Vegetation Phenology And Its Response To Climate Change Based On MODIS Vegetation Index In Three-River Headwater Region

The Study on vegetation phenology changes in the Three-River Headwater Region(TRHR)and its response to climate change,which has important practical significance,for understanding the formation mechanism of grassland productivity and its future trend,and the quantity of livestock in grassland animal husbandry structure optimization so as to realize the sustainable utilization of grassland resources,establishing regional land management policy.Based on the the data of meteorological stations to analysis the changes of the average annual temperature and precipitation from 1960 to 2014 in the TRHR,Spatial interpolating of data from 2000 to 2014,to analyse the climate change in the TRHR since twenty-first Century;Based on 250 m 8d MODIS NDVI data set,we use the S-G filtering method to reconstruct NDVI time series and analyse the regional NDVI change from 2000 to 2014;Then,we extract the phenological information by using TIMESAT software,analysing the temporal and spatial changes of vegetation phenology and its response to climate change.The main conclusions are summarized below:(1)The three statistical indexs of NDVI showed increased in different degrees from 2000 to 2014.In recent years,the vegetation in the TRHR has changed,the fragile ecological environment gradually improved;In space,NDVI is gradually decreasing from southeast to northwest.(2)In the past 55 years,the annual average temperature presented upward trend.Especially since twenty-first Century,warming trend is obvious in the TRHR,indicating that the impact of global warming on TRHR increased.Annual precipitation in the TRHR were increased,but the increasing trend was not significant.In space,the annual average temperature and annual precipitation decreased from the southeast to the northwest,as a whole,the climate change in the TRHR showed the trend of warming and humiding.(3)The start of the vegetation growing season(SOS)in the TRHR begining in the 125-155 day of the year,280-290 day of the year in the end of the growing season(EOS),the length of the growing season(LOS)concentrated on 130-160 days;From 2000 to 2014,the SOS showed an advancing trend,but the EOS showed no significant changes,so the LOS as a result of the earlier SOS of the overall extension;In the spatial distribution,The SOS delayed from the southeast to the northwest,and the EOS gradually advanced from the southeast to the northwest,and the LOS gradually shortened from the southeast to the northwest.The trend of inter annual variation of SOS in the space generally weakened from the southeast to the northwest.(4)Considering the influence of altitude factors,there are three important dividing lines of 3000 m,4000m and 4200 m on the altitudinal gradient of vegetation NDVI and annual precipitation.The area below 3200 m in elevation,SOS with the altitude rising rapidly delayed,while higher than 3200 m,SOS changes smoothly.The dividing line beginning the variation trend of growth of 3000 m,3900m and 5300 m in the altitude distribution.The effects of temperature and precipitation on the SOS are different at different altitudes,and the precipitation is the dominant position under 4400 m,and the temperature above 4400 m is dominant.(5)The winter precipitation has great influence on advancing of SOS,more winter rainfall or snow is conducive to SOS advance;Spring precipitation and temperature affected the SOS,especially about 30 days of the preseason's precipitation and 25 days of the preseason's the temperature.