| As global environmental changes and ecological problems become increasingly severe,surface vegetation has become a clear indicator of regional ecological health.Exploring the spatio-temporal coupling relationship between mountain vegetation and climate change has important indicative significance for revealing the impact of climate change on regional vegetation dynamics,monitoring of geographic conditions,and regional ecological protection.Based on the data of 32 meteorological stations in the Qinling Mountains,this paper studies the temporal and spatial changes of temperature and precipitation in the area from 2000 to2018.Combined with the MODIS NDVI data of the same period,studied the spatial distribution characteristics and temporal change trends of vegetation coverage,discussed the influence of Qinling NDVI on climate change.Based on the reconstructed MODIS NDVI data,this article extracts the phenological parameters of the Qinling area,such as the beginning,end,and growing season lengths,and to clarify its key phenological parameter change characteristics and the spatio-temporal response mechanism of phenology to climate change,aiming to provide scientific guidance and theoretical basis for coping with global changes and ensuring national ecological security.The following research results and progress have been mainly achieved:(1)Based on the analysis of meteorological data from 2000 to 2018,it was found that the average annual temperature in the Qinling Mountains increases at a rate of change of0.56?/10 a,The annual average precipitation increased slowly at the rate of 29.03mm/10 a.Among them,the temperature in the four seasons shows a gradual upward trend;the precipitation in the spring and autumn seasons is increasing,and the precipitation in summer and winter decreased;From the perspective of spatial distribution,the geographical spatial distribution of annual average temperature for many years roughly shows a distribution pattern of decreasing temperature with increasing altitude.the spatial distribution of precipitation shows significant differences.Compared with the northern slope,the southern slope has more precipitation,but the precipitation growth trend on the northern slope is greater than that on the southern slope.(2)Based on the analysis of NDVI data,it was found that the vegetation coverage in the Qinling Mountains has in good condition,and the NDVI distribution presents a distribution pattern of "south slope>north slope,west>east,middle>both sides",with significant regional and seasonal differences.The high-value areas are mainly located in the higher altitude areas and eastern regions,and the low-value areas are mainly located in the residential areas such as the southern and northern slopes and foothills.The vegetation growth in summer is the best,and the vegetation coverage in winter is the lowest.On the time scale,the vegetation coverage in the Qinling Mountains has fluctuated and increased at a rate of 2.3%/10 a in the past 19 years.Among them,the average value and rising trend of NDVI on the southern slope are higher than those on the northern slope,but the variation range of the northern slope is larger than that of the southern slope;The NDVI in each season showed an overall upward trend,the spring vegetation cover had the most significant upward trend,with a rate of change of 0.032/10 a,and the summer vegetation has the weakest upward trend,which is0.019/10 a.(3)On the annual scale,the areas where vegetation cover changes are positively correlated with temperature and precipitation account for 20.62% and 67.93% of the total area,respectively.There are certain differences in the correlation between vegetation index and temperature and precipitation.The spatial distribution of vegetation growth and climatic factors coexist with positive correlation and negative correlation,indicating that vegetation growth was jointly affected by the combination of water and heat;On the monthly scale,the NDVI response to climate factors in the Qinling Mountains has a time lag effect.The temperature in May and June is negatively correlated with the temperature of the same period and the cumulative temperature;there is a lag period of 1-6 months for the precipitation of vegetation in the Qinling Mountains.summer precipitation has a positive effect on the growth of surface vegetation.(4)Based on the analysis of remote sensing phenology data,it was found that the initial period of phenology in the Qinling Mountains has concentrated in 60-102 days,the end period of phenology has mainly concentrated in 315-345 days,and the length of the growing season has concentrated in 225-255 days.From a spatial point of view,it has obvious vertical zone distribution characteristics.With increasing altitude,the beginning,end,and growth periods of phenology are delayed,advanced,and shortened,respectively;On the time scale,the beginning of the Qinling phenology growth season showed a trend of advance at a rate of-2.6d/10 a,the end of vegetation phenology was delayed at a rate of 4.3d/10 a,The entire vegetation growth season showed a fluctuating growth trend at a rate of 6.87d/10a;The beginning of the phenology is advanced and the end of the phenology is postponed,and the proportions of pixels in advance and backward are 62.25% and 53.42% respectively;The length of the growing season exhibited a lengthened trend of 59.18%.Among them,the5.12% significantly extended area is mainly located in the middle and high altitude areas of the central and eastern regions;(5)The initial period of vegetation phenology is negatively correlated with the average temperature and precipitation from February to May,accounting for 50.29% and 65.24% of the total area respectively;The end of phenology is mainly positively correlated with the average temperature and monthly precipitation from August to November,accounting for66.63% and 59.77% of the total area respectively;Redundancy analysis(RDA)results show that the vegetation phenology in the Qinling Mountains is affected by both the current season and the previous climatic factors.The degree of response of phenological changes in different aspects to climate change is different.The phenological onset of the north slope of Qinling Mountains was mainly influenced by the temperature in April and the precipitation in December of last year,while the south slope of Qinling Mountains was mainly influenced by the temperature in March-april of that year and the precipitation in November last year.The end of vegetation growth on the northern slope is mainly affected by the temperature from September to October of the year and the precipitation in April,while the southern slope is mainly affected by the temperature from September to October of the year and the precipitation in May of the year. |
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