Multi-scale Change Of Climate And Its Relationship With NDVI In Qinling Area

Climate change has the characteristics of non-linear and non-stationary fluctuations,and there are periodic changes at various scales.Climate change affects the succession of vegetation,and vegetation is an indicator of regional climate change.Discussing the periodic differences and spatial changes of climate change in Qinling area from different time scales,and analyzing the multi-scale response of regional Normalized Difference Vegetation Index to climate change are of great significance to the prediction of the regional climate system and the protection of regional ecological environment.Based on the temperature and precipitation data of 30 meteorological stations in Qinling area from 1959 to 2018,this paper analyzes the multi-scale periodic characteristics of the time series of climate change on the north and south slopes of Qinling Mountains through the EEMD method,wavelet analysis,power spectrum analysis and other methods.Analyze the spatial distribution changes and discuss the response of temperature and precipitation to the climate index at different time scales.In addition,the temperature data of 28 meteorological stations in the Qinling area reconstructed by the tree-ring width chronology extended the study period,and the temperature was studied through EEMD method and TDIC method,with a view to better inter-decadal and understand the multi-scale periodic characteristics of the temperature in the long-term series of Qinling Mountains above the century scale.Taibai Mountain,as the main peak of Qinling Mountains,has a typical vegetation response to climate change in Qinling Mountains.In this paper,the 172-year NDVI in July reconstructed from the treering width chronology in the Taibai Mountain area of Qinling Mountain is selected to analyze the variation characteristics of NDVI on different time scales and its multi-scale response to climate factors.The specific results are as follows:(1)During the past 60 years,the overall temperature of Qinling Mountains showed a significant non-linear upward trend,and the north slope increased faster than the south slope.The temperature on the north and south slopes of Qinling Mountain has periodic oscillations on multiple time scales,both interannual and interdecadal.On the interannual scale,the northern slope has quasi-3-4a and quasi-7a,the southern slope has quasi-3-4a and quasi-8a periodic oscillations;the inter-decadal scale on the northern slope has quasi-17-22 a,quasi-45 a,and the southern slope Quasi 16-23 a,quasi 45 a periodic oscillation.The temperature on the north and south slopes has periodic changes with similar scales,but the start and end years and amplitudes differ on different time scales.The trend term shows that the temperature in Qinling Mountain has a trend of first falling and then rising within 60 years.The non-linear rising trend is the main form of temperature fluctuation in Qinling area.The response of Qinling area temperature to the climate index is different on different time scales,and it shows differences on the north and south slopes.In terms of spatial changes,the overall temperature of Qinling Mountains has been increasing,and the temperature-increasing area has spread from northwest to southeast.The trend of temperature changes in different regions of Qinling area is different,and the transition time of changes is also different.The temperature changes in the entire study area are not completely synchronized.(2)During the past 60 years,the precipitation in the Qinling area showed an insignificant non-linear downward trend,and the decline rate of the northern slope was faster than that of the southern slope.The precipitation on the north and south slopes of the Qinling Mountains has periodic oscillations on multiple time scales,both interannual and interdecadal.On the interannual scale,the northern slope has quasi-3a and quasi-7a,the southern slope has quasi-3a and quasi-6-7a periodic oscillations;the interdecadal scale has the quasi-12 a and quasi-25 a on the northern slope,and the quasi-20 a and quasi-20 on the southern slope-40 a periodic oscillation.The trend term shows that the precipitation on the north slope shows a downward trend throughout the study period,and the precipitation on the south slope shows a trend of first decreasing and then slightly increasing.The quasi-3a scale fluctuation of precipitation is the main variation of precipitation in Qinling area.The precipitation on the north and south slopes of the Qinling Mountains responds differently to the climate index at different time scales.Spatial changes reflect a downward trend in precipitation in most areas over the past 60 years.Since the beginning of this century,the downward trend of precipitation has continuously expanded to the west and south,but the rate of decline has gradually decreased.At the end of the study period,compared with the previous period,the decline range on the north slope slightly decreased;the decline range on the south slope expanded slightly.(3)During the past 179 years,the temperature of the north and south slopes of Qinling Mountain showed a non-linear increasing trend in early spring,and the temperature fluctuation range of the north slope was generally larger than that of the south slope.The temperature on the north and south slopes has significant characteristics of different time scales.The north slope has quasi 3a,quasi 6a,quasi 18 a,quasi 42 a,quasi 80-100 a,and the south slope has quasi 3a,quasi 7a,quasi 19 a,quasi 37 a,quasi 70-100 a The average period.The temperature change in the early spring of the northern slope of the Qinling Mountains plays a decisive role in the interannual scale change,followed by the interdecadal period and the weakest in the quasi-century;the interannual scale on the southern slope is the most significant,followed by the quasi-century change and the lowest interdecadal change.The early spring temperature in Qinling Mountain has a significant correlation with the AMO in the same period,and there is a significant correlation with the SOI,NINO3.4,NP,and December NAO in May.On the inter-annual scale,the response to the May sea temperature in the NINO3.4 area is the most significant;on the inter-decadal scale,the response to the AMO is the most significant;on the quasi-century scale,the temperature response to each index is significant.(4)The NDVI temporal change characteristics of Taibai Mountain in July show that in the past 172 years,both the north and south slopes showed a weak non-linear upward trend,and there was no abrupt change point.On the northern and southern slopes,July NDVI has an average period of 3.3a,8.1a,and 3.5a,8.8a on the interannual scale;and an average period of 18 a,36a,and 64.8a on the decadal scale.The average period of 19.1a,34.4a and 68.8a.The main factor that responds better to NDVI on the interannual scale is precipitation,and the main factor that responds better to the NDV on the interdecadal scale is temperature.In addition,NDVI is significantly negatively correlated with spring cloud cover,is significantly negatively correlated with spring water vapor pressure,and performs differently on the north and south slopes.It shows that the NDVI of Taibai Mountain in July is comprehensively influenced by heat factors such as air temperature and cloud amount,and moisture factors such as precipitation and water vapor pressure,and shows a difference between the north and south slopes.