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The Southeast United States during summer and fall is often affected by droughts and tropical cyclones. Both phenomena rank among the most expensive of natural hazards, although droughts are not as feared by the public as hurricanes. When a tropical cyclone causes a pendulum swing from drought to wet conditions, it is known as a “drought-busting tropical cyclone.” The majority of the research related to drought busting tropical cyclones investigates only the storms during their tropical cyclone phase, which covers the southeastern states that have boundaries adjacent to the Atlantic Ocean. An unanswered question from this literature is whether or not these findings apply to the interior southeastern states that have no ocean boundaries, where there is an increase in the probability of a drought-busting tropical cyclone transitioning to an extra-tropical cyclone. This thesis research attempts to determine the impact of drought-busting cyclones on the states of Kentucky and Tennessee. Research findings in this thesis revealed that droughts occur more frequently in the eastern climate divisions of the study area, 2-3 tropical cyclones affect the study area each year, and 6% of warm-season precipitation comes from tropical cyclones or their remnants. Chi-Square analysis and Kruskal-Wallis tests suggest that the Atlantic Multidecadal Oscillation (AMO) has statistically significant relationships with drought frequency, tropical cyclone precipitation, and extra-tropical cyclone precipitation in several climate divisions. While the literature argues that drought-busting tropical cyclones are common in coastal locations, they were found to be rare in Kentucky and Tennessee.

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The occurrence of wildfire is influenced by a suite of factors ranging from "top-down" influences (e. g., climate) to "bottom-up" localized influences (e. g., ignitions, fuels, and land use). We carried out the first broad-scale assessment of wildland fire patterns in northern Mexico to assess the relative influence of top-down and bottom-up drivers of fire in a region where frequent fire regimes continued well into the 20th century. Using a network of 67 sites, we assessed (1) fire synchrony and the scales at which synchrony is evident, (2) climate drivers of fire, and (3) asynchrony in fire regime changes. We found high fire synchrony across northern Mexico between 1750 and 2008, with synchrony highest at distances < 400 km. Climate oscillations, especially El Nino-Southern Oscillation, were important drivers of fire synchrony. However, bottom-up factors modified fire occurrence at smaller spatial scales, with variable local influence on the timing of abrupt, unusually long fire-free periods starting between 1887 and 1979 CE. Thirty sites lacked these fire-free periods. In contrast to the neighboring southwestern United States, many ecosystems in northern Mexico maintain frequent fire regimes and intact fire-climate relationships that are useful in understanding climate influences on disturbance across scales of space and time.

A variety of anthropomorphic and environmental stresses are threatening the existence of all seven species of sea turtles. There is growing evidence that alterations in surface waters and sediment temperatures are negatively impacting reproductive success of loggerhead sea turtles (Caretta caretta). Fluctuations in water temperature associated with localized climate oscillations heavily alter the food web dynamics of the ocean. Feeding conditions are expected to be a critical factor in determining body mass and productivity for breeding seasons. An increase in regional temperatures could lead to prolonged reduction in food sources, as well as reduced nesting and recruitment. Loggerhead sea turtle nesting data from 1995-2011 werre compared with the average yearly North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO) which are important climatic events impacting the SST in the Atlantic Ocean. Because El Niño Southern Oscillation (ENSO) is a global event, it was proposed that turtles in the Atlantic may follow a similar trend. ENSO was quantified using Oceanic Nino Index (ONI). Analysis of loggerhead sea turtle nest frequencies from the years 1995-2011 in comparison to seasonal climate changes showed a significant inverse relationship between the detrended loggerhead nests and average yearly NAO when lagged two years, suggesting loggerheads may spend years prior breeding obtaining optimum body mass to increase successful reproduction. The detrended nesting data showed a tendency toward higher occurrence of nests during La Niña years while nest frequencies decreased during El Niño year; when the yearly detrended loggerhead nesting data was compared with the average yearly ONI; showing a significant inverse relationship without a lag. This may also suggest a relationship between changes of productivity of the ocean influenced by smaller scale climate changes and loggerhead nest frequencies.

A study of the Nova Scotia surface air temperature over the last century (1900 to 2015) shows that internal variability on inter-annual, decadal and multi-decadal time scales can be partly explained by ocean-atmospheric climate modes, external and anthropogenic forcings. The Atlantic Multidecadal Oscillation (AMO) and Arctic Oscillation (AO) are shown to be the dominant climate drivers in Nova Scotia. The El Niño Southern Oscillation (ENSO) is also shown to be a dominant climate driver but only during the summer. Multivariate models were generated over the full time period using only natural ocean-atmospheric modes of variability but could not explain the rapid increase in the recent rate of warming (post-1980). The inclusion of anthropogenic greenhouse gas forcing to the models improved their predictive power annually and seasonally. The modelling results show that 11% of the annual variability in Nova Scotia results from natural forcings along with anthropogenic greenhouse gas forcing while seasonally up to 28% of the temperature variability can be explained by natural plus greenhouse gas forcings. The annual and seasonal low explained variance suggests that Nova Scotia is poorly modulated by climate indices, specifically during the winter, the time when relationships between ocean-atmospheric modes and the regional climate should be the strongest. It leads to believe that Nova Scotia is located in a transition zone where large-scale ocean-atmospheric modes of variability are transitioning from being positively correlated in a region to being negatively correlated in another region. The results of this study help to better understand how large-scale ocean-atmospheric modes of variability, external and anthropogenic greenhouse gas forcings affect Nova Scotia’s surface air temperatures and also provide insight into future potential variability under a changing climate.

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