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Characteristics Of Climate Change In Spring And Their Response Sensitivities Of Vegetation In The Qinling Mountains

Posted on:2021-03-12Degree:MasterType:Thesis
Country:ChinaCandidate:G Z QiFull Text:PDF
GTID:2370330611457036Subject:Environmental Science
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The response of terrestrial ecosystems to global climate change has obvious regional differences and spatiotemporal sensitivity.Qinling Mountains is the geographical dividing line of South and North China.It is located at the junction of warm temperate zone and subtropical zone.The climate throughout the year is characterized by distinct seasons and concentrated rainfall.Exploring the sensitivity of vegetation in the Qinling Mountains to dry and wet changes could reflect the response laws and mechanism characteristics of the main vegetation types in warm temperate and subtropical regions to dry and wet changes,which is of great significance for improving the prediction accuracy of terrestrial vegetation to climate change and deeply understanding the vegetation change laws in different climatic zones.This paper explored the spatiotemporal characteristics and spatial differences of the climate in the Qinling Mountains in the past 60 years using 32meteorological stations'monthly observed precipitation from 1959 to 2018.Combining the tree ring data of Larix chinensis and MODIS NDVI remote sensing data sets,the characteristics of spatiotemporal changes of NDVI and SPEI were studied,revealing the sensitivity and spatiotemporal differences of vegetation response to dry and wet changes in the Qinling Mountains.The following research results and progress have been achieved:?1?Spring showed a warming and drying trend,but changes in water and heat were not synchronized,and there were differences in spatial changes from 1959 to 2018 in the Qinling Mountains.This trend of warming and drying may continue in the future in spring.In the past 60 years,the spring temperature in the Qinling Mountains increased at a rate of0.33?·?10a?-1,the precipitation decreased at a rate of 4.90 mm·?10a?-1,and the SPEI value decreased at a rate of 0.14·?10a?-1.99.65%of the pixels showed a significant increase of temperature,64.46%of the pixels showed a significant decrease of precipitation,and75.28%of the pixels showed a significant decrease of SPEI value.In terms of spatial changes,there was a spatial difference in warming and drying in the Qinling region,showing a spatial pattern of"fast in the north and slow in the south".Sensitive areas that responded to spring climate change are located in Baoji,Zhouzhi,Huxian,Chang'an in the north of the Qinling Mountains,and Taibai,Zhashui,and Zhen'an in the south of the Qinling Mountains.The frequency and severity of droughts were higher from 1994 to 2008.The frequency and degree of droughts have been reduced after 2009.Morlet wavelet analysis and the Hurst index shown that the Qinling Mountains may continue this warming and drying trend in spring in the near future.?2?Based on the tree ring research,the radial growth of Larix chinensis in Taibai Mountain was more sensitive to the temperature from February to June,precipitation from March to May?spring?and SPEI from March to May?spring?,and its radial growth was mainly affected by climate fluctuations around spring.The radial growth of Larix chinensis in Taibai Mountain area was mainly restricted by the climate around spring,and had the highest correlation with SPEI value in spring,reaching-0.720?p?0.01?,and the variance interpretation of the reconstruction equation was 51.8%?51.0%after adjusting the degrees of freedom?.The reconstruction results showed that in the past 165 years,29 years were humid year and 23 years were dry year,accounting for17.58%and 13.94%,respectively.Extreme drought years were 1892,1929,1945 and 2006,extreme humid years were 1881,1921 and 1990,of which 1892?-1.73?and 1881?1.53?were the driest and most humid years.The reconstruction results of this paper have been verified by the reconstruction results of the dry and wet changes in the surrounding areas and the disaster records in the historical literatures;the dry and wet changes in the Taibai Mountain area could accurately characterize the dry and wet changes in large areas and there were periodic changes of 2.5a,3.1 a,3.8 a,and 8.4 a scales.The SPEI in the Taibai Mountain area was negatively correlated with the sea surface temperature in the eastern equatorial Pacific and positively correlated with the sea surface temperature in the western equatorial Pacific,and its dry and wet changes may be related to ENSO activity.?3?Based on NDVI remote sensing data research,the NDVI of the Qinling Mountains showed a significant upward trend from 2000 to 2018,and its changes were more susceptible to the first half of the year,especially dry and wet changes in spring.The vegetation on the northern slope of the Qinling Mountains was the most sensitive to the overall dry and wet changes from March to June.Vegetation on the southern slope was most sensitive to changes of dry and wet in spring?March to May?.The overall vegetation coverage of the Qinling Mountains improved significantly from2000 to 2018,while the NDVI rise rate and area ratio in the southern slope were higher than those in the northern slope,and the vegetation in the southern slope exhibited better improvement than that in the northern slope.The Qinling Mountains showed insignificant humidification trend.The humidification rate and humidification area of the northern slope were greater than those in the southern slope.Vegetation in the northern slope of the Qinling Mountains was more sensitive to hydrothermal dynamics than that in the southern slope.Vegetation in the northern slope was most sensitive to hydrothermal dynamics during March to June,while the southern slope during March to May?Spring?.The vegetation in the northern and southern slopes of the Qinling Mountains was mainly affected by hydrothermal dynamics on a scale of 3?7 months,and responds weakly to hydrothermal dynamics on a scale of 11?12 months.90.34%of NDVI and SPEI were positively correlated in the Qinling Mountains.Spring humidification in most areas could promote the growth of vegetation all year round.The sensitivity of vegetation response to hydrothermal dynamics with increasing altitude increased first and then decreased.The altitude of 800 to 1200 m was the most sensitive altitude for vegetation response to hydrothermal dynamics.The sensitivity of vegetation response in the elevation between1200 and 3000 m decreased with the increasing altitude.The grass was the most sensitive vegetation type to hydrothermal dynamics in the northern and southern slopes of the Qinling Mountains,but most of other vegetation types in the northern slope of the Qinling Mountains were more sensitive to hydrothermal dynamics than those in the southern slope.
Keywords/Search Tags:Vegetation in the Qinling Mountains, climate change in Spring, NDVI, sensitivity, spatial difference
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