Widespread droughts can have a significant impact on western United States streamflow, but the causes of these events are not fully understood. This dissertation examines streamflow from multiple western US basins and establishes the robust, leading modes of variability in interannual streamflow throughout the past century. I show that approximately 50% of this variability is associated with spatially widespread streamflow anomalies that are statistically independent from streamflow's response to the El Niño-Southern Oscillation (ENSO). The ENSO-teleconnection accounts for approximately 25% of the interannual variability in streamflow, across this network. These atmospheric circulation anomalies associated with the most spatially widespread variability are associated with the Aleutian low and the persistent coastal atmospheric ridge in the Pacific Northwest. I use a watershed segmentation algorithm to explicitly track the position and intensity of these features and compare their variability to the multi-basin streamflow variability. Results show that latitudinal shifts in the coastal atmospheric ridge are more strongly associated with streamflow's north-south dipole response to ENSO variability while more spatially widespread anomalies in streamflow most strongly relate to seasonal changes in the coastal ridge intensity. This likely reflects persistent coastal ridge blocking of cool-season precipitation into western US river basins. I utilize the 35 model runs of the Community Earth System Model Large Ensemble (CESMLE) to determine whether the model ensemble simulates the anomalously strong coastal ridges and extreme widespread wintertime precipitation anomalies found in the observation record. Though there is considerable bias in the CESMLE, the CESMLE runs simulate extremely widespread dry precipitation anomalies with a frequency of approximately one extreme event per century during the historical simulations (1920 - 2005). These extremely widespread dry events correspond significantly with anomalously intense coastal atmospheric ridges. The results from these three papers connect widespread interannual streamflow anomalies in the western US - and especially extremely widespread streamflow droughts - with semi-permanent atmospheric ridge anomalies near the coastal Pacific Northwest. This is important to western US water managers because these widespread events appear to have been a robust feature of the past century. The semi-permanent atmospheric features associated with these widespread dry streamflow anomalies are projected to change position significantly in the next century as a response to global climate change. This may change widespread streamflow anomaly characteristic in the western US, though my results do not show evidence of these changes within the instrument record of last century.

Identification of effects that climate teleconnections, such as El Nino-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and North Atlantic Oscillation (NAO), have on wildfires is difficult because of short and incomplete records in many areas of the world. We developed the first multicentury wildfire chronologies for northeast China from fire-scarred trees. Regional wildfires occurred every 7years from the 1700s to 1947, after which fire suppression policies were implemented. Regional wildfires occurred predominately during drought years and were associated with positive phases of ENSO and PDO and negative NAO. Twentieth century meteorological records show that this contingent combination of +ENSO/+PDO/-NAO is linked to low humidity, low precipitation, and high temperature during or before late spring fire seasons. Climate and wildfires in northeast China may be predictable based on teleconnection phases, although future wildfires may be more severe due to effects of climate change and the legacy of fire suppression.

Dans un contexte où l'irrigation est une pratique devenue essentielle aux équilibres alimentaires sur la planète, plus particulièrement dans le cadre d'une augmentation des aléas climatiques, les systèmes de tarification non linéaire peuvent jouer un rôle déterminant pour la répartition de la ressource en eau, tout en respectant différentes contraintes de gestion telles que la couverture des coûts. Récemment, en France, certaines compagnies de gestion de l'eau d'irrigation ont mis en place de tels systèmes originaux de tarification fondés sur une différenciation entre des volumes d'eau réservés et des volumes réellement consommés. Ce travail a un double objectif : il vise, d'une part, à évaluer, sur différents plans, ces nouveaux systèmes de tarification mis en place et d'autre part, à concevoir des méthodes de tarification non linéaires capables d'intégrer les risques liés à la variabilité de la disponibilité de l'eau. La thèse est organisée en deux parties. La première partie est composée de 2 chapitres qui fournissent des éléments de cadrage sur la gestion de l'eau d'irrigation et expliquent la problématique de la recherche. La deuxième partie est composée de 4 chapitres constituant chacun un article. Dans le chapitre 3, nous évaluons l'efficacité de systèmes de tarification non linéaire de l'eau d'irrigation mis en place par des compagnies d'eau en France en prenant en compte les aléas pluviométriques et nous proposons des pistes d'amélioration de ces systèmes. Le chapitre 4 se situe dans la continuité du précédent dans la mesure où une méthodologie similaire est utilisée. Il compare ces nouveaux systèmes de tarification à une tarification uniforme dans un contexte de rareté de l'eau d'irrigation et d'aléas climatiques. Les résultats montrent que ces systèmes sont d'autant plus efficaces que la tarification uniforme que la ressource est rare. Le chapitre 5 modélise une situation où les agriculteurs ont la possibilité de réserver de l'eau dans des stocks de niveaux de sécurité différents. Nous déterminons la tarification optimale sous trois hypothèses d'objectif de gestion : i) Le gestionnaire cherche à maximiser le bien-être social ; ii) Le gestionnaire cherche à maximiser le bien-être social mais en assurant l'équilibre budgétaire ; iii) Le gestionnaire cherche à maximiser son profit. Le chapitre 6 étudie la situation d'un gestionnaire qui a besoin d'informations sur la demande d'eau d'irrigation avant de transférer la ressource vers les périmètres irrigués. C'est le cas du système Neste où les réserves d'eau sont souvent très éloignées des périmètres agricoles. En plus, les agriculteurs sont confrontés à des aléas sur la pluviométrie qui peuvent altérer la précision de leur connaissance de leur demande d'eau future. Dans un tel contexte, nous développons un système de tarification avec des possibilités de réservations sur plusieurs périodes et nous déterminons la tarification optimale que doit appliquer le gestionnaire. La discussion des résultats de ces chapitres permet de proposer des recommandations par rapport à la conception de systèmes de tarification adaptés à la gestion d'une ressource et d'une demande en eau incertaines. / In a world where irrigation has become essential to balance global food production, especially in the context of increasingly variable climate conditions, nonlinear pricing systems can play a crucial role in the allocation of water resources, while respecting various management constraints such as cost recovery. Recently in France, some irrigation water management companies have implemented such innovative systems based on price differentiation between volumes of water reserved and volumes actually consumed. This work has two objectives: firstly it aims to assess, at different levels, the new pricing systems in place; secondly it seeks to devise methods of nonlinear pricing that can integrate the risks related to the variability of the availability of water. The thesis is organized into two parts. The first part (chapters 1 and 2) provides background information on irrigation water management and explains the research problem. In the second part (chapter 3 to 6) each chapter is an article. In chapter 3, we assess the effectiveness of nonlinear pricing systems implemented by water companies in France, taking into account the variability of rainfall. We analyze the advantages of these new pricing systems for managing climate variability. We suggest ways of improving these systems. Chapter 4 is in line with the previous chapter in that a similar methodology is used. It compares the new pricing systems to uniform pricing in a context of scarce irrigation water and variable climate conditions. The results show that nonlinear systems are even more efficient than uniform pricing when water scarcity is severe. Chapter 5 models a situation where farmers are offered the possibility of reserving water in stocks with different security levels. We determine optimal pricing for three management assumptions: i) The manager seeks to maximize social welfare, ii) The manager seeks to maximize social welfare while ensuring a balanced budget; iii) The manager seeks to maximize his/her profit. Chapter 6 addresses the situation of a manager who needs information on water demand before moving the resource to areas requiring irrigation. This is the case of the Neste system where water supplies are often far away from agricultural areas. In addition, farmers face uncertainty of rainfall that can alter the accuracy of their knowledge of their future water demand. In this context, we develop a pricing system with the possibility of reservations over several periods and determine the optimal pricing to be implemented. Our results provide guidelines for designing pricing schemes adapted to the management of an uncertain water resource and an uncertain demand.

Nous avons étudié les réponses à la contrainte hydrique du système biologique formé par l'association plante hôte – communautés de champignons ectomycorhiziens (ECM) en prenant comme espèces modèles deux chênes méditerranéens correspondant à des types biologiques contrastées décidu (Quercus pubescens) et sempervirent (Q. ilex). Nous avonstesté l'hypothèse selon laquelle les interactions fonctionnelles entre plantes hôtes et communautés associées pourraient être régulées par le niveau de ressource hydrique. A l'aide d'une expérimentation réalisée en conditions contrôlées, nos résultats ont montré que Q. pubescens réduisait davantage sa production que Q. ilex en réponse au déficit hydrique. La colonisation racinaire par les champignons ECM a varié selon les deux chênes et la disponibilité de l'eau. La longueur des racines colonisées était positivement corrélée à la croissance des plantes et à l'immobilisation des nutriments chez l'espèce décidue Q.pubescens mais pas chez Q. ilex. In natura, nous avons testé les traits de communautés ectomycorhiziennes dans un gradient environnemental de trois forêts de Q. ilex. Sur chaque site, le taux de colonisation racinaire et la richesse des espèces ECM ont diminué avec l'horizon échantillonné alors que parallèlement les ECM de la famille dominante Russulaceae augmentaient. Sur tous les sites, le type d'exploration dit «contact» était dominant, particulièrement dans le site sec. La composition des espèces a varié considérablement d'un site à l'autre avec un nombre élevé d'espèces rares, à l'échelle locale et à l'échelle régionale. Dans les trois sites, l'application d'une perturbation de sol de faible dimension a induit uneréponse forte de la communauté ECM. La diversité spécifique et la richesse ont diminué après la perturbation avec la disparition de la plupart des espèces de Russulaceae, de Cantharellaceae et de Clavulinaceae. Les types d'exploration contact ont fortement diminué alors que les types courte distance ont répondu positivement à la perturbation. Une mosaïque d'espèces stress-tolérantes comprenant plusieurs espèces des genres Sebacina sp et Helvellasp, ont dominé les communautés après la perturbation. Ces travaux apportent des éléments de compréhension du fonctionnement et de la réponse du système chênes méditerranéens - communautés ECM face à la contrainte climatique, les expérimentations in natura permettant d'affiner notre connaissance des stratégies écologiques de recolonisation ectomycorhizienneaprès perturbation. / The effect of drought had been investigated on the biological system -host plantectomycorrhizal community ECM- using different approaches. In a first part, we evaluated the drought-resistance of Quercus species and their associated ECM fungi, comparing the responses of two oak species differing in their leaf habitat, Q. pubescens vs Q. ilex (deciduous vs evergreen) in a controlled experiment. Our results showed that Q. pubescens reduced more its production than Q. ilex according to drought treatments. The total length of colonized fine roots was positively correlated with plant growth and nutrient immobilization in Q. pubescens but not in Q. ilex. In a second part, we investigated ECM community traits in three Q. ilex forests across an environmental gradient. At each site, both ectomycorrhizal colonization rate and species richness decreased with increasing soil depth, while the dominant family Russulaceae increased in abundance with increasing soil depth. At all sites, contact exploration type strongly dominated, with the highest abundance in the driest site. Species composition varied significantly across sites with high number of rare species at local and regional scales. At all sites, the application of an experimental soil disturbance provoked strong responses of the ECM community. Species richness and diversity decreased after disturbance with disappearance of numerous species of Russulaceae, Cantharellaceae and Clavulinaceae. The relative abundance of contact exploration types decreased after the disturbance whereas the opposite pattern was observed for short distance exploration type. A mosaic of stress-tolerance species of Sebacina sp and Helvella sp, dominated after disturbance. These studies provide an understanding of the functioning and the responses of the system Mediterranean oaks – ECM communities facing climatic constraints. In natura experiments provide us insights on our understanding of ecological strategies of ectomycorrhizal fungi after disturbance.

The interactions between vegetation and climate are complex and critical to our ability to predict and mitigate climate change. Savanna ecosystems, unique in their structure and composition, are particularly dynamic and their carbon cycling has been identified as highly significant to the global carbon budget. Understanding the responses of these dynamic ecosystems to environmental conditions is therefore central to both ecosystem management and scientific knowledge. Longleaf pine ecosystems are highly biodiverse and unique savanna ecosystems located in the south-eastern USA – an important current carbon sink and key area identified for future carbon sequestration. These ecosystems depend on fire to maintain their structure and function, and the longleaf pine tree itself (Pinus palustris Mill.) has been noted for its resilience to drought, fire, pests and storms and is thus becoming increasingly attractive as both a commercial forestry species and a provider of other ecosystem services. Previous process-based models tested in the south-eastern USA have been shown to fail in conditions of drought or rapid disturbance. Consequently, in order to inform management and understand better the physiology of these ecosystems, there is a need for a process-based model capable of upscaling leaf-level processes to the stand scale to predict GPP of longleaf pine savannas. P.palustris exists across a wide range of soil moisture conditions, from dry sandy well-drained soils (xeric) to claypan areas with higher moisture content (mesic). Previous work has demonstrated that this species adjusts many aspects of its physiology in response to these differing soil conditions, even under identical climate. The research in this thesis supports these previous findings, but additionally explores, with the assistance of the Soil Plant Atmosphere model (SPA), the productivity response of P. palustris across the soil moisture gradient. Contrary to expectations, measurements, field observations and modelling suggest that P. palustris trees growing in already water-limited conditions cope better with exceptional drought than their mesic counterparts. At the leaf-level, xeric P. palustris trees were found to have higher measured net photosynthesis, but the lower stand density and leaf area at this site meant that in non-drought conditions mesic P. palustris annual gross primary productivity (GPP) was 23% greater than xeric annual GPP. Initial upscaling of leaf-level processes to the canopy scale using the SPA model found that, during the growing season when other components of longleaf pine ecosystems are active, the longleaf pine may only be responsible for around 65% of the total productivity. Other important components of longleaf pine savannas are oaks and grasses which, with pine, constitute 95% of longleaf pine ecosystem biomass. Each of these groups, however, responds differently to fire and water availability. Despite this, the other components of longleaf pine savannas have received limited research attention and have never been modelled using a process-based model such as SPA. As integral components of longleaf pine carbon budgets, it is essential that the physiology and productivity of oaks and grasses in this system are better understood. The research in this thesis studied the productivity response of these groups during drought across a soil moisture gradient, and found that oak and pines at each site appear to fill separate ecohydrological niches depending on whether or not they are growing in a xeric or mesic habitat. As expected, the highest drought tolerance was found in the C4 grass, wiregrass (Aristida stricta), at both xeric and mesic sites. In order to further explore the contributions of the different functional groups in longleaf pine savannas, the SPA model was adapted to run with concurrent functional groups and to represent the different photosynthetic pathways of the understorey grasses (C4) and the canopy trees (C3). The aim of this part of the thesis was to represent better a savanna ecosystem in a process-based model and explore and quantify the contributions of each functional group diurnally, seasonally, annually and interannually. Modelling results suggest that accurately representing the phenology not only of trees but of grasses, is critical to capturing ecosystem GPP and its variability. This phenology may not only be seasonally controlled, but also dictated by fire. Overall, this research highlights the importance of continued research into savanna and savanna-like ecosystems. Additionally, it provides an insight into the responses of multiple ecosystem components to an extreme drought, and how these responses differ at leaf, stand and landscape scales. The thesis also employs a little-used method of combining eddy-covariance data with a process-based model to separate out different ecosystem components, a method becoming more common but not yet widely tested.

Doctor of Philosophy / Department of Agronomy / Jianming Yu / Knowledge of the genetic bases of grain quality traits will complement plant breeding efforts to improve the end use value of sorghum (Sorghum bicolor (L.) Moench). The objective of the first experiment was to assess marker-trait associations for 10 grain quality traits through candidate gene association mapping on a diverse panel of 300 sorghum accessions. The 10 grain quality traits were measured using the single kernel characterization system (SKCS) and near-infrared reflectance spectroscopy (NIRS). The analysis of the accessions through 1,290 genome-wide single nucleotide polymorphisms (SNPs) separated the panel into five subpopulations that corresponded to three major sorghum races (durra, kafir, and caudatum), one intermediate race (guinea-caudatum), and one working group (zerazera/caudatum). Association analysis between 333 SNPs in candidate genes/loci and grain quality traits resulted in eight significant marker-trait associations. A SNP in starch synthase IIa (SSIIa) gene was associated with kernel hardness (KH) with a likelihood ratio–based R[superscript]2 (R[subscript]L[subscript]R[superscript]2) value of 0.08. SNPs in starch synthase (SSIIb) gene (R[subscript]L[subscript]R[superscript]2 = 0.10) and loci pSB1120 (R[subscript]L[subscript]R[superscript]2 = 0.09) was associated with starch content. Sorghum is a crop well adapted to the semi arid regions of the world and my harbor genes for drought tolerance. The objective of second experiment was to identify quantitative trait loci (QTLs) for yield potential and drought tolerance. From a cross between Tx436 (food grain type) and 00MN7645 (drought tolerant) 248 recombinant inbred lines (RILs) was developed. Multi-location trials were conducted in 8 environments to evaluate agronomic performance of the RILs under favorable and drought stress conditions. The 248 RILs and their parents were genotyped by genotyping-by-sequencing (GBS). A subset of 800 SNPs was used for linkage map construction and QTL detection. Composite interval mapping identified a major QTLs for grain yield in chromosome 8 and QTL for flowering time in chromosome 9 under favorable conditions. Three major QTLs were detected for grain yield in chromosomes 1, 6, and 8 and two flowering time QTLs on chromosome 1 under drought conditions. Six QTLs were identified for stay green: two on chromosome 4; one each on chromosome 5, 6, 7, and 10 under drought conditions.

Doctor of Philosophy / Department of Agronomy / Allan K. Fritz / Heat and drought stress are two of the most significant abiotic stresses limiting wheat production in the Great Plains and worldwide. Introgression of novel tolerance genes from wild relatives is a strategy which presents promise. This study examined both heat and drought tolerance from the tetraploid species Aegilops geniculata (U[superscript g]U[superscript g]M[superscript g]M[superscript g]). Additional screening for heat tolerance was conducted with the US genome species Aegilops peregrina (Hack) and Aegilops kotschyi (Boiss). A comprehensive screening system for drought tolerance was also constructed to evaluate wheat and its wild relatives. Previous reports suggested that Ae. geniculata accession TA2899 was moderately tolerant to heat stress. It had also previously been used to develop a full set of wheat-Ae. geniculata chromosome addition lines in a Chinese Spring background. To identify the chromosome(s) carrying the heat tolerance, all addition lines, as well as wheat check genotypes, were screened for post-anthesis heat tolerance in two growth chamber experiments. No chromosome addition lines were significantly different (p<0.05) from Chinese Spring, and none were found to have superior performance to the positive check cultivars. Forty-five accessions of Ae. peregrina and its close relative, Ae. kotschyi were screened in a post-anthesis heat experiment. A follow-up experiment compared the genotypes in a split-plot temperature treatment with heat and optimal growth chambers. Many accessions were similar to the control genotypes for grain fill duration, and some exceeded the wheat controls for relative chlorophyll index values on Day 12 and Day 16. TA1889 and TA1904, both Ae. peregrina accessions originating from Israel, had a higher grain fill duration across experiments than the best wheat control, and warrant further investigation. Previous reports suggested drought tolerance in Ae. geniculata. After preliminary screenings, six genotypes were selected for advanced screening and compared with three wheat cultivars. The advanced greenhouse screening system was conducted in 152cm tall PVC growth tubes. The experiment measured multiple plant responses, and had a datalogging system automatically collecting water content and matric potential of the growth media. Multiple accessions warranted further investigation, and showed potentially different modes of drought tolerance, with varying levels of stomatal resistance, biomass, and osmotic adjustment.

La gestion d'une ressource en eau souterraine utilisée pour l'irrigation est un phénomène dépendant de plusieurs facteurs et concernant différents acteurs (utilisateurs et gestionnaire). En cas d'aléa climatique comme la sécheresse, gérer une ressource devient un problème plus complexe. Il est justement important de mieux comprendre et d'anticiper les sécheresses car ils peuvent avoir des impacts significatifs sur l'activité économique agricole et sur les niveaux de la ressource. Pour cela, le type d'information dont disposent les utilisateurs et/ou les gestionnaire est essentiel. Dans les chapitres 2 et 3, nous analysons l'impact d'une sécheresse "hydrologique" sur la gestion optimale de la ressource, avant et après son arrivée. Dans le chapitre 2, nous montrons comment le gestionnaire de la ressource peut s'adapter le mieux possible à cette sécheresse selon l'information dont il dispose. Dans le chapitre 3, nous montrons que la prise en compte des interactions stratégiques et dynamiques entre les utilisateurs de la ressource entraîne une exploitation moins efficace de la ressource. Nous appliquons les modèles des chapitres 2 et 3 à l'aquifère La Mancha Occidentale au Sud de l'Espagne. Dans le chapitre 4, nous analysons l'impact d'une sécheresse "agronomique" sur la gestion optimale d'une exploitation agricole située dans la zone de la Beauce centrale, en France. Nous prenons en compte des informations de caractère hydrologique, agronomique et économique. En particulier, nous étudions l'impact d'une année sèche sur la valeur ajoutée de l'exploitation et sur la ressource en eau utilisée. De plus, nous nous intéressons au comportement stratégique que les agriculteurs peuvent avoir en année sèche, que ce soit sans ou avec restrictions des usages de l'eau. Nous montrons qu'une politique de régulation est nécessaire pour éviter la surexploitation de la nappe en année sèche. / The management of a groundwater resource used for irrigation is a phenomenon that depends on several factors and concerning various actors (users and manager). Moreover, the resource can be subject to droughts. In this case, the management of the resource becomes a more complex problem. Adaptation to droughts is important because they can have significant impacts on agriculturalactivity and on the water table of the resource. This adaptation hinges crucially on the information available to the manager and the resource users. In chapters 2 and 3, we analyze the impact of an hydrological drought on the optimal management of the resource, before and after its arrival. In particular, in chapter 2, we show how the manager can adapt as good as possible to this drought according to the nature of information he has. In chapter 3, we are show that taking into account strategic and dynamic interactions between the users of the ressource leads to less efficient resource use. We apply models of chapters 2 and 3 to the aquifer Western La Mancha, in Spain. In chapter 4, we study the impact of an agronomic drought on the optimal management of a farm in the area of Central Beauce, in France. We take into account hydrological, agronomic and economic informations. In particular, we analyze the impact of a dry period on the annual benefits of the farm and on the groundwater resource level. Furthermore, we study optimal strategic behavior of farmers in a dry year, whether they are subject to water restrictions or not. We show that a regulation policy is necessary to avoid the overexploitation of the ressource in a dry year.

>Magister Scientiae - MSc / Maize is one of the most abundantly produced cereals and contributes to about 40% of the global cereal production. This figure will have to increase in order to feed the ever-growing human population. One of the major environmental constraints that impact maize production is drought. Plants use antioxidant defences to cope with drought stress. Understanding and improving these defence mechanisms will be important to improve overall drought tolerance. A previous study done by Gokul and authors in 2016 showed that 3,3’-diindolylmethane (DIM) improves both seed germination and seedling shoot growth in Brassica napus. Plants belonging to the Brassicaceae family have the metabolic machinery to synthesize glucosinolates such as DIM, which play vital roles in physiological and stress responses. These responses have not been investigated in plants such as maize, which lack the machinery to produce DIM. Therefore, this study investigated the effects of exogenously applied DIM on the physiological and biochemical responses of maize under drought stress. Physiological parameters such as relative water content, chlorophyll content and lipid peroxidation, were determined in order to understand how drought and DIM , as separate or combined treatments, affected the plants. Additionally, proline accumulation was also assessed because free proline plays a role as an osmoprotectant during stress. The accumulation of ROS, namely hydrogen peroxide, was measured using spectrophotometric assays to determine how the above treatments affect ROS accumulation in maize. As a result of changes in the ROS content in due to the treatments, it would only be natural to investigate the changes in antioxidants as well. Given that hydrogen peroxide was the ROS to be measured, we therefore investigated the antioxidant enzymatic activities responsible for hydrogen peroxide scavenging. Therefore, changes in Ascorbate peroxidase (APX) and catalase (CAT) were assessed. An improved drought response was observed in maize plants treated with DIM as these plants had better ability to maintain their water status than when no DIM was applied. This is indicated by water-deprived plants treated with DIM having a higher RWC than water-deprived plant without DIM.

干旱是全球范围内的灾害。协同利用遥感数据和气象数据来研究植被对干旱的响应并进行干旱评估和监测，对于减少干旱损失，制定决策和农业管理都有重大的现实意义。 / 本研究提出了两种新的处理多时相遥感数据的方法：一种是基于无云影像频域分析的植被时间序列获取；另一种是基于时间序列主成份分析的MODIS混合象元信息提取。这两种方法可以分别用于时间序列数据的预处理和估算生态干扰发生时陆地植被覆盖的变化。 / 本研究开展了地面试验，用ASD地面高光谱仪和SPAD502叶绿素仪测定了在控制梯度干旱下的玉米叶片光谱和叶绿素含量的动态变化。研究表明：随着干旱的加剧, 叶片光谱反射率也会相应增加。统计分析表明叶片510 nm和690 nm处的反射率可以用于玉米干旱的预警。本研究基于不同干旱程度和玉米不同发育时期的光谱数据，全面探讨了光谱变量和光谱指数对干旱胁迫下叶绿素变化的敏感性。 / 本研究探讨了中国的作物长势与气象因子的关系，首先基于温度，降水，光照和NDVI数据将中国分为7个研究区，然后基于多元线性回归提取了每个研究区在19822006年间限制作物生长的关键气候因子。研究表明在春季和夏季，温度，降水, 光照对作物NDVI的影响（R²>=0.35）要大于秋季和冬季 (R²<=0.14). 在分区1-3（华北，东北）中，全年作物NDVI呈现显著增加的趋势(p<0.1)，而在华南地区则没有明显的趋势。 / 在西南干旱中，两类遥感干旱指数（基于空间特征的TVDI和基于时间序列的VHI）与气象干旱指数SPI进行了比较。本研究进行了气象干旱指数和遥感干旱指数的时空一致性分析。TVDI受制于特定研究区提取的‘干边’和‘湿边’，而VHI则受时间序列数据噪声的影响。SPI36和遥感干旱指数存在相对稳定的关系，这与研究区的主要的植被类型是森林有关。 / 本研究用模型碳参数结合遥感数据估算了干旱引起的森林生态系统碳存储的变化。估算的结果与遥感获取的植被净光合速率的变化进行了比较，两者的一致性较高（r=0.32 p<0.001）。研究表明卫星遥感数据结合生态模型可以有效反演在全球变化背景下植被参数的变化。 / Studies on monitoring vegetative responses to drought by integrating remote sensing and meteorological data sets are of great practical meaning in mitigating losses, making decisions and managing agriculture. / A field experiment was conducted to test the hyperspectral sensitivity of corn responses to drought in controlled gradients. Statistical analysis shows that leaf reflectance at 510 nm and 690 nm under artificial illumination mode can indicate early drought significantly. The sensitivity of different hyperspectral indices and position-based variables on vegetative chlorophyll change under drought was also comprehensively compared. / China was divided into 7 regions based on the monthly anomaly of NDVI, precipitation, temperature and sunshine duration from 1982 to 2006 with hierarchical clustering. The impact of precipitation, temperature and sunshine duration on crop NDVI in spring and summer (average R² >=0.35) is higher than that in autumn and winter (average R² < =0.14). The full-year crop NDVI trend for region 1-3 increases (p<0.1), which is related with temperature increase as temperature is the limiting climatic factor for crop growth in these regions. / Time-frequency domain analysis was conducted to denoise multi-temporal remotely sensed data. These methods can be used for retrieving cloud-free phenological curves from multi-temporal satellite data. The two drought indices TVDI and VHI were spatio-temporally compared with the meteorological drought index, SPI. TVDI was subjected to extracted ‘wet edge’ and ‘dry edge’ in the study area while VHI was subjected to noises on NDVI and LST time series. SPI36 and remotely sensed drought indices can reach relative stable relationship, which may be due to the fact that most areas in the present study were covered by forest. / Carbon dynamics for forest ecosystem in drought can be quantified with carbon parameters from models and multi-temporal MODIS NDVI data sets. Sub-pixel percent forest cover was extracted based on principle component analysis (PCA) to multi-temporal MODIS NDVI. The estimated carbon change is highly correlated with the remotely sensed PsnNet change (r=0.32 p<0.001). Satellite remote sensing in conjunction with ecological models can retrieve many important variables caused by global change. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wang, Hongshuo. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 102-120). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Abstract --- p.I / Table of contents --- p.IV / List of figures and tables --- p.VII / Acknowledgement --- p.XI / Chapter CHAPTER 1 --- Introduction --- p.1 / Chapter 1.1 --- Significance of the research --- p.1 / Chapter 1.2 --- Objectives of the study --- p.4 / Chapter 1.3 --- Dissertation structure --- p.4 / Chapter CHPATER 2 --- Literature Review --- p.6 / Chapter 2.1 --- Review on denoising multi-temporal data with time-frequency domain analysis --- p.6 / Chapter 2.2 --- Review on sub-pixel information extraction with multi-temporal NDVI --- p.9 / Chapter 2.3 --- Review on sensitivity of hyperspectral data in drought monitoring --- p.11 / Chapter 2.4 --- Review on spatio-temporal crop responses to climate change in China --- p.15 / Chapter 2.5 --- Review on spatio-temporal assessment of remotely- sensed drought indices --- p.18 / Chapter 2.5.1 --- Meteorological drought monitoring --- p.18 / Chapter 2.5.2 --- LST/NDVI space and its significance in drought monitoring --- p.20 / Chapter 2.6 --- Review on retrieving terrestrial carbon flux in drought --- p.23 / Chapter CHAPTER 3 --- Sensitivity of Hyperspectral Data in Monitoring Corn Responses to Drought --- p.25 / Chapter 3.1 --- Experiment --- p.25 / Chapter 3.2 --- Data analysis --- p.28 / Chapter 3.2.1 --- Sensitivity of hyerpspectral data to drought severity --- p.28 / Chapter 3.2.2 --- Comparison of different vegetation indices under drought --- p.30 / Chapter 3.3 --- Chlorophyll gradient under the threat of drought --- p.35 / Chapter 3.4 --- Discussion and conclusion --- p.36 / Chapter CHAPTER 4 --- Spatio-temporal Crop Responses to Climate Change in China --- p.39 / Chapter 4.1 --- Data description and preprocessing --- p.39 / Chapter 4.1.1 --- Data sets --- p.39 / Chapter 4.1.2 --- Data preprocessing --- p.40 / Chapter 4.1.3 --- Data standardization --- p.41 / Chapter 4.2 --- Conducting clustering analysis --- p.41 / Chapter 4.3 --- Regionalization result --- p.44 / Chapter 4.4 --- Crop responses to climate change --- p.44 / Chapter 4.4.1 --- Full-year crop responses to climate change --- p.48 / Chapter 4.4.2 --- Seasonal crop responses to climate change --- p.48 / Chapter 4.5 --- Drought trend of different scales and its potential influences on crop production --- p.54 / Chapter 4.6 --- Conclusion --- p.55 / Chapter CHAPTER 5 --- Spatio-temporal Assessment of Remotely-sensed Drought Indices a Case Study in Drought of Southwest China --- p.57 / Chapter 5.1 --- Denoising Multi-temporal data with frequency-time domain analysis --- p.57 / Chapter 5.1.1 --- Data Description --- p.57 / Chapter 5.1.2 --- Methods --- p.59 / Chapter 5.1.3. --- Comparison among Different Methods --- p.64 / Chapter 5.2. --- Drought indices --- p.65 / Chapter 5.2.1 --- data preprocessing --- p.67 / Chapter 5.2.2 --- VHI --- p.68 / Chapter 5.2.3 --- TVDI --- p.68 / Chapter 5.2.4 --- Spatial consistency between TVDI and VHI --- p.75 / Chapter 5.3 --- Conclusion and Discussion --- p.76 / Chapter CHAPTER 6 --- Monitoring Carbon Dynamic during Drought in Southwest China with MODIS --- p.78 / Chapter 6.1 --- Sub-pixel information retrieval based on multi-temporal MODIS NDVI --- p.78 / Chapter 6.1.1 --- Data collection and processing --- p.78 / Chapter 6.1.2 --- Methods --- p.82 / Chapter 6.1.3 --- Results and analysis --- p.86 / Chapter 6.2 --- Determining drought period --- p.89 / Chapter 6.3 --- Quantifying vegetative responses to drought with vegetation indices --- p.91 / Chapter 6.4 --- Quantifying carbon change of forest ecosystem during drought --- p.92 / Chapter 6.5 --- Conclusions and Discussions --- p.95 / Chapter CHAPTER 7 --- Innovations and Future Works --- p.98 / Chapter 7.1 --- Summary --- p.98 / Chapter 7.2 --- Innovations --- p.99 / Chapter 7.3 --- Future work --- p.101 / Reference --- p.102