Effect Of Meteorological Drought And Extreme High Temperature On Cotton Yield In Central Asia

With the increase of global warming,the magnitude,duration,and frequency of extreme climate events,including drought,heatwave and heavy rainfall,increase continuously and will consequently cause a significant increase and aggravation of agrometeorological disasters.Uzbekistan is an agricultural country,located in the interior of Central Asia,with complex climatic conditions,high variability of meteorological elements such as precipitation and temperature,frequent occurrence of extreme weather events,and serious threats to crop yields.Therefore,in the context of global warming,it is important to carry out research on meteorological drought and extreme heat on cotton yield in Central Asia.In this study,we reviewed the development of the APSIM-Cotton model from the computer management system SIRATAC to the APSIM-Cotton model which is widely used,and analyzed the advantages and disadvantages of each stage of the model development.The applications of APSIM-Cotton are compared under different management measures and the use of the APSIM-Cotton model is extended to the Tashkent region of Uzbekistan.The APSIM-Cotton model was calibrated and validated at Zangiata experimental station in the Tashkent region of Uzbekistan by using filed experimental data.Based on the CMIP6 climate change datasets for three shared socio-economic pathways（SSP1-2.6,SSP3-7.0 and SSP5-8.5）,we analyzed the SPEI in three-month steps（SPEI-3）to characterize the arid-humid fluctuations within the cotton seasons from 2021 to 2090,and simulated the changes of cotton yield in meteorological drought and high temperature event considering the CO₂fertilization.The main conclusions are as follows:（1）The APSIM-Cotton model has relatively well simulation capability in arid and semi-arid regions,and is especially suitable for simulating yield changes and economic risks under extreme climatic circumstances.The calibration and validation of the model revealed that the model can better simulate the impact of climate fluctuation and climate change on cotton production in Tashkent region.（2）During the cotton growing period of 2021-2090,the temperature and precipitation in Tashkent show a significant increase compared to 1961-1990 under three emission scenarios,SSP1-2.6,SSP3-7.0 and SSP5-8.5.（3）The fertilizing effect of CO₂could increase yield by 14.9%to 25.0%.The fertilizing effect of CO₂varies among emission scenarios and there is a potential risk that high temperatures during the cotton reproductive period will weaken the fertilizing effect of CO₂under future scenarios with high radiative forcing,and the contribution of CO₂will not increase continuously when the concentration reaches 750μmol/mol or more.（4）There is a significant trend of drought in the cotton reproductive period under the three future emission scenarios of SSP1-2.6,SSP3-7.0 and SSP5-8.5.The probabilities of severe drought events in the future under the three emission scenarios increased to 20.0%,36.7%and 40.0%in 2035,resulting in 28.0%,29.6%and 32.1%decrease in cotton yield compared with the historical period,respectively.The probability of a severe drought event increases to 46.7%,100%and 100%,respectively,in the 2075 time period;resulting in a decrease in cotton production of 31.5%,33.1%and 35.7%,respectively.Under the SSP3-7.0and SSP5-8.5 scenarios,the probability of extreme drought events in the 2075 time period is66.7%and 86.7%,respectively,resulting in yield decreases of 41.3%and 54.2%,compared to the historical period.（5）The frequency of extreme high temperature events will increase significantly in the future under the SSP1-2.6,SSP3-7.0 and SSP5-8.5 scenarios compared with the historical period,which will correspondingly lead to shorter cotton growing period and lower yield.In2035,the extreme high temperature thresholds under different SSP emission scenarios are37.8℃,38.1℃and 38.3℃,the probability of extreme high temperature events increases to13.3%,10.0%and 16.7%respectively,and the cotton yield in extreme high temperature years decreases by 28.9%,37.7%and 35.4%respectively compared to the historical period;in 2075,the extreme high temperature thresholds are 38.2℃,40.7℃and 42.0℃,the probability of extreme high temperature events increased to 20.0%,20.0%and 40.0%,respectively,and the cotton yield in extreme high temperature years decreased by 33.0%,55.2%and 70.0%,compared with the historical period,respectively.In addition,Controlling high temperatures within the cotton growing season can effectively reduce the yield damage caused by climate change.The contribution was 16.6%and 38.6%when the maximum daily temperature was controlled to below 38°C.The contribution rates were 2.7%and 12.4%when the temperature was controlled below 40°C.Meteorological drought and extreme high temperatures are the main stress factors affecting crop yield,therefore,in the context of global warming,research on meteorological drought and extreme high temperatures on cotton yield in Central Asia will help to understand the development prospects of the cotton industry in Central Asia,scientifically predict the potential for cooperation between China and Central Asia,and provide a foundation for developing mitigation strategies.