Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 199-213). Also available on the World Wide Web.

This thesis deals with the negative interrelationship between climate fluctuation and cattle ranching during the 1880s. The focus is on three large ranches that were used as case studies on the Texas Panhandle. These ranches were selected because of their size, longevity, and the number of primary documents that were available at the Panhandle Plains Museum and Archive in Canyon, Texas. The temporal focus is from 1880 to 1890. The primary documents that have been examined are letters from ranchers to the Capitol Syndicates that owned the ranch and the financial documents of each ranch. Scientific journals that examined grassland ecology, animal ecology, and climate were used in conjunction with the primary documents. The combination of these sources led to a nuanced reinterpretation of a cattle disaster from the 1880s. The disaster was a massive loss of stock through a series of extremely cold winters and a drought that lasted several years. In the wake of this disaster, through the use of technology, these ranches were able to recover and increase their stock numbers beyond what they were prior to the years dominated by stock losses and low cattle prices.

This thesis deals with the negative interrelationship between climate fluctuation and cattle ranching during the 1880s. The focus is on three large ranches that were used as case studies on the Texas Panhandle. These ranches were selected because of their size, longevity, and the number of primary documents that were available at the Panhandle Plains Museum and Archive in Canyon, Texas. The temporal focus is from 1880 to 1890. The primary documents that have been examined are letters from ranchers to the Capitol Syndicates that owned the ranch and the financial documents of each ranch. Scientific journals that examined grassland ecology, animal ecology, and climate were used in conjunction with the primary documents. The combination of these sources led to a nuanced reinterpretation of a cattle disaster from the 1880s. The disaster was a massive loss of stock through a series of extremely cold winters and a drought that lasted several years. In the wake of this disaster, through the use of technology, these ranches were able to recover and increase their stock numbers beyond what they were prior to the years dominated by stock losses and low cattle prices.

The relationship between the satellite-based Vegetation Condition Index (VCI) and frequently used agricultural drought indices like Palmer Drought Severity Index, Palmer’s Z-index, Standard Precipitation Index, percent normal and deciles was evaluated using a comparative correlation analysis. These indices were compared at the county level for all 254 Texas counties for the growing-season months (March to August) using monthly data from 1982-1999. The evaluation revealed that the VCI was most strongly correlated with the 6-month SPI and the PDSI. This suggests that the VCI is most similar to drought indices that account for antecedent moisture conditions. There was also significant spatial variability in the magnitude of the correlations between the VCI and the drought indices. The reasons for this variability were explored by utilizing additional data such as irrigation, prevalent landuse/landcover, water table depth, soil moisture levels and soil hydrologic/hydraulic properties. The results demonstrated that mean annual precipitation, soil moisture, landuse/landcover, and depth of the water table accounted for a significant amount of the spatial variability (explaining more than 75% of the variance) in the relationship between the VCI and traditional drought indices.

Perennial grass vegetation dynamics of heavy grazing, moderate grazing and ungrazed treatments were analyzed during two extreme drought events: the drought of 1951 to 1956 and the drought events centered on the year 2000. Analysis of each drought event from weather records and Palmer Drought Severity Index values showed that the intensity, duration and pattern of each drought event were structurally unique. Grazing intensity was the primary driver of perennial grass species composition and community structure both during and between each drought event. Total basal area for each drought event was driven primarily by variation in precipitation pattern. Basal area per plant dynamics were significantly influenced by grazing intensity while plant density was driven by both precipitation and grazing intensity. Topo-edaphic variation significantly influenced the persistence and distribution of perennial grass species during an extreme drought event centered on the year 2000. The presence of large or abundant surface rock features facilitated the survival of perennial grasses during this drought event by creating a positive soil microenvironment. Sites with large surface rock features acted as drought refugia for perennial grass populations. Sites with abundant surface rock features had 10 times greater perennial grass basal area and 5 times greater plant density than sites with few surface rock features. Grazing intensity was the primary driver of species composition and community structure within both refugia and non-refugia sites. Grazing intensity had no effect on perennial grass basal area. However, grazed treatments had two times greater perennial grass density than non-grazed treatments. Species response to grazing intensity and surface rock cover was individualistic. Grazing response groups (intolerant, intermediate, and tolerant) separated along a gradient of surface rock cover and grazing intensity. Abundant surface rock features act as refugia for perennial grasses by facilitating their persistence during extreme drought events on the Edwards Plateau.

From June to August 2011, Texas experienced the hottest summer ever recorded in the history of the United States, and the state suffered a water shortage that made its vulnerability to drought painfully plain. This disaster sparked new interest in methods of defining drought severity, especially with regard to the variation of soil moisture levels. This thesis assesses the suitability of information from the North American Land Data Assimilation System (NLDAS), an assemblage of land surface models forced with observations data, for quantifying soil moisture levels in Texas. The potential for combining NLDAS data with the Soil Survey Geographic (SSURGO) Database’s available water capacity data is explored. It is discovered that because NLDAS is a hydrological model and SSURGO an agricultural dataset, they employ different definitions of soil moisture storage. Moreover, the temporal variation of soil moisture levels in the SSURGO polygons cannot be inferred from NLDAS data due to the vastly different spatial scales of the two datasets. A relative measure of soil saturation from 0–100% is developed instead and determined to be a more useful indicator of drought than the soil moisture level itself. Calculated solely from NLDAS data, it is used to map the severity of drought in Texas, with the results displayed at the county scale. The temporal variation in soil moisture storage across the state is compared with variations in the gravity anomaly measured by NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites and variations in Texas surface water reservoir levels, both of which are physical measurements of water storage changes. This analysis suggests that the NLDAS data, which is derived from a land surface model, accurately describes subsurface moisture variations. Also, the GRACE gravity anomaly data reveals that during the 2011 drought, the total water storage in Texas was approximately 100 cubic kilometers less than normal. NLDAS data indicates that more than 50% of this deficit was due to losses from the top one meter of the state’s soils. / text

The context of megadrought, drought more severe than any we have experienced over the past 100 years, is assessed in this dissertation. A set of new climate reconstructions including drought, dustiness, and temperature from the south San Juan Mountains in southern Colorado is presented here and provides unforeseen insights into these unusual events. The global context of megadroughts is also analyzed using a network of reconstructions. The new drought record is from bristlecone tree-rings, spans the last 2000 years, and shows two periods with anomalous aridity and drought in the south San Juan Mountains. The later period corresponds with well-characterized medieval climate anomaly (MCA; 900-1400 AD) aridity in southwestern North America (henceforth the Southwest). The earlier interval coincides with the Roman Period (1-400 AD). A severe drought with, almost 50 consecutive years of below average tree-growth, occurs in the middle of the Roman Period during the 2nd century AD. Assessment of Roman and MCA droughts in the context of global climate reconstructions reveals that similar hemisphere scale circulation patterns during both intervals might have contributed to severe aridity in the Southwest. Next relationships between droughts and pluvials in western North America (henceforth the West) and global sea surface temperature (SST) patterns over the last 1100 years are examined. Several methods are used including teleconnection patterns imbedded in tree-ring reconstructed drought maps, and a global network of SST reconstructions. Teleconnection patterns during droughts and pluvials suggest that megadroughts and pluvials were likely forced in part by sequences of anomalous years in the Pacific and Atlantic Ocean, but the analyses also reveals contradictory results that may require new ways of understanding the relationship between SSTs and drought on long timescales. Next, returning to the south San Juan Mountains, we developed a new dust reconstruction from a lake sediment core. The reconstruction illustrates that dustiness has been an important component of Southwestern climate over the past 2941 years. The record shows high dust deposition in the past especially around 900 BC and during the MCA. High dust deposition before recent land use changes suggests that megadroughts or associated periods of aridity were widespread and severe enough to mobilize dust, perhaps resulting in further reductions to mountain snowpack and stream flow. Finally, a new biomarker based temperature reconstruction is presented. The reconstruction spans the last 2000 years and shows that the warmest temperatures during that interval occurred during the Roman Period and the MCA. The record suggests these periods were warmer than today, indicating the San Juan Mountains are a sensitive region to temperature change. Both past warm periods coincide with anomalous drought and dustiness, suggesting that temperature and dust may have acted as megadrought enhancing feedbacks. In summary, this dissertation helps characterize the timing and causes of southwest North American Megadroughts over the past 2000 years; separately addressing changes in moisture balance, dustiness, temperature, hemispheric circulation, and sea surface temperature forcing patterns during these unusual events.

This dissertation has two primary objectives. First, through an analysis of empirical data, it presents a systematic, in-depth analysis of how rural populations react and adjust to adversity within specific socio-economic and institutional contexts. The analysis applies a vulnerability framework to understand the complex relationships between households, communities, and larger environmental, socio-economic, and political factors and how they influence drought impacts on the population. Using a combination of quantitative and qualitative data to look at issues of overall well-being, resource access, and livelihood and risk management strategies, the results provide insights into why most households are unable to successfully mitigate the impacts of drought. The analytical framework also provides a mechanism for making policy-relevant recommendations. In this vein, the dissertation explores the need for a new approach to the status quo of public policy making and presents an applied model for participatory planning to reduce drought vulnerability in Ceará. The pilot program, Projeto MAPLAN, is an effort, based on an empirical understanding of the public and private sides of vulnerability, to redefine the way that politics as usual are carried out. It challenges the way in which decisions are made by stimulating public participation and providing tools for accountability. On the public side it works to institutionalize effective participation through citizen input and governmental recognition of that input. On the private side the model works to increase the availability of resources and improve access to resources in order to expand the range of opportunities and strategies and to help households flourish in a semi-arid region.

Cottonwoods (Populus sp.) and willows (Salix sp.) are generally limited to riparian landscapes in semi-arid regions of western North America. Water availability is a major determining factor for the establishment, growth and survival of these plants. Willows generally occur closer to the stream and at lower elevations than cottonwoods, suggesting reduced drought tolerance and increased flood tolerance. In the present thesis project, three related studies were conducted to investigate this hypothesis. Firstly, tolerable rates of water table decline and the impacts of the corresponding drought stress were investigated by growing cottonwoods and willows under water table decline rates from 0 to 12 cm/d. Willow saplings responded similarly to cottonwood saplings, but willow seedlings were more vulnerable than cottonwood seedlings to rapid rates of water table decline. In the second study, will saplings tolerated elevated water tables of 0 to 7.5 cm below substrate surface and the resulting flood stress for 152 days slightly better than cottonwood saplings. Finally, mature cottonwoods along Willow Creek, Alberta experienced water table decline from 1996 to 1998 due to water pumping in a nearby gravel pit; the water table recovered in 1999. The cottownwoods displayed physiological changes indicating drought stress in 1998 and recovered following restoration of the water table. This confirmed the cottonwoods' reliance on the water table as their primary moisture source. These studies indicate that the spatial separation of willows and cottonwoods may be particularly related to reduced drought tolerance of willows and these display only slightly increased flood tolerance of willos and these display only slightly increased flood tolerances. The studies confirm that both willows and cottonwoods are physiologically dependent on a sufficient riparian water table. / 85 leaves : ill. ; 28 cm.

The Winnipeg River Drainage Basin (WRDB), located in the boreal forest region of Canada, is a pivotal region of focus for the assessment of water availability to determine susceptibility to drought in the past. To date, there have been relatively few paleolimnological studies focusing on how lake levels have changed in the past and whether these changes have been synchronous in the WRDB. This study investigates temporal patterns in effective moisture from Little Raleigh Lake over the last two millennia. Analyses are based on diatoms from two near-shore sediment cores from different locations and water depth in Little Raleigh Lake. Changes in diatom assemblages are used to reconstruct quantitative estimates of effective moisture in the past through the calibration of a diatom-inferred depth model developed from diatom assemblages in surficial sediments along a depth transect in Little Raleigh Lake. Declines of ~1-3m occurred during the late Holocene, with prolonged periods of aridity consistent with the timing of the Medieval Climate Anamoly (~950-1250AD) and the Little Ice Age (~1650-1750AD). The nearshore core retrieved closer to the present-day ecotone between the benthic and planktonic diatom assemblages was more sensitive to tracking water level changes in the lake than the deeper core. Conditions during the last two millennia can be used for the assessment of water availability in the past, and may offer insight on future conditions under increasing temperatures. / Thesis (Master, Biology) -- Queen's University, 2011-07-29 17:09:49.155