Drought is a well-known and costly climate-related natural hazard. Unlike other climate-related natural hazards, droughts are usually long in duration and may cover a large region, the physical boundaries of areas affected by drought are sometimes arbitrary, and the impacts are sometimes difficult to identify. Climate records since 1895 show that drought has occurred periodically in Kentucky. The drought of 2007 was the most recent drought to affect Kentucky and is the primary focus of this research. The purpose of this research is to identify impacts of drought and potential vulnerabilities to various drought impact sectors in Kentucky so that policymakers can develop a drought plan that addresses these vulnerabilities and emphasizes mitigation efforts. An historical analysis of drought was provided for the following droughts that occurred in Kentucky: 1930-31, 1940-42, 1952-55, 1987-88, and 1999-2001. A more indepth analysis of the development and impacts of the drought of 2007 was conducted. Weekly drought reports from the drought of 2007 that were published by the Kentucky Division of Water were used for analysis.The reports discussed streamflows, PDSI values, precipitation deficits, lake levels reports from the U.S. Army Corps of Engineers, and other information that documented the progress of the drought. Impacts caused by the drought of 2007 were identified mostly through news reports. Agriculture and water supplies were determined to be most impacted by drought; therefore, two separate surveys (one regarding drought impacts on agriculture in 2007, the other regarding drought impacts on water supplies in 2007) were created to increase the understanding of how the drought of 2007 affected agriculture and water supplies in Kentucky. Other impacts from the drought of 2007 that were studied include impacts on recreation and tourism, the number of fires and wildland fires, plant and animal species, and small businesses. It was found that droughts that have affected Kentucky have originated in all directions and have spread northward, southward, eastward, and westward into Kentucky. The temporal scale of these droughts has also varied. Impacts caused by the drought of 2007 in Kentucky were very similar to impacts caused by historical droughts. However, the documentation of drought impacts that occur in Kentucky needs improvement. Agricultural impacts are documented better than any other impact, while impacts on water supplies, recreation and tourism, the occurrence of wildland fires, plant and animal species, and small businesses are not as well documented. It is recommended that conducting an extensive analysis of how various sectors are vulnerable to drought in Kentucky and educating the public on the importance of drought awareness should be addressed by policymakers involved in the development of Kentucky’s state drought plan.

The interaction of tick species and the microclimate that they inhabit is a subject that is frequently studied. The known biology of the Gulf Coast tick, Amblyomma maculatum Koch (Acari: Ixodidae), was used to conduct analyses to determine which meteorological factors regulate Gulf Coast tick survivorship in an area of Texas that is known for reduced occurrence of this tick species. Gulf Coast tick collection records, that indicated the collection of a single tick or multiple ticks from one animal or multiple animals at livestock markets, were obtained from the Texas Animal Health Commission. These records were used as an indicator of adult Gulf Coast tick abundance during each year in the 90 county study area and were used as the dependent variable in linear, quadratic, and cubic regression analyses. Independent variables used in these analyses were precipitation and differing drought thresholds during the peak activity time of the four life stages of the Gulf Coast tick and during combined life stage peak activity times. Linear, quadratic, and cubic regression analyses to measure the effect of precipitation during differing peak activity times of the Gulf Coast tick on adult Gulf Coast tick collection records were not statistically significant. These three regression analyses were also used to measure the effect of increasing drought thresholds, measured using a Keetch-Byram Drought Index, on adult Gulf Coast tick collection records. A determination was made that increasing drought thresholds during the peak activity time of differing Gulf Coast tick life stages reduce the number of Gulf Coast tick collection records the following year.

Population based association studies in crops that were established by domestication and early breeding can be a valuable basis for the identification of QTLs. A case control design in a population is an ideal way to identify maximum candidate sites contributing to a complex polygenic trait such as drought. In the current study, marker loci associated with drought related QTLs were identified in sugarcane (Saccharum spp), one of the most complex crop genomes, with its polyploid nature (>8), chromosome number (>100) and interspecific origin. The objectives of this investigation were: 1) development of genic markers, which can be used for marker-assisted selection of drought tolerant genotypes of sugarcane. 2) genotypic characterization of sugarcane population at drought related loci using EST-SSR markers. Using 55 microsatellite markers, 56 polymorphisms were scored among 80 modern sugarcane genotypes. Homogeneity of the population was confirmed by determining the distribution of allele frequencies obtained by random genomic microsatellite markers. This analysis was conducted in the STRUCTURE program and the population was divided in 3 subgroups based on the allelic distribution. Phenotypic data to evaluate drought tolerance among the genotypes was collected by measuring chlorophyll content, chlorophyll fluorescence, leaf temperature and leaf relative water content. A generalized linear model in SPSS was used to find association between marker loci and phenotypic data. Markers with significant association (P 0.001 level) with the trait were subjected to linear regression to screen the spurious associations. Based on the results, 21 EST-SSR markers and 11 TRAP markers related to drought-defining physiological parameters were considered as genuine associations in this study. Fifty-six polymorphisms produced by 13 EST-SSR primers were used to produce genetic similarity matrix for 80 genotypes. Dendrogram prepared from this genetic similarity matrix will be useful in selecting parents carrying diversity at drought specific loci.

Maize production is limited agronomically by the availability of water and nutrients during the growing season. Of these two limiting factors, water availability is predicted to increase in importance as climate change and the growing urban landscape continue to stress limited supplies of freshwater. Historically, efforts to breed maize for water-limited environments have been extensive; especially in the areas of root architecture and flowering physiology. As progress has been made and new traits have been discovered and selected for, the different responses to drought stress at specific developmental stages of the maize plant have been selected as a whole when drought tolerance is evaluated. Herein we attempt to define the characteristics of the maize drought response during different developmental stages of the maize plant that can be altered through plant breeding. Towards breeding for drought tolerance, 400 inbred lines from a diversity panel were amplified and sequenced at the ZmLOX4 and ZmLOX5 loci in an effort to characterize their linkage disequilibrium and genetic diversity. Understanding these characteristics is essential for an association mapping study that accompanies this project, searching for novel and natural allelic diversity to improve drought tolerance and aflatoxin resistance in maize. This study is among the first to investigate genetic diversity at important gene paralogs ZmLOX4 and ZmLOX5 believed to be highly conserved among all Eukaryotes. We show very little genetic diversity and very low linkage disequilibrium in these genes, but also identified one natural variant line with knocked out ZmLOX5, a variant line missing ZmLOX5, and five line variants with a duplication of ZmLOX5. Tajima's D test suggests that both ZmLOX4 and ZmLOX5 have both been under neutral selection. Further investigation of haplotype data revealed that ZmLOX12, a member of the ZmLOX family, showed strong LD that extends much further than expected in maize. Linkage disequilibrium patterns at these loci of interest are crucial to quantify for future candidate gene association mapping studies. Knockout and copy number variants of ZmLOX5, while not a surprising find, are under further investigation for crop improvement.

The aim of this study was cloning of wheat (Triticum aestivum L. cv. Bayraktar) Trehalose-6-phosphate synthase gene and examining of gene expression pattern of wheat seedlings in response to salt and drought stress conditions using Wheat GeneChip (Affymetrix). In this study, 10-days old wheat seedlings were subjected to the salt (350 mM NaCl) and drought stress (20% PEG) for 24 hours, then root and leaf tissues were used for wheat TPS gene cloning and microarray studies. RACE (Rapid Amplification of cDNA Ends) was used to determine cDNA sequence of wheat TPS gene, TaTPS. The ORF of TaTPS encodes a putative protein of 859 amino acids with a predicted molecular weight (MW) of 96.7 kDa and an isoelectric point (pI) of 5.97. Based on tblastx, TaTPS showed great similarity with other plants TPS genes. In root tissue, expression of TaTPS increased under drought stress while no change was observed under salt stress. In leaf tissue, both salt and drought treatments repressed the expression of TaTPS. Microarray study was used to monitor transcript abundance in salt and drought stressed wheat. Data analyses were determined by using GCOS 1.4 and GeneSpring GX10. The genes encoding ferritin, Lipid transfer protein, LEA/Dehydrin, early nodulin, cold regulated protein and germin like proteins were upregulated at least 10-fold under salt and drought stress conditions. In addition, salt and drought stresses induced the expression of genes identified as DREB, ERF, NAC, MYB, and HSF, suggesting existence of various transcriptional regulatory pathways under salt and drought stresses.

Drought is a major constraint for attaining economic yield in tree crops. As an initial step to understand molecular response to water-deficit-stress in trees, gene expression in response to water stress was quantified using real-time RT-PCR. The specific objectives established for this to were I. to identify and characterize the genes induced by drought stress in Aleppo pine (Pinus halepensis) and II to identify and quantify the differentially expressed genes in different populations of Loblolly pine (Pinus taeda.L) due to water deficit (chapter III). Results of these studies may be used to identify candidate genes for future breeding programs against water-deficit-stress.

Previous studies have suggested that advection from the Mexican Plateau (MP) may influence rainfall over Texas in spring and summer; generally air ascends over the cordillera and descends over the southern plains. The two mechanisms may link the northern Mexico drought to Texas drought. Observations and the Community Earth System Model are used in this study to describe the 2011 Texas-northern-Mexico drought and examine the role of the MP on the hydro-climate over the southern US, providing implications for the linkage between the MP and rainfall over Texas. A control run and three experimental runs were performed with prescribed sea surface temperatures and sea ice fractions. The results show that when the MP becomes dry, rainfall declines locally and downstream. During the spring, the dry air brought to Texas by prevailing westerly winds suppresses local convection; but dry air advection from the highlands has little influence on rainfall over Texas during the summer when Texas is no longer in the downstream areas. During the summer, a warmer MP draws moist air over the peripheral low elevation areas to the highlands; it bends the low-level jet towards the highlands and an anti-cyclonic flow anomaly forms over the southern US, which causes air to diverge and tends to reduce rainfall over the southern US. / text

Many water resources throughout the world are demonstrating changes in historic water levels. Potential reasons for these changes include climate shifts, anthropogenic alterations or basin urbanization. The focus of this research was threefold: 1) to determine the extent of spatio-temporal changes in regional precipitation patterns 2) to determine the statistical changes that occur in lakes with urbanizing watersheds and 3) to develop accurate prediction of trends and lake level return frequencies. To investigate rainfall patterns regionally, appropriate distributions, either gamma or generalized extreme value (GEV), were fitted to variables at a number of rainfall gages utilizing maximum likelihood estimation. The spatial distribution of rainfall variables was found to be quite homogenous within the region in terms of an average annual expectation. Furthermore, the temporal distribution of rainfall variables was found to be stationary with only one gage evidencing a significant trend. In order to study statistical changes of lake water surface levels in urbanizing watersheds, serial changes in time series parameters, autocorrelation and variance were evaluated and a regression model to estimate weekly lake level fluctuations was developed. The following general conclusions about lakes in urbanizing watersheds were reached: 1) The statistical structure of lake level time series is systematically altered and is related to the extent of urbanization 2) in the absence of other forcing mechanisms, autocorrelation and baseflow appear to decrease and 3) the presence of wetlands adjacent to lakes can offset the reduction in baseflow. In regards to the third objective, the direction and magnitude of trends in flood and drought stages were estimated and both long-term and short-term flood and drought stage return frequencies were predicted utilizing the generalized extreme value (GEV) distribution with time and starting stage covariates. All of the lakes researched evidenced either no trend or very small trends unlikely to significantly alter prediction of future flood or drought return levels. However, for all of the lakes, significant improvement in the prediction of extremes was obtained with the inclusion of starting lake stage as a covariate.

Climate models forecast lower and less frequent precipitation in the next 50 years. This is especially pronounced in the central United States, where Texas is expected to lose a week’s worth of rain every summer. Water availability is a primary driver of carbon flux in terrestrial ecosystems – controlling photosynthesis and organic matter decomposition. Thus, under proposed rainfall shifts, understanding the potential ecosystem response is key to predicting the future of terrestrial productivity. Terrestrial nutrient cycling is also driven by microbial saprotrophs, which are the chief decomposers of organic matter. Understanding the microbial response to rain shifts is key in predicting the ecosystem response. Research supports both microbial community specialization to local environment, and that the microbial communities may have the ability to rapidly acclimate to environmental change. To address this question of microbial response, we used a steep natural rainfall gradient along the Edwards Plateau in central Texas. The Edwards Plateau is an ideal field site in which to test these ideas because nearly identical grassland habitat and soils are found across its entirety, while mean annual precipitation ranges from 45 cm to 91 cm. To understand how soil microbial communities varied as a result of historical rainfall differences, we divided the gradient into four isoclines based on precipitation (46-56 cm, 56-66 cm, 66-76 cm, and 76-86 cm), and examined soil and soil microbial community characteristics at three sites in each isocline. We further used soils from the same sites for a reciprocal soil moisture experiment, where we asked how soil microbial communities responded to altered moisture conditions. Using a full factorial design, soils from each site in each isocline were exposed to one of four soil moisture treatments: soil moisture from the ‘home’ isocline and the three other ‘away’ isoclines. The moisture treatments were maintained for one year. Microbial respiration was measured at regular intervals throughout the experiment; fungal hyphal abundance and inorganic nitrogen were measured at the final harvest. The soils collected from the gradient decreased in both soil moisture and hyphal abundance from the wet to the dry end of the gradient, but there was no trend in inorganic nitrogen. In the reciprocal moisture experiment, microbial CO2 respiration was affected by both home isocline and soil moisture treatment. Drier sites had a narrower response to wetter treatments and did not achieve the same activity as wetter sites regardless of soil moisture treatment. In contrast, soils from the wettest isocline experienced severe reductions in activity with drying, with activity at the driest moisture treatment below that found in soils that were from the driest isocline. These patterns are consistent with some degree of local specialization, which may constrain the ability of microbial communities to rapidly acclimate to altered precipitation regimes. This experiment did not include immigration, however, and shifts in community composition in the presence of dispersal may be able to counteract local specialization. Given expected future increases in drought intensity microbial decomposition activity is likely to decrease and local specialization may create a lag in acclimation to the new condition. Thus, local specialization of microbial communities should be considered when predicting ecosystem responses to future climate change and their potential feedbacks to ecosystem productivity and carbon storage. / text

Upland cotton (Gossypium hirsutum) is cultivated in many contrasting production environments and is often subjected to a combination of abiotic stresses such as high temperature (heat) and water deficit (drought) stress. In the present dissertation, two recombinant inbred line populations were constructed from heat-tolerant and -susceptible parental lines and evaluated in multiple environments under the presence of two treatments, well-watered (heat stress) and water-limited in the presence of high temperature (combination of heat and drought stresses). We assessed two agronomic traits, seed cotton yield and lint yield, as well as six fiber traits, lint percent, micronaire, length, strength, uniformity, and elongation. Fiber traits had moderate to very high broad-sense heritabilities, while heritabilities of agronomic traits were lower for both populations in each irrigation regime. Correlations between traits were not effected by the irrigation regimes. A stability analysis across the range of environments tested demonstrated that high seed cotton yield performance and greater stability may play a role in tolerance to the combination of heat and drought stresses. Additionally, we constructed linkage maps for both recombinant inbred line populations and mapped QTL controlling variation all eight traits. A total of 138 QTL were identified across populations for the eight traits. Climate change in the form of rising temperatures and reduced water availability will increase the occurrence of the combination of heat and drought stresses in a farmer's field. Thus, current cotton breeding programs will need to focus on the development of cotton varieties tolerant to heat, drought, and the combination of the two.