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Lanzhou University (2017)

Tree-ring-based Droughts Variability in Western Tianshan Mountains, Central Asia


Titre : Tree-ring-based Droughts Variability in Western Tianshan Mountains, Central Asia

Auteur : 张瑞波;

Grade : Doctoral Dissertation 2017

Université : Lanzhou University

Résumé partiel
Climate change is currently an issue of scientific challenge and political debate.Global warming has altered precipitation and the hydrologic cycle in various regions.Past global climate changes had strong regional expression.Especially the change of precipitation is strong locality,therefore,it is important to understand the regional droughts and pluvials change.Central Asia is a typical inland arid area,located on the upper reaches of westerly.There have fragile ecological environment,response sensitive to climate change.The Tianshan Mountains are known as the “water tower”,and are the largest and most important mountain system in the arid region of Central Asia,which has produced many civilizations of the central Asian.It is vital to understand the fact of past droughts variability.The length of instrumental meteorological observation data is limited,and thus,long-term climate change research has been restricted.Dendroclimatology is an important method for examining pre-instrumental climate change.The tree-ring of Schrenk spruce(Picea schrenkiana Mey)growing in arid and semi-arid mountainous environments is sensitive to climate and is very suitable for climate reconstruction.However,numerous climate reconstructions are concentrated in China.This dissertation is aimed at the weak areas and regions of the dendroclimatology in Tianshan Mountains.First of all,the intra-annual radial growth regularity of Schrenk spruce and its response to daily meteorological factors were revealed based on the dendrometer method.Then,many tree-ring samples were collected,and tree-ring width chronologies were established from western Tianshan Mountains,central Asian.The drought variability in Issyk Lake Basin of Kyrgyzstan,southern Kazakhstan and Dzungarian Alatau of the eastern Kazakhstan were reconstructed and analyzed,respectively.The regional differences and possible causes of the past drought variability in the western Tianshan Mountains were discussed.Finally,the main law of the past drought variability in the Tianshan Mountains is suggested.The main conclusions of this dissertation are summarized as follows : 1.The response of Schrenk spruce radial growth to climate1)Intra-annual radial growth response to daily meteorological factorsThe critical growing season of Schrenk spruce is from late May to late July and that the rapid growth stage is from mid-June to early July.Meanwhile,in the growing season,changes in the radial growth of Schrenk spruce were negatively correlated with daily temperature,evaporation,sunshine hours and vapor pressure deficit(VPD),and were positively correlated with precipitation and relative humidity(RH).The moisture plays a major role in the growth of Schrenk spruce.We suggest that precipitation between late May and late June is a limiting factor for radial growth of Schrenk spruce on the northern slopes of the Tianshan Mountains.2)Tree-ring width response to climateThe precipitation from previous July to current June has an important effect on the radial growth in Tianshan Mountains.The moisture before the growth season and the early growing season are the main limiting factor of the tree-ring width at the lower treeline in the Tianshan Mountains.3)Tree-ring width response to snow coverThere are significant positive correlation between radial tree growth and snow cover parameters(maximum snow depth,precipitation in winter,duration of snow cover ≥10 cm and duration of snow cover ≥1 cm).

Mots clés : Tianshan Mountains; Arid Central Asia; Tree-ring; Climate change; Droughts variability;

Présentation (CNKI)

Page publiée le 26 mai 2018