Paleotempestology, the study of past tropical cyclones (TCs) using geological proxy techniques, is a growing discipline that utilizes data from a broad range of sources. Most paleotempestological studies have been conducted using “established proxies”, such as grain-size analysis, loss-on-ignition, and micropaleontological indicators. More recently researchers have been applying more advanced geochemical analyses, such as X-ray fluorescence (XRF) core scanning and stable isotopic geochemistry to generate new paleotempestological records. This is presented as a four article-type thesis that investigates how changing climate conditions have impacted the frequency and paths of tropical cyclones in the western North Atlantic basin on different spatial and temporal scales. The first article (Chapter 2; Oliva et al., 2017, Prog Phys Geog) provides an in-depth and up-to-date literature review of the current state of paleotempestological studies in the western North Atlantic basin. The assumptions, strengths and limitations of paleotempestological studies are discussed. Moreover, this article discusses innovative venues for paleotempestological research that will lead to a better understanding of TC dynamics under future climate change scenarios. The second article (Chapter 3; Oliva et al., submitted, The Holocene) presents the development of the first database summarizing the most up-to-date paleotempestological proxy data available for TC reconstructions for the western North Atlantic basin. Subsets of this new database are then used to reconstruct TC variability in the western North Atlantic basin. Using our new developed subsets, we investigate a key hypothesis, the Bermuda High Hypothesis that has been proposed to have influenced TC paths over centennial to millennial timescales. Results show an oscillation in the distribution of TC landfalls along the North American coast, suggesting a centennial oscillation in the mean summer position of the high pressure system. We suggest that a more serious, millennial scale shift in the Bermuda High to a northeastern (NE position) may have occurred at ~3000 and ~1000 cal yr BP. The third article (Chapter 4; Oliva et al., under review, Marine Geology) presents a local multi-proxy reconstruction of TC activity during the past 800 years from Robinson Lake, Chezzetcook Inlet in Nova Scotia, Canada. Here, we are testing the more recent use of the XRF scanning approach to paleotempestology at a local scale. Two sediment cores were extracted from Robinson Lake that were dated by 210Pb and 14C, analyzed for organic matter content, benthic foraminifera and thecamoebians, sediment grain size, and a range of elements and elemental ratios determined by XRF core scanning. Results show two periods of low TC activity based on multiple proxies including XRF technology: one from ~1150 to 1475 CE (800 – 475 cal yr BP) and the other from 1670 CE (280 cal yr BP) to the present, with the intervening period from ~1475 to 1670 CE (475 – 280 cal yr BP) as a time of more frequent and possibly higher magnitude TC activity. The fourth article (Chapter 5. Oliva et al., in preparation, Canadian Journal of Earth Sciences) explores the potential use of stable oxygen isotopes in tree ring α-cellulose to reconstruct past local TC activity surrounding areas of known TC strikes. Cores of 12 Picea mariana trees were extracted adjacent to Robinson Lake, Chezzetcook Inlet, Nova Scotia in order to test more contemporary and historically documented records of TC activity in this region as per Chapter 4. TCs precipitate 18O-depleted rain, leaving a unique signature in the source water that trees use to form cellulose. Using an autoregressive integrated moving average (ARIMA AR-1) model to detrend the data, local and regional time series were reconstructed. Local reconstructions led to most (> 95%) hurricanes and all major hurricane (± 1 year) being recorded in the isotope record, whereas the regional reconstruction shows no major hurricane, only a few hurricanes (< 40%) and one signal with a higher error (> 1 year). This thesis contributes to advancing our knowledge in paleotempestology of the western North Atlantic basin by: 1) bringing an up-to-date current status on paleotempestology, 2) the development and ongoing use of a new paleotempestology database for the western North Atlantic basin publicly available, 3) a local scale study using new XRF core elemental technology and 4) the exploratory use of tree-ring α-cellulose oxygen isotopic analysis based on contemporary and historical documents at local sites.

The single greatest uncertainty in seasonal water supply forecasts is the amount of precipitation falling after the forecast issue date. There has been a long history of attempting to incorporate seasonal climate forecasts into operational water supply forecasts. The skill of these precipitation forecasts remains low especially compared to highly confident snow-based streamflow forecasts. Early in the season (e.g., September-December), however, large-scale climate indices are the best available predictors of future water supplies. This dissertation suggests practical methods for issuing climate-based operational streamflow forecasts.This study also documents the existence of strong decadal trends in water supply forecast skill. Across the Western US, 1 April forecast skill peaked in the 1960-1970s and has been on the decline more recently. The high skill period was a very calm period in the Western US, with a near absence of extreme (wet or dry) spring precipitation events. In contrast, the period after 1980 has had the most variable, persistent, and skewed spring and summer streamflows in the modern record. Spring precipitation is also now more variable than it has been since at least the 1930s. This rise in spring precipitation variability in the Colorado/Rio Grande Basins and the Pacific Northwest is the likely cause behind the recent decline in water supply forecast skill.

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Research indicates a warming global climate leads to change in the spatial and temporal characteristics of precipitation. Although precipitation is inherently variable through time and space, for some water-sensitive stakeholders, the evenness with which precipitation is distributed through a time interval rivals the importance of total precipitation amount and frequency within that period. This study uses a relatively new approach of analyzing inequity in the temporal distribution of precipitation to examine the recent historical record of precipitation across the United States. The Gini coefficient (GC), which has been commonly used in the field of economics to measure wealth distribution, was used here to assess inequity in the temporal distribution of daily precipitation through seasonal and annual timeframes. Additionally, the Lorenz asymmetry coefficient (LAC) was used to assess the magnitude of daily precipitation events (light, heavy) associated with inequity in the temporal distribution of precipitation. The concept of using these two metrics together to quantify changes in the character with which precipitation occurs across a time interval has yet to be documented for areas within the United States. Therefore, this study expands upon previous research of long-term hydroclimatic change and variability by illustrating the combined ability of these two relatively under-utilized metrics, the GC and the LAC, to enhance quantification of recent change in the characteristics of the temporal distribution of daily precipitation across the United States. The first element of the research presented here is demonstration of the utility of the GC and LAC metrics using data from the physically diverse mid-Atlantic sub-region of the United States. This research used station-level daily precipitation data to compute historic time series of intra-annual and intra-seasonal precipitation amount, precipitation frequency, GC, LAC, variance (V), and interquartile range (IQR). The results of this portion of the research show that when compared to other simpler measures of characterizing variability (i.e., V and IQR), the GC is relatively robust to both the number of days with precipitation and the total precipitation received in a temporal increment (i.e., season or year). The research expanded in scale to the continental United States, requiring data integration to a regional level to facilitate data analysis and physical understanding. The analysis used gridded seasonal means (1981 – 2010) of four precipitation characteristics: precipitation amount, precipitation frequency, GC, and LAC to delineate regions of homogenous precipitation characteristics. To accomplish this, a multi-step regionalization technique was employed. Specifically, the historic seasonal means were subjected to a Principal Components Analysis (PCA), and the resulting component scores were subjected to several cluster analysis techniques. The average linkage clustering technique produced the most logical clustering solution, indicating that 15 regions of homogenous precipitation exist within the contiguous United States. It is argued that the regions better serve hydroclimatic analyses than the nine climate regions designated by the United States National Centers for Environmental Information (NCEI). The third element of the research integrates the first two research elements in study of recent United States hydroclimate variability and change. For the 15 United States hydroclimate regions, regionally averaged water year time series (1949 – 2018) of precipitation amount, precipitation frequency, GC, and LAC were computed using in-situ precipitation data gathered from the NCEI's Global Historical Climatology Network (GHCN)-Daily database. The time series of all precipitation characteristics for each region were then subjected to the nonparametric Mann-Kendall trend test to assess the significance of each trend, and the Sen's slope estimator was used to quantify the magnitude of the trend. Time series that characterize two key atmospheric characteristics, total column water vapor and static stability, were also computed for each region. For most of the 15 study regions, water year total precipitation and precipitation frequency increased through the latter half of the 20th century. The largest magnitude of change in water year total precipitation and precipitation frequency occurred in the time series of regions located within the eastern and northern portions of the contiguous United States. Results also show that inequity in the temporal distribution of water year precipitation increased through the 70-year study period for most of the 15 study regions. Combined, these results indicate that days with light and heavy precipitation are becoming more prevalent at the expense of days with moderate precipitation. Furthermore, variability in the time series of some precipitation characteristics for several regions coincide with variability in the atmospheric variables that characterize total column water vapor and static stability, however the dominant driver of hydroclimatic change across the contiguous United States remains elusive. / Doctor of Philosophy / Research indicates a warming global climate leads to change in the spatial and temporal characteristics of precipitation. These changes could adversely affect some water-sensitive stakeholders who are concerned not only with the amount of precipitation received over time, but also with the manner in which the precipitation is distributed through time – all at once, or spread evenly. The Gini coefficient (GC), which has been commonly used in the field of economics to measure wealth distribution, was used here to assess inequity in the temporal distribution of daily precipitation through seasonal and annual timeframes. Additionally, the Lorenz asymmetry coefficient (LAC) was used to assess the magnitude of daily precipitation events (light, heavy) that were primarily responsible for inequity in the distribution of daily precipitation amounts through each time interval. The research presented here used gridded seasonal means (1981 – 2010) of four precipitation characteristics: precipitation amount, precipitation frequency, GC, and LAC to delineate regions of homogenous precipitation characteristics. Through this process, 15 hydroclimatic regions were delineated within the contiguous United States. Regionally averaged annual time series (1949 – 2018) of precipitation amount, precipitation frequency, GC, and LAC were computed for each region using station-level precipitation. The time series of each precipitation characteristic, and for each region were then examined for statistical trends through the 70-year study period. Regional time series which characterize two key atmospheric characteristics, total column water vapor and static stability, were also computed for each region. For most of the 15 study regions, water year total precipitation and precipitation frequency increased through the latter half of the 20th century. The largest magnitude of change in water year total precipitation and precipitation frequency occurred in the time series of regions located within the eastern and northern portions of the contiguous United States. Results also show that precipitation became less evenly distributed across the water year through the 70-year study period for most of the 15 study regions. Combined, these results indicate that days with light and heavy precipitation are becoming more prevalent at the expense of days with moderate precipitation. Furthermore, variability in the time series of some precipitation characteristics for several regions coincide with variability in the atmospheric variables that characterize total column water vapor and static stability, however the dominant driver of hydroclimatic change across the contiguous United States remains elusive.

Hydroclimatic variability in the western United States (the West) is characterized by a north-south dipole pattern of precipitation and streamflow variance, with centers of opposite association in the Pacific Northwest and the Desert Southwest. These dipole centers tend to react in opposite fashion to tropical Pacific Ocean conditions, and the resulting contrast in precipitation variability is an important component of Western climate. Teleconnection impacts are not as well understood in the transition zone separating the centers of opposite association, located primarily within the semi-arid Intermountain West. This leads to low hydroclimatic predictive capacity in the transition zone region, an area that is extremely important for water supply in the West. In this dissertation, I examine paleohydroclimatic variability in this region using dendrochronology, investigate recent variability through a synoptic climatology approach, and assess future conditions based on climate change projections.Overall, this dissertation's findings confirm that the transition zone region is highly vulnerable to extremes in hydroclimatic variability and underscore the need for improved predictive capacity in the region. In the Snake River headwaters, low- to mid-elevation Pseudotsuga menziesii trees are the strongest recorders of winter precipitation, a vital component of water supply, and the season of precipitation impacting growth is a major component of the overall variability between tree-ring sites in the region. The 415-year reconstruction of Snake River streamflow indicates that extended droughts, more severe than those recorded in the instrumental period, have occurred in the pre-instrumental past. Streamflow in the upper Snake River is strongly linked to Pacific Ocean conditions and sensitive to storm track position. The West's precipitation dipole has a surprisingly narrow transition zone that has shifted in its location over time in some areas but has remained remarkably stationary across Nevada and Utah. Projected climate changes - including warmer temperatures, changing seasonality, reduced snowpack, and changes in the storm track position - highlight the importance of understanding climate-water linkages for future water resource management.

This study proposes a stratified approach of drought severity assessment using multi-layer simulated soil moisture. SWAT (Soil and Water Assessment Tool) models are calibrated for 50 watersheds in the South-Atlantic Gulf region of the Southeastern US and a high-resolution daily soil moisture dataset is obtained at Hydrologic Unit Code (HUC-12) resolution for a period of January 1982 through December 2013. A near real-time hydrologic simulation framework by coupling the calibrated SWAT models with the National Centers for Environmental Prediction (NCEP) coupled forecast system model version 2 (CFSv2) weather data is developed to forecast various water balance components including soil moisture (SM), actual evapotranspiration (ET), potential evapotranspiration ET (PET), and runoff (SURQ) for near-real time drought severity assessment, and drought forecasting for a lead of 9-months. A combination of the surface and total rooting depth soil moisture percentiles proves to be an effective increment over conventional drought assessment approaches in capturing both, transient and long-term drought impacts. The proposed real-time drought monitoring approach shows high accuracy in capturing drought onset and propagation and shows a high degree of similarity with the U.S. Drought Monitor (USDM), the long-term (PDSI, PHDI, SPI-9 and SPI-12), and the short-term (Palmer Z index, SPI-1 and SPI-6) drought indices. / Master of Science / Drought, a recurring and worldwide phenomenon, with spatial and temporal characteristics varying significantly from across globe, lead to long-term and cumulative environmental changes. Often referred to as creeping phenomena, droughts are difficult to predict and constant monitoring is required to capture the signs of the onset of drought. Spatial variability in drought severity requires an understanding of the hydrology of the region and a knowledge of the relationship between drought inducing climatic extremes and other regional or local characteristics which help build, sustain and propagate droughts. In the absence of long-term observed hydrologic variables like soil moisture, evapotranspiration, simulated hydrologic variables serve an important purpose in understanding the impact of drought on various components of the water budget. However, several continental scale, physics-based models, and large scale remote sensing products find themselves restricted in explaining the watershed scale and sub-watershed scale variability in relation to drought. This study provides a high-resolution simulation of hydrological variables for 50 watersheds in the South-Atlantic Gulf region of the Southeastern US. The high resolution hydrologic simulations provide bedrock for retrospective drought simulations and understanding the response of various hydrologic variables of these watersheds to drought. It also aids in understanding the spatial variability in the relationship, and understanding the impact of seasonality and hydroclimatology on drought. The understanding of the interplay of various water budget components at watershed scale is used in developing a reliable seasonal drought forecasting framework based on the forecasted hydrologic variables from SWAT-CFSv2 coupled models for application in real time with a lead time of 9 months.

Tendo em vista o papel que as chuvas exercem sobre águas continentais e a consequente disponibilidade hídrica para abastecimento, geração de energia, produção de alimentos e a dinâmica climatológica regional, o estudo de periodicidades nas variações em séries temporais pluviométricas têm impactos relevantes para o planejamento dos recursos hídricos. A precipitação, enquanto elemento do sistema climático, está em função de fatores internos e forçantes extraterrestres. Dentre estas, a força da gravidade da lua tem papel significativo como motor das marés oceânicas e sua influência na distribuição da massa e calor em escala global. Com o objetivo de identificar longos períodos de variação hidroclimática, esse trabalho investigou ciclos em escala decenal na variabilidade de seis séries longas de precipitação na região hidrográfica do Paraná no Sudeste Brasileiro, e sua potencial relação com o ciclo nodal de 18,6 anos. Para alcançar esse objetivo, além das análises estatísticas clássicas de dados, foi utilizado o filtro HP com o intuito de separar componentes de cíclicas e de longo prazo. Foi utilizada a metodologia de análise espectral de dados, como Fourier e a transformada em wavelet, que determina o poder das componentes dentro de uma série temporal. As análises estatísticas e o filtro HP foram importantes na visualização e detecção de períodos persistentes de desvios em relação aos valores médios. A ferramenta de transformada em wavelet apontou para robusta presença de periodicidades decenais em todas as séries, sendo as mais significativas 9 anos e 19 anos para todas as séries, com significância superior a 95%. Os resultados sugerem uma aparente anticorrelação, ou seja, o mínimo do ciclo nodal coincide com um incremento nos totais pluviométricos na região. Assim, essas informações da influência podem aprimorar a previsibilidade de condições hidrológicas interdecenais médias e aquelas variáveis socioeconômicas que são sensíveis à precipitação. / Considering the role of rainfall on continental waters and resulting water availability for water supply, energy generation, food production and regional climatological dynamics, the study of periodicities in variations in rainfall time series has a relevant impact on resource planning Water resources. Precipitation, as an element of the climate system, is a function of internal factors and extraterrestrial forcing. Among these, the force of gravity of the moon plays a significant role as the motor of the ocean tides and its influence on the distribution of mass and energy on a global scale. In order to identify long periods of hydroclimatic variation, this work investigated decadal scale cycles in the variability of six long series of precipitation in the Paraná hydrographic region in southeastern Brazil, and its potential relation with the nodal cycle of 18.6 years. To achieve this goal, in addition to the classic statistical data analysis, the HP filter was used in order to separate components from cyclical/random and long term. We use the spectral data analysis methodology, such as Fourier and the wavelet transform, which determines the power of the components within a time series. Statistical analyzes and the HP filter were important in visualizing and detecting persistent periods of deviations from mean values. The wavelet transform analysis pointed to robust presence of decadal periodicities in all series, being the most significant 9 years and 19 years for all series, with significance higher than 95%. The results suggest an apparent anticorrelation, that is, the minimum of the nodal cycle coincides with an increase in the total rainfall in the region. Thus, this influence information can enhance the predictability of medium interdecadal hydrological conditions and those socioeconomic variables that are sensitive to precipitation.

Orientador: Thiago Sanna Freire Silva / Resumo: Os sistemas montanhosos são laboratórios naturais para análise de gradientes. Elevação, amplitude e diferenças topográficas em montanhas podem criar fortes diferenças microclimáticas a curtas distâncias, aninhadas dentro da mesma região biogeográfica e macroclimática, permitindo-nos compreender melhor as respostas da vegetação e os feedbacks sobre a disponibilidade de água. Neste estudo, avaliamos como a distribuição da vegetação está ligada à disponibilidade de água na Serra do Espinhaço. Para tanto, abordamos as seguintes questões: 1) Quais são os regimes hidroclimáticos encontrados na Serra do Espinhaço e seus correspondentes tipos de vegetação? 2) Onde a produtividade da vegetação é mais e / ou menos acoplada aos regimes hidroclimáticos? 3) A topografia é capaz de impactar a produtividade da vegetação e suas relações de acoplamento com regimes hidroclimáticos? Além disso, considerando estas relações ambientais e de vegetação, 4) Como a resiliência climática dos tipos de vegetação nesta região varia? Conclui-se que na faixa do Espinhaço, a maior parte da dinâmica de produtividade da vegetação espaço-temporal é impulsionada por condições hidroclimáticas e / ou topo-edáficas. Nossos resultados mostram que a vegetação da Caatinga teve uma resposta plástica e relativamente rápida ao Déficit Hídrico Climático (CWD) e foi o tipo de vegetação com maior restrição hídrica. Cerrado e Campos Rupestres tiveram respostas semelhantes às flutuações no déficit hídrico, mostrando um gradie... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Montane systems are natural laboratories for gradient analysis. Elevation, amplitude and topographical differences over mountains can create strong microclimatic differences over short distances, nested within the same biogeographic and macro-climatic region, thus allowing us to better understand vegetation responses and feedbacks to water availability. In this study, we assessed how vegetation distribution is linked to water availability in the Espinhaço Mountain Range. For that, we addressed the following questions: 1) Which are the hydroclimatic regimes found in the Espinhaço Range and their corresponding vegetation types? 2) Where does vegetation productivity is more and/or less coupled to hydroclimatic regimes? 3) Is topography able to impact vegetation productivity and its coupling relations to hydroclimatic regimes? Also, considering these environmental and vegetation relationships, 4) How does the climatic resilience of the vegetation types in this region vary? We conclude that in the Espinhaço Range, most of the spatio-temporal vegetation productivity dynamics are driven by hydroclimatic and/or topo-edaphic conditions. Our results show that “Caatinga” vegetation had a plastic and relatively fast response to Climatic Water Deficit (CWD) and was the most water-constrained vegetation type. “Cerrado” and “Campos Rupestres” had similar responses to fluctuations in water deficit, showing a gradient of slower to faster responses from “Humid” to “Very dry” hydroclimatic regi... (Complete abstract click electronic access below) / Mestre

<p>Seasonally dry ecosystems cover large areas over the world, have high potential for carbon sequestration, and harbor high levels of biodiversity. They are characterized by high rainfall variability at timescales ranging from the daily to the seasonal to the interannual, and water availability and timing play key roles in primary productivity, biogeochemical cycles, phenology of growth and reproduction, and agricultural production. In addition, a growing demand for food and other natural resources in these regions renders seasonally dry ecosystems increasingly vulnerable to human interventions. Compounded with changes in rainfall regimes due to climate change, there is a need to better understand the role of climate variabilities in these regions to pave the way for better management of existing infrastructure and investment into future adaptations. </p><p>In this dissertation, the ecohydrological responses of seasonally dry ecosystem to climate variabilities are investigated under a comprehensive framework. This is achieved by first developing diagnostic tools to quantify the degree of rainfall seasonality across different types of seasonal climates, including tropical dry, Mediterranean, and monsoon climates. This global measure of seasonality borrows from information theory and captures the essential contributions from both the magnitude and concentration of the rainy season. By decomposing the rainfall signal from seasonality hotspots, increase in the interannual variability of rainfall seasonality is found, accompanied by concurrent changes in the magnitude, timing, and durations of seasonal rainfall, suggesting that increase in the uncertainty of seasonal rainfall may well extend into the next century. Next, changes in the hydrological partitioning, and the temporal responses of vegetation resulting from these climate variabilities, are analyzed using a set of stochastic models that accounts for the unpredictability rainfall as well as its seasonal trajectories. Soil water storage is found to play a pivotal role in regulating seasonal soil water hysteresis, and the balance between seasonal soil water availability and growth duration is found to induce maximum plant growth for a given amount of annual rainfall. Finally, these methods are applied in the context of biodiversity and the interplay of irrigation and soil salinity, which are prevailing management issues in seasonally dry ecosystems.</p> / Dissertation

A large portion of the freshwater in western Canada originates as snowpack from the northern Rocky Mountains. The temperature and precipitation in these areas controls the amount of snow accumulated and stored throughout the winter, and the amount and timing of melt that occurs during the spring freshet. Therefore, a better understanding of past and future changes to the extent of snowpack and timing of melt can modify the timing of peak river flow on a continental scale. Trends in temperature, precipitation, snow accumulation, and snowmelt are examined using the Mann-Kendall non-parametric test on a high resolution gridded climate dataset over western Canada for the period 1950-2010. In addition, projected changes in temperature, precipitation, snow water equivalent, and snowmelt are examined through comparison of the current (1971-2000) and future (2041-2070) time periods incorporating several regional climate models. The temporal and spatial analyses of these key hydroclimatic variables indicate that changes vary greatly over space and time. Results reveal that while both maximum and minimum temperature have increased in the past 60 years, minimum temperature has increased more than maximum temperature and is likely to continue doing so in the future. This trend is particularly evident during the colder months of the year, and at higher elevations, contributing to earlier spring melt. Between 1950 and 2010, precipitation has decreased throughout the colder months of the year and increased in the warmer months, particularly in the northern half of the study area. Future projections show increased precipitation, specifically in the north. Throughout the historical period snow accumulation has experienced decreases across the study area and through all months of the year, except for increases at high elevations. In the coldest months of the year snow accumulation is projected to increase in high elevation and northern areas while decreasing across the rest of study area in the future. Snowmelt results indicate slight increases in mid-winter melt events and an earlier onset of the spring freshet; this change is expected to continue into the future period. This study provides a summary of detected trends and potential future changes in key hydroclimatic variables across western Canada with regard to the effects these changes can have on the spring freshet and streamflow, and thus water resources, throughout the study area. / Graduate / 0368