LAUSR

Most of the paddy rice in the Sanjiang Plain is irrigated with groundwater. In recent years the water requirement has been increasing with the rapid spread of paddy fields, while the groundwater table is constantly falling. In order to maintain the sustainable development of water resources in the long term, comprehensive measures, including conjunctive use of surface and groundwater and water‐saving practices, should be jointly applied. To investigate these comprehensive measures, a study on the conjunctive use of groundwater and surface water for paddy rice irrigation has been ongoing since 2014. This paper presents water management scenarios based on the study by adopting various water‐saving irrigation technologies and measures, volume of reused water, and application of groundwater and surface water. A semi‐distributed water balance model was developed to simulate the water cycle at irrigation district level in order to analyse water productivity and groundwater dynamic response to various scenarios. Based on this study, reasonable water use modes under different hydrological years are proposed. These modes show how and when to use groundwater, surface water and return flow. Groundwater and surface water should be conjunctively used with groundwater as the main source for irrigation, surface water as an auxiliary source and reused water as a supplementary source. © 2020 John Wiley & Sons, Ltd.