Research On Spatiotemporal Change And The Influence Factors Of Vegetational Returning Green Stage In Northwest Mountainous Area Of China Based On MODIS Data

Vegetation phenology plays an important role in the function of vegetation ecosystem.It has great significance for further research of global climate change and terrestrial ecosystem.The global vegetation phenological change analysis showed that the green period had vegetation in northern latitudes and Tibet Plateau ahead of the trend,but the factors of spatial variation of vegetation greenup mountain areas on the edge of the Tibetan Plateau with the altitude and its influence is a lack of research.To solve this problem,in this study,Minfeng Qiemo County of Heihe basin and the north of Qilian Mountains,the Shiyang River Basin,north of Kunlun Mountains at the junction of the Tianshan Mountains in the oasis,Xinyuan County four mountain area as the study area,using long time series vegetation index based on meteorological station data and terrain data,analysis of vegetation greenup mountain the temporal variation and spatial distribution,revealing the green period changing with altitude variation,factors affecting vegetation green stage extraction,combined with the temperature and precipitation data and on this basis,to reveal the response relationship between meteorological factors and vegetation greenup,reveal the coupling relationship between meteorological factors and vegetation greenup,so that to better understand and simulate the change of ecosystem dynamics of land,for specific problems,solve the ecological management in the protection of ecological fragile service Scientific basis and agricultural and animal husbandry growth provide reference and reference.Through the research and analysis,the conclusions are summarized as follows:?1?different mountain vegetation greenup has different spatial patterns.Heihe River Basin from the southeast to the northwest of the regreening period was delayed,the regreening period mainly concentrated in the upper reaches of the 120-140 day,the regreening period in the middle reaches of the focus on the 90-110 day;gradually postpone the Shiyang River Basin,vegetation greenup entire area from southeast to northwest,green vegetation back in the period of 90-130 days,the late green stage the area is mainly concentrated in the north,and on the 150th day;the obvious spatial distribution pattern of North Tianshan Xinyuan County reviving stage,showing the northwest to the southeast northwest delay trend,green period mainly concentrated in about eightieth days,the southeast is mainly concentrated in about 120th days,and in the 16 consecutive years in the reviving period of spatial distribution the pattern is consistent;at the junction of the Kunlun Mountains North Minfeng Qiemo county and oasis vegetation greenup showed the regreening northern South is early,and the proportion of non vegetation Larger.In general,different vegetation greenup in different regions has different spatial patterns.?2?The vegetation change fluctuated trend of green period.The upper reaches of the Heihe River Basin has 2001-2016 years of vegetation greenup ahead of the trend,ahead of the rate of 0.46 d·a^-1 in the naturalvegetation turning green date back2001-2016 years trend rate of reviving stage was 0.53 d·a^-1 after 2001-2016 years of vegetation in Shiyang River Basin;early reviving period trend,ahead of the amplitude of 0.03 d·a^-1Xinyuan County,north of the Tianshan Mountains;vegetation green 2001-2016 years reviving period have advance ahead of the trend,the amplitude of 0.64 d·a^-1;2001-2016 Kunlun mountain mountain vegetation greenup has the tendency to postpone,delay rate of 0.41 d·a^-1.?3?The study area vegetation green period with the change of altitude changes are nonlinear,is a complex process of change,reviving period with the change of altitude there is a flip down"S"type:in a range of altitude,with the increase of altitude,the vegetation greenup showed a significant delay trend.With the altitude rising,reaching a certain altitude after reviving stage gradual change in trend,when the altitude continues to rise to a certain height,and significantly delayed reviving period trend,and consistency of the four research area has a higher trend showed a down turn,"S"type.Overall,the mountain vegetation green stage increased with elevation of the terrain factor gradually delayed phenomenon.?4?The time resolution of the regreening period remote sensing data extraction accuracy.The analysis results show that the extraction of vegetation greenup with different spatial resolution data,the results from small differences in the regreening period differences extracted by different time resolution data greatly.Thus we can conclude that the factors affecting vegetation greenup in Heihe basin is mainly extracted time resolution,different time resolution extraction results.?5?The relationship between vegetation and climate factors in green stage.Heihe vegetation greenup is mainly controlled by temperature.NDVI and temperature in Heihe watershed vegetation has obvious lag relationship between the upstream temperature and vegetation NDVI lag days in 80¹10 days,middle temperature and vegetation NDVI lag days in 50⁸2 days;upstream precipitation and vegetation NDVI lag days in 20-50 days,in the middle there is no NDVI and precipitation lag relationship.