| Summary: | Climate change will have a significant effect on crop water requirement (<i>ET<sub>c</sub></i>). The spatial and temporal variations of water requirement of maize under climate change are essential elements when conducting a global water security assessment. In this paper, annual reference crop evapotranspiration (<i>ET</i><sub>0</sub>) and the crop water requirement of maize were calculated by the single crop coefficient method. The crop water surplus deficit index (<i>CWSDI</i>) and coupling degree of <i>ET<sub>c</sub></i> and effective precipitation (<i>P<sub>e</sub></i>) were calculated to analyze the relationship between <i>ET<sub>c</sub></i>, <i>ET</i><sub>0</sub>, and <i>P<sub>e</sub></i>. The result shows that maize average annual <i>ET</i><sub>0</sub>, <i>ET<sub>c</sub></i>, and precipitation were 552.97, 383.05, and 264.97 mm, respectively. Moreover, <i>ET</i><sub>0</sub>, <i>ET<sub>c</sub></i>, and <i>P<sub>e</sub></i> decreased by 3.28, 2.56, and 6.25 mm every decade from 1960 to 2015. The <i>ET<sub>c</sub></i> decreased less than <i>P<sub>e</sub></i> did, which led to the decreasing of both <i>CWSDI</i> and the coupling degree of <i>ET<sub>c</sub></i> and <i>P<sub>e</sub></i>. The tendency of <i>ET</i><sub>0</sub>, <i>ET<sub>c</sub></i> decreased first and then increased, while <i>P<sub>e</sub></i> and <i>CWSDI</i> increased first and then decreased, from west to east of the Heilongjiang Province. In addition, the highest <i>ET</i><sub>0</sub>, <i>ET<sub>c</sub></i>, and lowest <i>CWSDI</i> and <i>P<sub>e</sub></i> were found in the western part of Heilongjiang Province. This study indicated that even though the water deficit in the western region was alleviated and the water deficit in the eastern region grew gradually serious from 1960 to 2015, the drought situation in western Heilongjiang Province should still be taken seriously.
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