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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Drought over the past century in Texas and New Mexico: reducing inhomogeneities in long-term climate records via statistical methods to study drought

McRoberts, Douglas Brent 10 October 2008 (has links)
This research looks at the past century of Texas and New Mexico climate in order to create datasets sufficient for documenting climatic variations. Inhomogeneities in climate records are defined as variations in climatic records caused by factors other than weather and climate. While there are indirect methodologies for inferring climate records such as tree rings and ice cores, it is the instrumental network that constitutes the most spatially and temporally complete record of land surface climate since the onset of the Industrial Revolution. A statistical method by Sun and Peterson (2005a) called Inverse Weighting of Square Distance (IWSD) will be used to reduce the inhomogeneities in climate records. The National Weather Service Cooperative Observer Program (COOP) network of stations will be used for this analysis. A subset of the extensive COOP network, called the United States Historical Climate Network (USHCN), will be used as a foundation for this study. The analysis and resulting datasets from this climatic study show precipitation trends and periods of drought and will be useful for decisions regarding future policies on drought. The result of the interpolation process was the creation of several COOP and USHCN datasets. Several of the datasets were investigated to determine the spatial characteristics of precipitation over the 20th century in Texas and New Mexico. The datasets are in good agreement that the most severe drought period of the 20th century in Texas and New Mexico was in the 1950s. The frequency of pluvial periods was higher toward the end of the 20th century, with most USHCN stations showing an increasing trend when a linear regression analysis was done on each station's precipitation data.
2

The impact of soil moisture deficit on the interactions between oilseed rape and insect herbivores

Burgess, Adam Jason January 1996 (has links)
No description available.
3

Physiological applications for determining water use efficiency among cotton genotypes

Bynum, Joshua Brian 15 May 2009 (has links)
Drought stress can substantially alter plant metabolism by decreasing plant growth and photosynthesis. The lack of rapid and reliable screening criteria and measurement techniques for determining water use efficiency (WUE) of crop plants has greatly restricted progress in this critical area of crop improvement. In grain sorghum (Sorghum bicolor L.), WUE was associated with the transpiration ratio [CO2 assimilation (A) / transpiration rate (E), A:E] from leaf gas exchange measurements. Research is needed to identify drought effects on plant productivity and to exploit the use of this knowledge in breeding and agronomic efforts. Therefore, the objectives of this study were to determine if differences in A:E and other physiological parameters existed between two selected cotton (Gossypium hirsutum L.) genotypes and to evaluate the response of cotton genotypes experiencing water stress at two different growth stages on biomass production and yield. Two experiments were conducted using two cotton genotypes differing in drought tolerance. Each experiment was repeated three times in a randomized complete block design with six replications. In Experiment I, the water stress treatment was induced by withholding water when the plants reached the 4-node growth stage. The water stress treatment in Experiment II was imposed at early bloom. Gas exchange and chlorophyll fluorescence measurements were collected during dry-down and recovery periods to determine water stress effects on plant physiology. Biomass was partitioned following the recovery period, to examine phenotypic responses of plants exposed to water stress. The results of these experiments indicate that A:E is significantly increased as leaf water potential (ψL) decreases with no differences in A:E between the two genotypes. Gas exchange measurements showed significant decreases with declining ψL and significant increases upon re-watering; yet, no differences were observed between the two genotypes. Chlorophyll fluorescence was not different between genotypes in either light- or dark-adapted leaves. In Experiment I TAM 89E-51 had a significantly greater seedcotton yield; however, in Experiment II TAMCOT 22 had the greater yield. These experiments suggest that the effects of water stress on cotton are a function of the intensity of the stress and the growth stage in which the stress is experienced.
4

Physiological and genetic control of water stress tolerance in zoysiagrass

Dewey, Daniel Wade 12 April 2006 (has links)
Significant cultivar difference in many water stress responses of zoysiagrass (Zoysia japonica (Steud.) and Zoysia matrella (L.) Merr.) are shown in this study. Of the four cultivars, Palisades was the most water stress tolerant, had the most negative turgor loss point, and leaf rolled after loss of full turgor pressure. On the other end of the spectrum, Diamond was the least water stress tolerant, had the lowest full turgor pressure, the least negative turgor loss point, and leaf rolled at full turgor. Differences between Diamond, Cavalier, Palisades, and DALZ 8504 in leaf rolling, loss of full turgor, water release curve parameters, root characteristics and gene expression make zoysiagrass a prime candidate for further investigation into the mechanisms of water stress avoidance/tolerance. Enhanced antioxidant activity and stomatal control, along with root characteristics, most likely explain the cultivar difference in water stress tolerance of zoysiagrass. Palisades and DALZ 8504 maintained full turgor for significantly longer than Diamond and Cavalier, which may be associated with root characteristics and/or enhanced stomatal control as only those two cultivars showed enhanced expression of a stomatal control gene (phospholipase D). The apparent response (most apparent in turgid weight/dry weight ratios (TWDW)) of well watered plants to water stressed neighbor plants will likely be the most novel finding of this study. Well watered zoysiagrass and Kentucky bluegrass responded to water stressed neighbors by reducing TWDW. Significant increases in gene expression of a systemin degrading enzyme and of an integral membrane protein (signal receptor) were also observed in well watered plants. Results from this study indicate that this phenomenon is occurring and expose a dearth in scientific understanding that must be filled. Improving water stress tolerance through breeding for parameters like those discussed in this paper (delayed leaf rolling or loss of full turgor, enhanced stomatal control, enhanced antioxidant activity, deep rooting characteristics, etc.) may very likely produce turfgrasses that can survive and maintain desired aesthetic qualities using significantly less water.
5

On the edge of the big dry : running out of water in West Texas / Running out of water in West Texas

Barton, Ryland Derek 27 February 2012 (has links)
In the wake of the 2011 drought, finding water is one of the most pressing issues that face West Texas cities. The city of San Angelo finds itself in the unique position of being a West Texas town with several lakes, but now only has 22 months' worth of water left. In an attempt to bring more water to the drought-stricken population, the city is constructing a $120 million pipeline to pump water 65 miles from the Hickory Aquifer -- widely known to have high levels of radium that makes the water radioactive. This report, and the two accompanying audio stories, examines the implications of the move, which San Angeloans hope will secure the city’s hydrological, economic, and political future. / text
6

An assessment of the environmental impact of drought on waterfowl in agro-Manitoba and recommendations for mitigation measures

Semchuk, Ben January 1982 (has links)
Drought is a recurring climatic phenomenon of the northern Great Plains which include most of Agro-Manitoba. Historical and archaeological evidence indicates that cyclical dry periods have been occurring since ancient times and will continue into the future. Droughts generally have an adverse impact on wildlife and wildlife habitat. In the case of waterfowl, cyclical droughts have both positive and negative environmental impacts. Prairie dry cycles have the effect of rejuvenating wetlands and improving them as waterfowl habitat. Waterfowl have developed an equilibrium with alternating wet and dry prairie cycles, after thousands of years of evolution. Stable waters in the northern latitudes provide a place for resident and drought-displaced waterfowl to await the return of wet conditions on the prairies. Waterfowl can explosively reproduce their numbers on the fertile prairies during a wet cycle. On the negative side, droughts cause the decline of the continental populations of waterfowl because of adverse nesting conditions. Reduced populations result in reduced harvest opportunities and an economic loss. The equilibrium of waterfowl with alternating wet and dry prairie cycles has been altered by the introduction of large-scale agriculture on the prairies. Agricultural activities are responsible for the progressive elimination of wetlands which are vital for waterfowl to repopulate themselves during wet cycles. The federal grain quota is the chief policy acting against wetlands preservation. It is only recently that the true economic valuation of wildlife has been appreciated. Economists have determined methods of placing monetary valuations on wildlife. The indirect travel cost method is applicable to waterfowl at specific sites in Agro-Manitoba. Mitigation measures for the the negative environmental impacts of drought on waterfowl depend upon government policies that support wetlands preservation. There are a multitude of ways to preserve and enhance wetlands. Agricultural practices can be modified and adapted to achieve wetlands preservation.
7

The international politics of famine relief operations in Ethiopia : a case study of the 1984-86 famine relief operations

Bello, Ghaji Ismaila January 1990 (has links)
This thesis is a study of the international relief assistance to Ethiopia during the 1984-86 famine. It begins by examining the country's glorious past vis-a-vis its present international status. In Part One, the underlying causes of the famine are discussed to provide a background to the subsequent analysis of the international relief effort. Also discussed, is the role of the international media in alerting public opinion and successfully transforming the famine into an issue of international concern. In Part Two, the responses of the various actors are analysed: in particular the bilateral response of Ethiopia's political allies and her opponents; of the Western non-governmental organizations (NGOs) and the role of the United Nations in coordinating the international relief effort at the multilateral level. Part Three (Chapter Eight), tests the theoretical assumptions outlined at the beginning of the thesis. With regard to the first, namely the relative importance of opponents and allies, the study concludes Ethiopia's political opponents were more responsive to her appeal for emergency relief than her allies. With regard to the second, namely the role of the NGOs the conclusion is that these organizations played the most important role in shaping the international response to the emergency. Chapter Nine summarizes our general conclusions.
8

Understanding Flash Drought Spatial Extent, Duration, and Meteorological Drivers

Kaniewski, Connie 01 September 2021 (has links)
Drought is conventionally known as a slow-developing natural hazard. In recent years, a subset of drought events characterized by rapid onset has been identified and deemed “flash” droughts. These flash droughts can result in rapid soil drying and rapid vegetation degradation making them damaging to agriculture and the economy, so it is essential to develop reliable early warning systems for flash drought events. This study aims to compare the climatology between flash and non-flash droughts across the Contiguous United States (CONUS) and regionally to identify key differences in the drought types to improve early warning. Flash drought is defined as a two- or more category degradation in the U.S. Drought Monitor (USDM) in 4 weeks or less. Potential evapotranspiration (PET), vapor pressure deficit (VPD), maximum temperature (Tmax), and minimum temperature (Tmin) from the Gridded Surface Meteorological Dataset (gridMET) were also analyzed for flash and non-flash drought. It was found that using this definition of flash drought, flash droughts are up to 70% more likely to occur than non-flash droughts over all of the CONUS except the west coast. The South and Southwest regions are more likely to have more frequent and longer flash drought events than the Northwest and Plains regions. This study concludes that PET and VPD are the most reliable variables for differentiating between a flash and non-flash drought event. Furthermore, flash drought is most prevalent and will be the most difficult to predict in the South and Southwest regions and easier to predict in the Northwest and Plains. Also, using a flash drought definition of a drop in two or more categories in the USDM may be too lenient. A narrower flash drought definition, such as a drop in two categories over a two- or three-week period, may be more reflective of the more damaging nature of flash drought events.
9

Advanced Analysis of the Responses of Cotton Genotypes Growing Under Water Stress

Maeda, Murilo Minekawa 1985- 14 March 2013 (has links)
The ever-growing world population raises the concern and necessity of rational use and distribution of limited water resources. Water deficit is the single most dominant abiotic factor limiting cotton (Gossypium hirsutum L.) yield in drought-prone Texas croplands. Characterizing plant traits conferring drought tolerance to cotton genotypes and then transferring this information back to breeders and geneticists have the potential of significantly increasing and stabilizing production statewide. Although a plethora of physiological studies have been conducted and have demonstrated that drought tolerance in plants is likely to be conferred by a combination of plant traits rather than a single trait, this knowledge has not translated into improved breeding lines. Experiments were conducted in 2010 and 2011 in the Drought Tolerance Laboratory (Texas AgriLife Research and Extension Center in Corpus Christi, TX) to analyze the responses of cotton genotypes to different levels of water stress. This facility is equipped with computerized systems capable of continuously monitoring whole-plant water use as well as several environmental parameters. Sixteen cotton genotypes were provided by Monsanto Co. and the Texas AgriLife Cotton Improvement Programs at College Station and Lubbock. Seeds were pre-germinated in wet paper towels and then hand planted in large pots previously filled with fritted clay. A total of 3 and 8 (2010 and 2011, respectively) pots containing plants of each genotype were permanently placed on micro-lysimeters for continuous measurement of water use. Water regimes were imposed in 2010 (well-watered and water-stressed), and 2011 (water-stressed) when plants reached the early-flowering stage and were carried until plants reached maturity (100% open bolls). Data collected showed that genotypes have very distinct water use patterns. The water stress treatment imposed on the test plants negatively affected plant growth that was indicated by a lower plant height, total number of leaves, and main-stem nodes of stressed plants when contrasted to their well-watered counterparts. Stomatal density was remarkably different among genotypes and a higher density was found on the abaxial (lower) leaf surface for all genotypes studied. Root dry mass production had different responses depending upon the severity of the water stress. Highest root dry mass was observed when plants were exposed to a mild stress and lowest when a more severe water restriction was imposed.
10

Developing a flash drought indicator for the US Great Plains

Yang, Ze, active 2013 30 October 2013 (has links)
Flash droughts refer to those droughts that intensify rapidly in spring and summer, coupled with a strong increase in summer extreme temperatures, such as those that occurred over Texas in 2011 and the Great Plains in 2012. Climate models failed to predict these flash droughts in 2011 and 2012 and are ambiguous in projecting their future changes, largely because of models’ weaknesses in predicting summer rainfall and soil moisture feedbacks. In contrast, climate models are more reliable in simulating changes of large‐scale circulation and temperatures during winter and spring seasons. Thus, we developed and tested a physical climate indicator of the risk of “flash” droughts in summer by using the large-scale circulation and land surface conditions in winter and spring based on observed relationships between these conditions and their underlying physical mechanisms established by previous observational studies and numerical model simulations. My master research focuses on the spatial distribution of this indicator globally to see how broadly it could be applied. We also compare the different factors to see which one is the dominant contributor to drought in different area. We find that the indicator performs well at capturing the development and termination of a drought. There is much opportunity to develop and improve the indicator further. / text

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