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

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.