Improvement of SAPWAT as an irrigation planning tool

[摘要] English: In a world with a continuous reduction in per capita availability of fresh water, the increasein the efficiency of irrigation water use becomes more important as a means to postpone thetime when water shortages will restrict crop production. Irrigation uses 62% of SouthAfrica's fresh water resources; therefore a saving in irrigation water through an increase inefficiency could have a large impact on total water use. Informed irrigation requirementplanning is one way in which irrigation water use efficiency could be increased.Associated to efficient irrigation water use, is the effective use of irrigation soil as a resource.Problems such as waterlogging and salinity are found on 19% of irrigated soil in SouthAfrica. Increasing the efficiency of irrigation water use could reduce the rate of increase ofthese problems and it might even decrease the occurrence.With the eye on the efficient planning of irrigation areas, research in crop irrigation waterrequirements has been done over time. Various approaches and planning aids have beendeveloped for the estimation of irrigation requirements. During the second half of the 20thcentury products like the FAO's CROPWAT and the South African SAPWAT weredeveloped. Both these programs had shortcomings which made their use somewhat difficult.Development of SAPWAT3 followed with the objective to develop a user-friendly programthat could be used as widely as possible.The estimation of irrigation water requirements by SAPWAT3 is based on the internationallyaccepted Penman-Monteith approach. The former links the climate data of a specific weatherstation with crop characteristics to determine a water requirement for a specified place andtime.The growth and development of crops are influenced by temperature; therefore the cropgrowth characteristics have been linked to the Köppen climate system as a means of growthand development periods for warm and cool areas. About 5 100 weather stations in 144countries with either daily or monthly values are included in SAPWAT3. A large number ofcrops are also included in the data files. If enough daily climate data are included, SAPWAT3 does consecutive year-on-yearirrigation requirement calculations, which are then used to determine different levels of nonexceedanceof the irrigation requirement. This enables the designer of systems or the wateruse planners to plan for different levels of risk.A linkage between enterprise budgets and estimated irrigation requirements is also built intoSAPWAT3. This enables the user to plan crop combinations which will provide a potentialincome while also considering water supply constraints.The crop growth characteristics included in SAPWAT3 and in similar programs, are the weakpoint of such programs because they are based on calendar time and not on thermal time. Acomputerised methodology has been developed that uses measured crop water requirementsand temperature data to link crop growth and development to thermal time. Thismethodology will be included as a module in the next version of SAPWAT3.SAPWAT was accepted by the South African irrigation fraternity. To determine why thiswas so, and to determine future upgrade approaches that need to be considered, the level ofadoption of SAPWAT was investigated. Good and bad points about SAPWAT which hadbeen identified through verbal feed-back from users were kept in mind and confirmed duringthe development of SAPWAT3. The feedback on SAPWAT indicated the need to improvethe functionality of SAPWAT as an irrigation planning tool, to evaluate and to verify itsoutput and to test its potential for adoption by users. The feedback also indicated thatSAPWAT3 is easy to use and that it gives credible results, two aspects that enhance adoption.Therefore it can be expected that future improved versions will also be well received,acceptable and used by the irrigation planning community.

[发布机构] University of the Free State