Hurricanes are the leading cause of economic loss in the United States, and recent studies have shown that they have increased in intensity. The growth of population and wealth to coastal regions has exacerbated catastrophic losses. The purpose of this study is to examine the role of three modes of natural climate variability as well as hurricane intensification on destructiveness along the Gulf Coast. The study utilized R programming software to create raster grids and evaluate spatial and temporal relationships between intensification, intensity, sea surface temperatures and destructiveness. Destructiveness was synthesized using the Pielke Landsea 2018 (PL18) normalized losses dataset. The principal findings revealed that the Atlantic Multidecadal Oscillation (AMO) has the greatest influence on hurricane intensification and associated damages. The study offers a contribution to research on hurricane intensification and destructiveness associated with natural climate variability and urges stakeholders to dedicate funds for mitigation measures to reduce the vulnerability to Gulf Coast counties.

The hydrology of southwestern British Columbia is influenced by the region’s mountainous topography and climate oscillations generated from the Pacific Ocean. While much of the region is characterized as a temperate rainforest, recent summers are defined by record-breaking droughts that focus attention on the threat to regional water supply security likely to accompany future climate changes. The limited length and distribution of hydrological records in southwestern British Columbia provide poor context for resource managers tasked with developing policy and water management strategies. The purpose of the dissertation was to describe long-term variability in several key hydroclimatic variables and hydroecological interactions that may be used in updated water resource policy and management strategies. Specifically, the research focused on developing long-term proxy records of April 1 snow water equivalent (SWE), summer streamflow, spring lake levels, and salmon abundance from tree ring records. A secondary goal of the dissertation was to identify the role and influence of several key climate oscillations on regional long-term hydroclimatic and ecological variability. Freshet contributions from melting snow are critical for sustained summer streamflow in southwestern British Columbia. Even so, few manual snow survey stations exist within the region are of sufficient length to understand the full range of natural SWE variability. Long-term April 1 SWE records were constructed by establishing statistical relationships with the radial growth of high-elevation trees and April 1 SWE records. Explaining 51% and 73% of the total variance in the instrumental SWE records in coastal and continental settings, the reconstructions provide high-resolution descriptions of April 1 SWE over the past three centuries and help position the remainder of the dissertation. Negative phases of the Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO) were shown to strongly influence April 1 SWE totals. Both reconstructions illustrate repeated step-changes in April 1 SWE during the last 300 years and show that coastal areas may be more sensitive to annual variability than snowpack that accumulates in more continental locations. Water shortages in the Metro Vancouver area in recent summers are linked to low total winter snowpack and early spring melt. Dendrohydrological analysis of dry-season streamflow was conducted to determine if the instrumental range has been underestimated over the past several centuries. A regionalized record of July-August streamflow for the Capilano and Seymour watersheds, which supply the Metro Vancouver area, was modelled from present to 1711using tree-rings. Explaining 54% of total variance over the instrumental period, the models show that below-average streamflow events are becoming more frequent. When compared to those characterizing the past 300 years, streamflow totals from 1977 to present have consistently fallen well-below the average long-term discharge. Further analyses indicated that negative ENSO and PDO conditions strongly influenced July-August runoff trends since 1711, as have climate regimes related to the Pacific North American pattern (PNA). The increased frequency in recent years of reduced summer runoff in southwestern British Columbia has led many communities to rely on natural and dammed reservoirs to supplement their water needs. Where communities rely on natural lakes, this dependence may have socioeconomic consequences if lake levels fall below those necessary to supply built infrastructure. Unfortunately, there are few lake level records in southwestern British Columbia and none of sufficient duration to understand the full range of variability in natural lake systems. Harrison Lake is the only natural lake with a lake level record exceeding 50 years. Using the average April water level dataset, a dendrohydrological model was constructed that explained 49.5% of total variance. The model was used to reconstruct a proxy record of April water levels spanning the interval from 1711 to 1980. Averaging 9.37 m in depth, lake levels in Harrison Lake ranged from 8.9 to 10.0 m over the past 300 years. These variations were shown to be statistically associated with negative and positive phases of ENSO and positive phases of PDO. April water levels in Harrison Lake have been, on average, 0.13 m lower since the mid-1930s compared to the previous 200 years. This reduction in storage capacity amounts to a loss of almost 300-million litres of stored water since the start of instrumental records. Salmon play a vital economic, cultural, and social role in many southwestern British Columbia communities. There is concern that salmon populations in the region are under threat, as changing climates alter and impact their spawning habitat. While various lines of research have sought to determine the response of salmon to these changing conditions, population records that extend only to 1951 hinder a complete understanding of the impacts. Two dendroecological models were constructed to provide a longer-term perspective of regional salmon-climate relationships. Explaining 48.2% and 48.9% of variance in observed Chinook and Coho salmon abundance since 1951, the models were used to construct proxy escapement records extending to the 1700s. Spectral analysis revealed that the reconstructions account for generational life histories and that low-frequency climate variability was associated with fluctuations in abundance. Both the Chinook and the Coho reconstructions show phase dependent relationships to climate oscillations generated from the Pacific Ocean. The Coho record is strongly linked to negative winter and spring ENSO, while the Chinook record was shown to be associated with negative PDO conditions. The identified relationships to teleconnections generated in the Pacific Ocean to our record indicates that both species are sensitive to oceanic interactions prior to entering natal habitats. Taken together, the reconstructions illustrate that the observational record encompasses a period of lower-than-average abundance and that neither accounts for the full range of variability in annual abundance when considered over the past three centuries. The proxy tree-ring records presented in this dissertation provide new information about climate-water resource relationships in southwestern British Columbia. Significant phase-dependent associations, especially to negative phases of the PDO and ENSO, were shown to exert long-term influences on the state of several critical hydroclimatic variables over the last 300 years. Additionally, the research illustrates that over the instrumental period, both streamflow and lake volumes in the region have consistently remained below those characterizing the previous two to three centuries. These findings are of direct use to resource managers tasked with developing new policy and strategies under present and future climate change, in that they offer singular insights into the full range of natural hydroclimatic variability in southwestern British Columbia. / Graduate

Dendroclimatological research along a geographical gradient is important to understanding both spatial and temporal characteristics of climate influences on tree growth. In this study, three tree-ring width chronologies, obtained from field collection and previous research, were used to represent tree growth along a longitudinal transect from coast to inland in the southeastern U.S.: Hope Mills, located at the Atlantic Coastal Plain; Linville Mountain, located on the eastern side of the Appalachian Mountains; and Gold Mine Trail, located on the western side of the Appalachians. The variations of ring width indices in chronologies reflect extreme climatic events such as severe droughts or cold periods. Correlation and response function analyses were used to examine the climate-tree growth relationship at three sites. The temporal stationarity of climate signals was tested using moving interval analysis in DENDROCLIM2002. Winter temperature was the limiting climate factor for the western mountain site, while moisture was more important for tree growth in the eastern mountain and coastal area sites. However, all significant climate signals found in the trees were not stable over time. The tendency of a shift from precipitation signal to temperature signal is notable around the mid-20th century. Winter North Atlantic Oscillation (NAO) had positive correlations with radial growth at the two mountain sites, which might explain the winter temperature response by trees. The Atlantic Multidecadal Oscillation (AMO) showed an annual feature of associations with growth, and the multidecadal duration of significant correlations was also apparent. The Pacific-related Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO) also tended to influence tree growth. Along the coastal-inland transect, gradient features of climate oscillation signals did exist. Relationships changed with phase changes of the oscillations. Land-sea boundaries and high mountains may determine the climate response patterns in the Southeast. Other factors such as microenvironment, human disturbance, and biological reaction of trees to climate change also have influence. It is not reliable to use the composite chronology to study the effect of climate oscillations for the Southeast region. In the future, a large number of sample sites will be necessary to more extensively study the regional climate-tree growth relationship.