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University of Electronic Science and Technology (2018)

Research on Drought Monitoring and Terrestrial Ecosystem Response Based on Multi-Source Remote Sensing Data

李星;

Titre : Research on Drought Monitoring and Terrestrial Ecosystem Response Based on Multi-Source Remote Sensing Data

Auteur : 李星;

Grade : Doctoral Dissertation 2018

Université : University of Electronic Science and Technology

Résumé
In the context of global warming,drought seems to be occurring more frequently,which has negative impacts on agriculture,water resources,natural ecosystems,and society activities.Drought is considered to be one of the most complex but least understood natural hazards,and it involves dynamics within the atmosphere-vegetation-soil continuum.In the past decades,scientists from different disciplines have proposed various drought indices to monitor the drought,aiming to explore the cause and duration of drought and also to understand how drought affects the terrestrial ecosystems.The traditional drought index based on site meteorological data can effectively monitor the drought conditions surrounding the meteorological stations,but can not be applied to characterize and monitor the detailed spatial pattern of drought conditions at regional scale.The emergence and development of remote sensing technology make it possible to monitor the drought in large-scale areas.The availability of spatio-temporal information for a variety of variables related to atmosphere,vegetation and soil conditions acquired based on different satellite sensors and remote sensing inversion methods benefits comprehensively monitor the drought conditions.This paper combines multi-source remote sensing data to monitor the drought conditions and explore the response of ecosystems to the drought in different areas.Multi-source remote sensing data used here include site meteorological data,gridded reanalysis meteorological data,eddy covariance(EC)flux data,and satellite remote sensing based vegetation indices and canopy variables.By analyzing the dynamic changes of different variables during the drought,we can comprehensively monitor the regional drought conditions and explore the mechanism of ecosystem response to climate change.This dissertation can shed light on the analysis of climate-vegetation interactions,ecosystem functions and the global carbon cycle.The main work are summarized as follows :(1)We firstly evaluated the performance of the standardized precipitation evapotranspiration index(SPEI)in monitoring the wet and dry conditions in southwestern China.The SPEI,an improved indicator of standardized precipitation index(SPI),incorporates temperature data for the calculation of potential evapotranspiration,and is more promising under the condition of global warming.In this study,monthly SPEI from1982 to 2012 was calculated using the precipitation and temperature data from 89meteorological stations in southwestern China,in order to provide a comprehensive analysis of the drought conditions.Based on the SPEI series for various time lags,the multi-scale patterns,the trend,and the spatio-temporal extent of drought were successively analyzed.In addition,two remote sensing based drought indices were used to explore whether the vegetation and soil moisture can respond to the SPEI.The results showed that SPEI can effectively monitor the drying trend of southwestern China and successfully captured the typical drought events occurring in recent years.The strong consistency between SPEI and two remote sensing based indices indicated that the SPEI can also characterize the drought conditions of vegetation and soil to a certain extent.(2)This paper also evaluated the feasibility of using the canopy water content(CWC)retrieved from the radiative transfer model to monitor the drought in a semi-arid grassland located in Qinghai Lake watershed.In our experiments,a widely used PROSAIL model combined with the Look-up Table(LUT)method were applied to retrieve the CWC.To improve the inversion efficiency,Sobol’sensitivity analysis method was used to decrease the dimensions of the“free”parameters in the PROSAIL model.We finally obtained multiple CWC maps in five selected years covering the different meteorological conditions for analyzing the response of CWC to drought.The results showed that the drought largely reduced the region-wide CWC values.It was explicit to distinguish the drought year from the wet and normal years in terms of the distributions of CWC values.Since the CWC relied on variations of both leaf area index(LAI)and equivalent water thickness(EWT)during the inversion process,it was considered to be more sensitive to the drought

Mots clés : Drought; ecosystem; remote sensing; vegetation indices; solar-induced chlorophyll fluorescence;

Présentation (CNKI)

Page publiée le 14 avril 2019