High ambient air and water temperatures can cause high-temperature damage to ripening rice grains after rice heading and has recently become a major issue of concern. Spill-over irrigation (also referred to as continuous irrigation with running water) is an effective countermeasure that involves simultaneous irrigation and drainage to reduce the ponded water temperature in paddy fields. However, it is necessary to understand the impact of this technique on downstream water temperatures. In this study, the discharge and water temperature variations in a dual-purpose canal (also referred to as irrigation-cum-drainage canal) were measured along the main canal of the Tedori-gawa Shichika canal system in Japan. The discharge and water temperature variations in a branch drainage canal were also monitored to analyse the influence of the return flow on the water temperature in the main canal. Based on these observations, a new numerical model was developed to simulate the water temperature variations in the main canal considering meteorological conditions, heat transfer of water in the open canal, and return flow from upstream paddy fields. Finally, the model was applied to examine possible global warming scenarios and discuss the effectiveness of paddy water management in mitigating high-temperature damage in downstream paddy fields.

中文翻译：

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考虑上游稻田回流的两用渠道水温变化模拟模型

高环境空气和水温会对水稻抽穗后成熟的稻谷造成高温损害，最近已成为人们关注的主要问题。溢灌（也称为流水连续灌溉）是一种有效的对策，涉及同时灌溉和排水，以降低稻田积水温度。然而，有必要了解这种技术对下游水温的影响。在这项研究中，沿日本手取川 Shichika 运河系统的主要运河测量了两用运河（也称为灌溉兼排水运河）的流量和水温变化。还监测了支流渠的流量和水温变化，以分析回流对干渠水温的影响。基于这些观测，开发了一个新的数值模型来模拟考虑气象条件、明渠中水的传热和上游稻田回流的干渠水温变化。最后，该模型用于检查可能的全球变暖情景，并讨论稻田水管理在减轻下游稻田高温损害方面的有效性。明渠中水的传热和上游稻田的回流。最后，该模型用于检查可能的全球变暖情景，并讨论稻田水管理在减轻下游稻田高温损害方面的有效性。明渠中水的传热和上游稻田的回流。最后，该模型用于检查可能的全球变暖情景，并讨论稻田水管理在减轻下游稻田高温损害方面的有效性。