Impacts of extreme temperatures on cotton yields in the context of climate warming: A case study of Xinjiang Provinc

In the context of global warming, extreme temperature events are becoming more frequent. This poses a serious threat to crop production. Cotton is an important cash crop in China, and Xinjiang accounting for 20% of global cotton produced. It is important for the development of Chinese cotton industry to study the effect of extreme temperatures on cotton yield. In this study, we used Mann-Kendall trend test and Sen's slope method to analyse the spatial and temporal characteristics of yield variation, and assessed the response of cotton yield to temperature extremes using the copula function, based on historical climate data and cotton yield data in Xinjiang from 1990 to 2019. The results showed that the upward trend in cotton yield from 1990 to 2019 was highly significant (p < 0.01) in 86% of the areas of Xinjiang. The probability of an increase in cotton production due to extreme temperature effects was greater than 20% in 41.7% of the southern border, but only 26.1% of the northern border. The probability of cotton yield reduction due to extreme temperatures is less than 30% in 92.6% of areas across Xinjiang, and areas with a probability of yield reduction greater than 30% are concentrated north of the Tianshan Mountains. Cotton climatic yield was significantly affected by minimum daily minimum temperature during the cotton growth period and maximum daily maximum temperature for the cotton growth period among the six extreme climate indicators. The probability of a yield reduction of more than 133 kg hm^-2 increased by 16% and the probability of a yield increase of more than 137 kg hm^-2 decreased by 10% as minimum daily minimum temperature during the cotton growth period increased, but increased by 17% and decreased by 12% as maximum daily maximum temperature for the cotton growth period increased. In conclusion, this study demonstrated that cotton production in Xinjiang exhibited an upward trend from 1990 to 2019. The likelihood of cotton yield being negatively impacted rises with increases in minimum daily minimum temperature during the cotton growth period and maximum daily maximum temperature for the cotton growth period. It is beneficial to reduce the risks associated with cotton production, establish production plans, and encourage the growth of the cotton industry's ability to adapt to climate change to clarify how cotton yield occurrence probability responds to extreme climate indicators.