**5. Summary**

138 Current Issues of Water Management

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Fig. 17. (continued) The radar derived rainfall data from 17 Virtual Rainfall Stations in a 2300 ha Sawah Sempadan Irrigation Compartment produced rainfall distribution pattern which otherwise would always be uniformly distributed since there is only one rain-gauge

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**Rainfall 16 Apr**

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Virtual Rainfall Stn. Tanjung karang Lots In anticipation of future greater competition for irrigation water due to climate change and global warming, paddy water management should be more focused towards water saving and precision irrigation. This book chapter has described new indicators for evaluating the performance of different aspects of an irrigation system for rice cultivation. A GIS-based interactive assessment tool is given using a new concept to characterize the irrigation delivery performance as the season advances. The weakness of a widely used Relative Water Supply (RWS) concept is overcome by using the new indicators, viz. Rice Relative Water Supply (RRWS), Cumulative Rice Relative Water Supply (CRRWS) and Ponding Water Index (PWI). The RRWS can distinctly characterize the oversupply condition for RRWS > 1.0 and undersupply condition for RRWS < 1.0 on irrigation delivery for any given period. A value of 1.0 for RRWS indicates an irrigation delivery that perfectly matches the actual field water demand. A user-interface was developed for structuring the assessment tool within ArcGIS platform. The system can instantly give information on the uniformity of water distribution and the shortfall or excess and what decisions to adopt for the next period. The results are displayed on the computer screen together with colour-coded maps, graphs and tables in a comprehensible form. The system can be adopted as an analytical and operational tool for the irrigation managers to evaluate various water allocation scenarios and water management options.

Water savings can be obtained by practicing precision farming of rice in lowland paddy fields. However a rapid assessment of the paddy soil variability needs to be determined, for example through mapping of the bulk electrical conductivity (ECa) of the paddy fields, so that variable treatments of the management zones can be adopted to save the precious resources. ET monitoring is necessary to determine the required amount of water at each crop growth stage, and the rainfall distribution pattern in the irrigation scheme should be considered to make better use of effective rainfall with respect to the stage of crop development. The practice of precision farming (i.e. applying the right input, at the right place, at the right time, at the right amount and in the right manner using the right tools) will ensure high water and land productivity for a sustainable rice production to feed the growing world population.
