Responses Of Phenology By Climate Change On Pan-Third Pole In The Past Three Decades

The Earth has experienced unprecedented rapid warming in the past 30 years,the Pan—Third Pole region is warming at about twice the global rate.Spring phenology is highly sensitive to climate change,but this phenomenon is rarely reported in this area.Therefore,exploring the spring phenology in the context of severe climate change in the Pan—Third Pole,and the driving factors behind them,are critical to understanding the response and feedback of terrestrial ecosystems in this areaThe development of remote sensing technology makes phenology monitoring probable to Global—scale,and the study of phenology based on satellite data has become a hot topic in ecological study.This study used vegetation index data from three satellites,including GIMMS NDVI,MODIS NDVI,which represents vegetation greenness,and GOME—2 chlorophyll fluorescence(SIF)for photosynthesis of vegetation.Data were taken from the spring vegetation start of season in the Pan—Third Pole region between 1982 and 2015.Subsequently,the following analysis was carried out:1)The reliability of spring phenology in the Pan—Third Pole area was extracted using SIF data;2)The degree and difference between NDVI and SIF affected by snow cover during extraction of spring phenology;3)In the past 30 years,the spring phenology pattern and its changes in the Pan—Third Pole area based on different vegetation index,and 4)The correlation between the spring phenology and climate factors of the Pan—Third Pole area.In summary,this study draws the following conclusions:(1)On the 16 FLUXNET towers of different vegetation types in the study area,the vegetation phenology extracted based on SIF and the FLUXNET GPP have the highest consistency and the strongest correlation(R=0.94,P<0.01),Similar to previous study.(2)Zhang suggested that GIMMS NDVI spring phenology trend due to data quality problems caused by the reduction of NDVI value after 2000.Therefore,the results of the material simulation were verified using MODIS and SIF,and in order to reduce the impact of snow cover on the vegetation index signal.This study uses the average temperature of the five days moving window to determine land surface snow cover.The increase snow cover may result in an underestimation of the trend in vegetation phenology extracted by NDVI,similar to the Wang et al.,2013 result.Excluding the impact of snow cover,the increase in snow cover in the Pan—Third Pole region in 2007—2015 will delay ND VI vegetation by about 0.15± 0.05 days per year,but have little impact on SIF.In additation we also compared Shen et al.,2014;Cong et al.,2013,material it found a more consistent similarity trend and spatial pattern,proving the robustness of the results.(3)During the period 1982—2015,spring phenology in the Pan—Third Pole region mainly began in April—July,with large differences between east and west.In the Alps and the Iranian plateau,spring phenology began earlier(60—100 days),early than Qinghai—Tibet Plateau and Tianshan Mountains(140—180 days).And the start time of the spring phenology is delayed with the altitude rise.In the Alpine,it occurs in about 120—140 days,and in the higher Qinghai—Tibet Plateau,spring phenology begins at 140—180 days and is gradually delayed along the altitude gradient from east to west.(4)Spring phenology in the Pan—Third Pole region showed an early trend during the period 1982—2015,with an average of 0.61±0.2 days.Spatial distribution:The Alps,the western and central part of the Iranian plateau,the eastern part of the Pamir Plateau,the eastern part of the Qinghai—Tibet Plateau,the spring phenology showed a significant range of significant advance.In the western part of the Qinghai-Tibet Plateau,spring weather in the Tianshan Mountains showed a smaller delay in some areas.(5)The increase in pre—season temperatures in the spring of the past 30 years has been a major factor affecting the advance of spring weather in the Pan—Third Pole region(74.6%,mainly in Europe,the Iranian plateau,the Pamir Plateau and the eastern Qinghai—Tibet Plateau.Pre—season precipitation is an important factor affecting arid and semi—arid areas(spatially located in the central and western Qinghai—Tibet Plateau,the southern Tianshan Mountains,the southern Pamir Plateau and the northern Alps).Further research found in the Pan Third.Under the background of extreme warm and humidity,the effect of pre—season precipitation in the Pan—Third Pole region on spring weather showed a significant increase(6)On the regional scale,the pre—season temperature in the Pan—Third Pole region increases by 1?,the spring weather is about 1.3 days ahead,the pre—season precipitation is increased by 10mm,and the spring phenology is about 1.6 days ahead.In arid and extremely arid areas,the SIF spring phenology is the opposite of the NDVI spring phenology response to temperature and precipitation,and in the two arid gradient areas above,the temperature promotes the SIF spring phenology ahead of time.Late NDVI spring phenology,precipitation promotes NDVI spring phenology ahead and delays SIF spring phenology.Through the sensitivity of different vegetation indices in numerical functions,it is found that when the drought index is less than 0.125,that is,in arid and extremely arid environments,the spring vegetation in the Pan—Third Pole area is delayed by the increase of pre—season temperature,and when the drought index is greater than 0.125,the effects of the warming of vegetation spring phenology changed from delay to advance.In extreme and semi—arid conditions,precipitation is important for the advance of vegetation in spring,when the drought index reaches 0.326,warming and increased precipitation contributed to the advance of vegetation spring phenology.Temperatures that are less than this drought gradient are the main drivers of spring weather advance,and an increase in precipitation when the drought index is greater than 0.425 may cause a delay in spring weather.