Impact of climate variation from 1965 to 2016 on cotton water requirements in North China Plain.

• Cotton ET c showed a significant declining trend during the past five decades in North China Plain. • Rainfall-crop compatibility index in cotton growing season reached 75% with applied irrigation of 122 mm. • The spatially maximum cotton ET c shifted from southern in 1965-1975 to northeastern then western by 2006-2016. • The decline in solar radiation, sunshine hours and wind speed were responsible for the decline of cotton ET c. 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 (ET c) and irrigation requirement (I wr) and revealed the impact of climate variation on cotton ET c change. We found that, annual ET c 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 (R e) and I wr 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 ET c 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 ET c shifted during the past five decades. From 1965 to 1975, maximum ET c 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 ET c 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 ET c 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. [ABSTRACT FROM AUTHOR]