Technical Performance Assessment of the Subak Heritage Irrigation System in Bali, Indonesia

Subak is a socio-agrarian-religious system of integrated terrace irrigation management on Bali island that involves indigenous peoples and religious aspects in distributing water sources evenly to rice fields. Regardless of its heritage value, Subak irrigation's performance in distributing water for rice is necessary in terms of water scarcity and food production issues. However, there is a limited number of works evaluating the Subak irrigation system's functioning, although it has been present for centuries. This study was conducted to assess the performance of Subak Ulumayu and Subak Sembung in 2018/2019. Several spatial datasets were processed using pySEBAL to generate biomass, evapotranspiration, and transpiration data. Results showed that rice consumed 968-1014 mm of water, which resulting 4.87-4.93 tons rice/ha in this season. Most subfields showed relatively good performance, i.e. Relatively Water Deficit <0.2, adequacy >80%, and equity CV<10%, although the Relatively Yield Deficit was high and efficiency was slightly low. According to those results, both Subak irrigation systems were working satisfactorily to supply water for rice fields among water users. However, there is a remained challenge to optimize rice productivity to contribute to national food security.