Impact Of Climate Change On Vegetation Phenology In The Arid Regions Of Central Asi

Vegetation phenology can effectively characterize the response of terrestrial ecosystems to climate change.Arid Central Asia is the largest arid region in the temperate zone of the northern hemisphere.It is an area with a fragile global ecological environment and is sensitive to climate change,and it is also an area where current global vegetation phenology research could be stronger.Researching vegetation phenology in arid Central Asia is of great scientific significance for revealing the response mechanism of terrestrial ecosystems to climate change.This study takes the vegetation phenology in arid Central Asia as the research object,based on various data sources such as measured data,remote sensing data,and meteorological data,studies the temporal and spatial variation characteristics and regional differentiation of vegetation phenology in arid Central Asia from 2000 to 2019,and quantifies the effects of temperature,precipitation and extreme climate changes on the vegetation phenology were studied.The simulation and prediction of the grassland phenology in arid Central Asia under climate change were carried out based on the phenology models.In order to reveal the response mechanism of vegetation phenology to climate change in arid Central Asia,and provide new understanding for the interpretation of the non-systematic change mechanism of vegetation phenology under the background of global warming.The main conclusions obtained of this study are as follows:(1)From 2000 to 2019,the start of the growing season(SOS)of vegetation in arid Central Asia was concentrated from mid-February to mid-April.The end of the growing season(EOS)was mainly distributed from early October to mid-December,with the length of the growing season(LOS)duration ranging from 6 to 10 months.In the past 20 years,the SOS showed a trend of delay,with a magnitude of 0.16 days per year,while the EOS advanced at a rate of 0.69 days per year,and the LOS shortened by an average of 0.89 days per year.Vegetation phenology in arid Central Asia has prominent vertical zonal distribution characteristics.For every 1000 meters increase in altitude,the SOS was delayed by 12.4 days,the EOS advanced by 0.4 days,and the LOS shortened by 11.7 days.(2)Temperature and precipitation affect vegetation phenology in arid Central Asia.Overall,the SOS was negatively correlated with temperature and positively correlated with precipitation.In contrast,the EOS and the LOS were positively correlated with temperature and negatively correlated with precipitation in most areas.Different ecological regions are affected differently by climate change.For example,the SOS in the northern steppe region of Central Asia(NSCA)was delayed due to decrease spring temperatures.In contrast,the SOS in the Tianshan Mountains(TSMT)and the Junggar basin desert area(JBDA)was delayed due to increased precipitation.The EOS in the NSCA advanced with decreasing autumn temperatures.At the same time,the EOS was delayed in the JBDA with decreasing precipitation.The LOS basically lengthened with rising temperatures and shortened with increasing precipitation.(3)Most extreme climate indices have increased to varying degrees in arid Central Asia,with the fastest increase observed in the number of warm nights(TN90p)and the fastest decrease in the maximum five-day precipitation amount(RX5day).Extreme climate indices were negatively correlated with the SOS and positively correlated with the EOS and LOS.The highest impact on the SOS was the maximum value of daily minimum temperature(TNx),and other important factors included the mean values of daily maximum temperature(TXmean),daily minimum temperature(TNmean),and warm days(TX90p).The TX90 p had the most significant impact on the EOS and LOS,followed by the cold days(TX10p)and the TXmean.Extreme climates are projected to intensify under different radiative forcing scenarios in the future and will likely continue to affect vegetation phenology in arid Central Asia.(4)The SOS in temperate grasslands and desert grasslands in arid Central Asia has a delayed trend,while mountain meadows showed an advanced trend.Different phenology models had different simulation effects on different grassland types.Models that included drivers of temperature and precipitation performed better.The temperature-precipitation model(TP)had the best simulation effect on temperate grasslands,with a median root mean square error(RMSE)of 4.05 days.The growing degree days model(GDD)had the best simulation effect on desert grasslands,with a median RMSE of 5.37 days.The temperature-precipitation sequential model(TPS)for mountain meadows had the highest accuracy,with a median RMSE of 5.28 days.Three phenological models predict the three grassland types’ SOS under different radiative forcing scenarios,and the SOS for three grassland types shows an advanced trend in 2020-2100,with a more significant trend in high radiation forcing scenarios.