Temporal And Spatial Variation Characteristics Of Vegetation Phenology And Its Response To Climate Factors In Northeast Asia

Vegetation phenology is an important indicator of climate and natural environmental changes,and its changes are more prominent in the context of global climate change.At present,relevant studies have shown that the temporal and spatial changes of different vegetation types in phenological periods are quite different,and their response to climate change has also become a key issue of current concern.In the past long period of time,global temperature rise has become a reality,but in recent years,studies have shown that due to the El Ni?o phenomenon in 1997-1998,the global surface temperature has entered a "interrupted" period from a rapid warming period.In order to study the spatiotemporal characteristics of the phenological changes of different vegetation types in Northeast Asia and their response to climate change under the conditions of such climate change,this study selected 1998 as the boundary,based on the northern hemisphere GIMMS NDVI3 g data set extracted by five methods The average value of the phenological period of the phenology is calculated,and the Start of Growing Season(SOS)and End of Growing Season(End of Growing Season,EOS)and Length of Growing season(GSL)three phenological data to analyze the trend of vegetation phenology and its response to climate change,the results show:(1)Vegetation phenology periods in Northeast Asia all show certain zonal distribution characteristics.The greening period is gradually delayed from south to north,concentrated on the 110 th to 130 th day,and the yellowing period shows a trend of early fluctuations concentrated on the 275-300 th day,and the length of the growing season varies from day to day.It gradually shortens from south to north and lasts between 150-200 days.Among different vegetation types,broad-leaved forests have the earliest greening period and grassland the latest;grasslands have the earliest yellowing period and broad-leaved forests are the latest;the length of the growing season is the shortest grassland and the longest is broad-leaved forest.(2)In terms of time,in the pre-warming period,the turning green period of the five vegetation types in Northeast Asia all showed a trend of advancement,the advancement rate of broad-leaved forest was the highest(0.39days/year),and the yellowing period of the five vegetation types all showed a trend of delay.However,during the intermittent warming period,all vegetation types have slowed down their greening period.Coniferous forests,mixed forests and grasslands are all early in the yellowing period,and coniferous forests(0.78days/year)and mixed forests(0.44days/year)are significantly earlier.Spatially,the vegetation types that showed an early trend of turning green before the warming interruption were cultivated land and forest,with a pixel ratio of 76%,and only 24% of the pixels showed a postponement trend,mainly forest vegetation types;58.4% of the vegetation types in the dry yellow period Pixels showed a postponement trend,mainly coniferous forest vegetation types,41.6% of the pixels showed an early trend,mainly broad-leaved forest and cultivated land vegetation types.During the intermittent warming period,the proportion of pixels in the early green period decreased by 10.1%,and the proportion of delayed pixels increased by 10.1%,mainly in coniferous forest vegetation types;the proportion of pixels in the late yellow period decreased by 5.9%,which was earlier The proportion of pixels increased by 5.9%,and the vegetation type is still dominated by coniferous forests.(3)During the period from 1982 to 2014,the greening period of vegetation in Northeast Asia had the most obvious response to the preseason temperature.At the same time,the greening period of the five vegetation types had a significant negative correlation with the preseason temperature,that is,the increase of preseason temperature made the greening period earlier.The correlation between vegetation yellowing period and preseason climatic factors is spatially heterogeneous.It is roughly bounded by 55°N,and the increase in preseason temperature and precipitation in the northern region advances the vegetation yellowing period.Coniferous forest vegetation types are the main types;the preseason temperature increase and precipitation increase in the southern region delay the yellowing period of vegetation,and the vegetation types are mainly broad-leaved forests,mixed forests,grasslands and arable land.The results of the pre-warming interval are the same as the whole time period.During the warming interval,the preseason temperature is still the main controlling factor for the vegetation turning green period.Its impact on forest vegetation becomes stronger,and its impact on cultivated land and grassland becomes weaker,and the entire region is significant The level of sex decline;the yellowing period of coniferous forests and grasslands has a negative partial correlation with preseason precipitation,the yellowing period of mixed forests and cultivated land has a negative partial correlation with preseason temperature,and the yellowing period of broad-leaved forests changes from precipitation dominance to cloud coverage.The dominant positive partial correlation,the yellowing period is still affected by many factors,but the result is not significant.(4)In the pre-warming period,the greening period of the five planting types were all advanced,and the temperature sensitivity in descending order was broad-leaved forest(3.1day/?),cultivated land(2.8day/?),and mixed forest(2.3day/?).,Grassland(1.5day/?),coniferous forest(1.4day/?);the yellowing period of the five planting types is postponed,and the sensitivity degree from large to small is coniferous forest(2day/?),broad-leaved forest(1.6day/?),cultivated land(1.4day/?),mixed forest(0.9day/?),grassland(0.8day/?).However,during the intermittent warming period,the temperature sensitivity of the five plantings during the re-greening period showed that the advancement of the re-greening period of the mixed forest increased by 9% compared with the previous period of the warming interruption,while the grassland decreased by 73%,the cultivated land decreased by71%,and the broad-leaved forest decreased by 32%,Coniferous forests are reduced by 7%;the yellowing period of five planting types is advanced,and the advancement of mixed forest is 4.5 times of the previous period of intermittent warming,cultivated land is 3 times,grassland is 1.9 times,coniferous forest is 1.8 times,and broad-leaved forest is 1.8 times.1.6 times.It can be seen that during the intermittent warming period in Northeast Asia,the vegetation phenology period is indeed different from previous studies,and the yellowing period changes most obviously.The sensitivity to precipitation during the re-greening period increases during the intermittent warming period.The change in the degree of precipitation sensitivity during the re-greening period is grassland(-0.7day/mm),coniferous forest and mixed forest(0.5day/mm).,Arable land(-0.3day/mm),broad-leaved forest(0.22day/mm);the sensitivity to precipitation in the dry season is still relatively small.During the intermittent warming period,the vegetation yellowing period is sensitive to cloud coverage.The yellowing period of broad-leaved forest,grassland and cultivated land is delayed by0.5day/%,0.2day/% and 0.2day/%,respectively.The yellowing period of coniferous forest is delayed.0.3day/% in advance,the mixed forest did not change much.