Abstract Climate change directly affects crop evapotranspiration and irrigation demand. The temporal and spatial variation of crop evapotranspiration is crucial to irrigation schedule planning and water resource management. Using 52 years of climate data from 43 stations in the North China Plain, this study examined trends and spatial distributions of the cotton evapotranspiration (ETc) and irrigation requirement (Iwr) and revealed the impact of climate variation on cotton ETc change. We found that, annual ETc of cotton in the growing season showed a significant declining trend, which decreased from 606 mm yr−1 in 1965-1975 to 551 mm yr−1 in 2006-2016. Annual effective rainfall (Re) and Iwr of cotton’s growing season did not show consistency over the 52 year period, which averaged at 451 mm (441∼ 466 mm) and 122 mm (105 ∼ 145 mm), respectively. The 75% of cotton ETc was supplied by rainfall and 25% by irrigation water. This is much better than for winter wheat where 60% must be supplied by irrigation. The location of the spatial maximum cotton ETc shifted during the past five decades. From 1965 to 1975, maximum ETc values were found in the southern part and then shifted to the northeastern part from 1976 to 1985. During the period of 1986 to 2005, maximum ETc occurred in the middle area and shifted to the western part in 2006-2016. During the past five decades, solar radiation, sunshine hours and wind speed decreased significantly resulting in a significant decrease in ETc at −1.1 mm yr−1. This study highlights the indispensable information of water requirements for future irrigation scheduling of cotton in the North China Plain.

中文翻译：

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1965-2016年气候变化对华北平原棉花需水量的影响

摘要 气候变化直接影响作物蒸散量和灌溉需求。作物蒸散量的时空变化对灌溉计划规划和水资源管理至关重要。本研究利用华北平原 43 个站点 52 年的气候数据，研究了棉花蒸散量 (ETc) 和灌溉需求 (Iwr) 的趋势和空间分布，揭示了气候变化对棉花 ETc 变化的影响。我们发现，棉花生长季的年ETc呈显着下降趋势，从1965-1975年的606 mm yr-1下降到2006-2016年的551 mm yr-1。棉花生长季的年有效降雨量（Re）和 Iwr 在 52 年期间没有表现出一致性，平均分别为 451 毫米（441 ～ 466 毫米）和 122 毫米（105 ～ 145 毫米）。75% 的棉花 ETc 由降雨提供，25% 由灌溉水提供。这比必须通过灌溉供应 60% 的冬小麦要好得多。空间最大棉花 ETc 的位置在过去 50 年间发生了变化。1965-1975年ETc最大值出现在南部，1976-1985年向东北转移。1986-2005年，ETc最大值出现在中部，2006年向西部转移- 2016 年。在过去的 50 年中，太阳辐射、日照时数和风速显着下降，导致 ETc 在 -1.1 mm yr-1 处显着下降。本研究强调了华北平原棉花未来灌溉计划不可或缺的需水信息。