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Xi’an University of Technology (2021)

The Evolution of Dry-wet Compound and Their Effects on Vegetation in Typical Areas of the Yellow River Basin

史武智

Titre : The Evolution of Dry-wet Compound and Their Effects on Vegetation in Typical Areas of the Yellow River Basin

Auteur : 史武智

Grade : Master These 2021

Université : Xi’an University of Technology

Résumé partiel
Compared with a single drought or flood disaster,dry-wet compound events may have more adverse impact on crop production and food security.However,existing studies have paid seldom attention on the evolution characteristics of dry-wet compound events,and their driving factors and losses have not yet been revealed.To end this,firstly,the dry and wet events in adjacent seasons(spring-summer,summer-autumn,autumn-winter,winter-spring)in typical areas of the Yellow River Basin were evaluated based on the standardized precipitation index(SPI),and the joint return periods of various combinations of dry-wet,wet-dry,continuous dry,and continuous wet events under two scenarios(moderate and severe)were calculated using a copula function.The Mann-Kendall test was used to explore the joint return period dynamics with a 31-year sliding window.The Copula-based likelihood-ratio method and cross-wavelet transform were adopted to explore the driving forces of dry and wet combination dynamics.Secondly,taking the Wei River Basin(WRB),which is the largest tributary of the Yellow River Basin,as an example,the drought-flood abrupt transition index was defined to identify the drought-flood abrupt alternation(DFAA)events during the flood season of the WRB,and spatiotemporal evolution characteristics and future trend variability of DFAA events were explored.The driving factors of DFAA events were comprehensively evaluated using qualitative and quantitative combination framework.Finally,based on the annual scale and monthly scale,the vegetation cover dynamics in the WRB were analyzed using the GIMMS NDVI 3G dataset from 1982 to 2013.Pearson correlation coefficient method was used to determine the optimal response time of vegetation to spring-summer and summer-autumn DFAA events.A probabilistic different degrees under DFAA event stress.The main research results of this paper are as follows :(1)spring-summer and summer-autumn are prone to continuous dry(wet)events,while the probabilities of the combinations of dry and wet conditions occurring in autumn-winter and winter-spring are almost the same.Spatially,continuous wet events frequently occur above Longyang gorge and below Huayuankou,while the Inner flow area is prone to continuous dry events.(2)the risk of dry and wet combinations with high frequency decreases,whereas the risk of compound events with low frequency increases.The dependency structure dynamics of the SPI series between adjacent seasons show the strongest correlation with the El Nino-Southern Oscillation(ENSO),followed by the Arctic Oscillation and sunspot activities,implying that the ENSO has a dominant control on the dry and wet combination dynamics in the YRB.

Mots clés : Copula functions ; Joint return period ; Driving force ; Dynamics ; Drought-flood abrupt alternation ; Vegetation vulnerability ;

Présentation (CNKI)

Page publiée le 22 octobre 2021