New performance indicators for rice-based irrigation systems

Various indicators are used for evaluating the performance of different aspects of an irrigation system. This study proposes rice relative water supply (RRWS) and cumulative rice relative water supply (CRRWS) indicators to characterize the irrigation water delivery performance as the season advances in rice irrigation systems. These indicators were determined from field tests and evaluated. Traditionally, some standing water depth is kept in the field throughout the irrigation season. Some water is continuously delivered to maintain the standing water depth in the field due to the difference between the maximum standing water depth (WSmaxj) and the present standing water depth (WSj). The widely used relative water supply (RWS) concept is found to incorrectly characterize an oversupply condition on irrigation deliveries for not considering the additional water supply to maintain standing water. Consequently, the cumulative relative water supply (CRWS) gives a wrong scenario in characterizing irrigation delivery performance throughout the season. The RRWS, on the other hand, distinctly characterizes the oversupply and undersupply condition on irrigation delivery as the season advances. A value of 1.0 for RRWS indicates an irrigation delivery that perfectly matches with the field water demand. Both in the main and off-season, RWS remains higher than RRWS during depletion periods (WSj−WSj). On the other hand, the values of RWS and CRWS were higher than RRWS and CRRWS during 3rd to 6th weeks in the main season; and 3rd to 7th weeks in the off-season. The proposed indicators were found to be useful to enhance the decision-making and operational strategy for delivering the right amount of water to the fields for the upcoming period.