (WRC) and are approved for release. Although every precaution has been taken to ensure that the information is correct, application of results is at the risk of the user.

SAPWAT 4 Copyright © 2016 Water Research Commission

Web Design & Hosting by 1st Web Design