Remote Sensing Monitoring Of Hulunbuir Grassland Phenology And The Correlativity Between Phenology And Climatic Factors

Climate change affects the growth of grassland vegetation during different phenological phases.The phenology period of grassland also affects the exchange of moisture and material energy between the surface and the atmosphere.Studying the characteristics of temporal and spatial changes of phenological period and climatic factors of grassland vegetation,exploring the response of climate change to phenological changes,has important scientific significance for achieving optimal management of grazing and revealing the response mechanism of grassland ecosystem to global climate change.In this paper,we used MOD09Q1 data set to extract the phenology period of Hulunbuir grassland vegetation.Through analysis of the spatial and temporal distribution characteristics of vegetation annual phenology period,the temporal and spatial characteristics of climate factors,and the relationship between phenological period and climatic factors,the following conclusions are drawn:(1)The green-up date occurred between April and early June(an average of the 138 th day).The green-up date mainly occurred in the middle or late May,accounting for 74.13% of the total area.The period of occurrence of the brown off date was between September and the end of October(an average of the 277 th day),accounting for a maximum of 36.75% in the latter part of September.The length of the growing season was mainly between 3.5 and 6 months(an average of 136 days),and the maximum between 4 and 4.5 months is 38.07%.Spatially,the green-up date was earlier,the brown off date was late,and the length of the growing season was the longest in the west and north;the green-up date was relatively late,the brown off date was earlier,and the length of the growing season was shorter in the eastern part.Both the green-up date and the brown off date were mainly in advance,and they showed an early trend in 61.2% and 63.83% of the pixels respectively.The length of the growing season was dominated by the prolongation trend,and the proportion of the prolongation trend was 54.95%.The mean green-up date of warm grassland,temperate meadow grassland and lowland meadow were the 98 th,141th and 102 th day respectively,and the average brown off date was the 245 th,279th and 237 th day respectively.The average growing season length was 148,138 and 134 days respectively.The greenup date and the brown off date of the warm grassland and lowland meadow showed a significant advance trend compared with the warm meadow grassland.The green-up date was 43 days and 64 days ahead of schedule in 10 years,and the brown off date was 54 days and 59 days in advance every 10 years respectively.The trend of the length of the growing season was not obvious.The warm meadow grassland and the lowland meadow showed a prolonged trend,while the warm grassland showed a shortening trend,shortening by about 11 days every 10 years.(2)The temperature gradually decreased as the latitude increases in HulunBuir grassland.Precipitation presented a decreasing trend from east to west spatially.The temperature showed a rising trend in the northern part,while the temperature showed a slight decrease or no change in the southern and central parts.Precipitation increased in most areas,concentrated in the central and eastern regions,and there was relatively less precipitation reduction.The temperature showed a decreasing trend in spring,summer and autumn,and the temperature showed a warming trend in winter.The precipitation was mainly an upward trend in spring and summer,while the precipitation was a downward trend in autumn and winter as a whole.(3)There was a positive correlation between the average annual temperature and annual precipitation in the green-up date,and the increase in temperature and precipitation in the lower latitudes delayed the green-up date,while the higher latitude and higher elevation areas promoted the green-up date to advance.The increase of temperature in winter and spring advanced the green-up date.Precipitation in winter will advanced the green-up date,while spring precipitation delayed the green-up date.The effect of average annual rainfall on the brown off date was mainly negative,and the earlier the autumn temperature was,the earlier the vegetation season ended.Spring precipitation had the greatest impact on the brown off date,and spring precipitation advanced the brown off date.The proportion of the length of the growing season was negatively correlated with the annual average,summer and autumn temperatures.The higher the temperature was,the shorter the growing season was,and the spring and winter temperatures showed a promoting effect.The annual precipitation had a negative correlation with the length of the growing season as a whole.Precipitation in spring showed a strong inhibitory effect on vegetation growth,while the autumn precipitation showed a strong promotion effect.