Estimating dominant runoff modes across the conterminous United States

Effective natural resource planning depends on understanding the prevalence of runoff generating processes. Within a specific area of interest, this demands reproducible, straightforward information that can complement available local data and can orient and guide stakeholders with diverse training and backgrounds. To address this demand within the contiguous United States (CONUS), we characterized and mapped the predominance of two primary runoff generating processes: infiltration‐excess and saturation‐excess runoff (IE vs. SE, respectively). Specifically, we constructed a gap‐filled grid of surficial saturated hydraulic conductivity using the Soil Survey Geographic and State Soil Geographic soils databases. We then compared surficial saturated hydraulic conductivity values with 1‐hr rainfall‐frequency estimates across a range of return intervals derived from CONUS‐scale random forest models. This assessment of the prevalence of IE versus SE runoff also incorporated a simple uncertainty analysis, as well as a case study of how the approach could be used to evaluate future alterations in runoff processes resulting from climate change. We found a low likelihood of IE runoff on undisturbed soils over much of CONUS for 1‐hr storms with return intervals \u3c5 years. Conversely, IE runoff is most likely in the Central United States (i.e., Texas, Louisiana, Kansas, Missouri, Iowa, Nebraska, and Western South Dakota), and the relative predominance of runoff types is highly sensitive to the accuracy of the estimated soil properties. Leveraging publicly available data sets and reproducible workflows, our approach offers greater understanding of predominant runoff generating processes over a continental extent and expands the technical resources available to environmental planners, regulators, and modellers

Flood Risk Assessment, Management and Perceptions in a Changing World

Floods are a global challenge that is increasing due to changes in climate and human populations. Using an interdisciplinary approach, this work contributes novel methodologies and knowledge to three key challenges associated with floods. The first chapter builds upon the atmospheric and statistical sciences to provide a general methodology for climate informed approaches to projecting long-term flood events based on large-scale ocean-atmospheric processes. The second chapter builds upon the engineering, decision analysis, and economics disciplines to integrate climate-informed projections with decision-scaling, a decision-making under uncertainty framework, to further flood risk management. The third chapter builds upon the social sciences to provide new knowledge on flood risk perception and mitigation in West Africa. The outcomes of this work contribute important advancements to addressing the clear and urgent need for solutions to floods around the world

STREAMFLOW TRENDS AND DROUGHT IN THE SOUTH ATLANTIC, U.S.: IMPLICATIONS FOR WATER MANAGEMENT AND WATER TRANSFERS

The South Atlantic has recently experienced region-wide droughts. There is concern that water scarcity may become more common or prevalent due to a warming climate. Problems associated with water scarcity are compounded by under-developed water allocation policy in the historically water abundant South Atlantic. This dissertation examined the potential causes of water scarcity related to changes in average streamflow from 1934-2005, 1934-1969 (Mid-20th Century) and 1970-2005 (Late-20th Century). Second, the contribution of climate versus anthropogenic drivers of change in mean annual streamflow in the Late 20th Century was evaluated using Budyko curves. Third, hydrologic drought was characterized in the South Atlantic and changes in drought characteristics were assessed over multiple time periods. Fourth, water interconnections, which form an important component of water infrastructure and water management, were assessed for the potential to transfer water from a drought free to a drought stricken area. Results showed that streamflow abruptly shifted from a drier regime in the Mid-20th Century to a wetter regime in the Late-20th Century with trends of significantly decreasing streamflow since 1970. Climate contributed to increased streamflow during the Late-20th Century throughout the South Atlantic; whereas human factors varied between basins and either amplified or decreased the climate change effect on streamflow. Human impacts were equivalent to or exceeded climate impacts in some basins. Seventy-one percent of drought events were shorter than 6 months with a recurrence interval of 6 years. Less than 7% of droughts were longer than one year, yet these longer duration droughts resulted in region-wide water scarcity. There were few significant temporal trends in drought characteristics over the studied time periods. The short interconnection distances (median=11.6 km) rarely extended beyond the spatial extent of multi-year droughts; interconnected water systems were simultaneously in drought 98±3% of the time from 2000-2008. Water managers face many challenges with a steadily growing demand and fluctuating long-term and short-term water supply needs that can be partially met through interconnections. Decision-making will benefit from monitoring changes in climate, human activities, and streamflow, as well as continually assessing the ability of current water infrastructure to perform under normal and adverse conditions.Doctor of Philosoph

The Hydrology of a Sandur-Wetland in a Volcanic Environment, Southeast Iceland

Iceland is a geothermally active island with sharp contrasts in climate and geography. A 2.5 km stretch of a proglacial river neighboring an inhabited wetland was monitored between September 2015 to September 2016. Water wells along transects coupled with pressure transducers monitored the water table response across this sandur-wetland landscape. Additional geomorphic and climatic data were also collected at this site in order to better understand the sandurs response to both seasonal and episodic weather events. UAV derived DEMs coupled with hydrological data, allowed for the mapping of flooding extents during the study period. Through a combination of climatological, hydrological and remote sensing means, this study attempts to provide spatial and temporal information of flooding levels in response to rainfall and episodic floods and seeks to better understand how variable/extreme events can generate significant hydrological and geomorphic changes within this dynamic sandur-wetland landscape

Extreme Floods and Droughts under Future Climate Scenarios

Hydroclimatic extremes, such as floods and droughts, affect aspects of our lives and the environment including energy, hydropower, agriculture, transportation, urban life, and human health and safety. Climate studies indicate that the risk of increased flooding and/or more severe droughts will be higher in the future than today, causing increased fatalities, environmental degradation, and economic losses. Using a suite of innovative approaches this book quantifies the changes in projected hydroclimatic extremes and illustrates their impacts in several locations in North America, Asia, and Europe

Hydrological Extremes in a Warming Climate: Nonstationarity, Uncertainties and Impacts

This Special Issue comprises 11 papers that outline the advances in research on various aspects of climate change impacts on hydrologic extremes, including both drivers (temperature, precipitation, and snow) and effects (peak flow, low flow, and water temperature). These studies cover a broad range of topics on hydrological extremes, including hydro-climatic controls, trends, homogeneity, nonstationarity, compound events and associated uncertainties, for both historical and future climates

ESTIMATING THE EFFECTIVE HYDRAULIC PROPERTIES OF THE SUBSURFACE AND THEIR SPATIOTEMPORAL RESPONSE TO CLIMATE USING A MODIFIED STREAMFLOW RECESSION ANALYSIS

Between periods of precipitation or snowmelt, the volume and timing of streamflow is largely determined by the properties of the subsurface and the time-varying distribution of groundwater storage. While streamflow during these periods (i.e., baseflow) is commonly treated according to a unique storage-discharge relationship, recent innovations in streamflow recession analysis have allowed novel findings regarding the variability of both the stability of baseflow and its nonlinearity (i.e., the concavity of the hydrograph), as well as the regional clustering of these characteristics. Here, I assess traditional and novel models of streamflow recession behavior using historical streamflow data from over 1,000 watersheds in the continental United States (US). Observed streamflow behavior from only nine watersheds often conforms to traditional models, and streamflow behavior from the vast majority (>99%) of watersheds typically conforms to a parsimonious parallel aquifer model which accounts for subsurface heterogeneity. I then apply this conceptual model alongside remotely-sensed estimates of watershed-scale groundwater storage and climate reanalysis estimates of watershed-scale soil moisture, rates of evapotranspiration, and cumulative precipitation to investigate seasonal patterns in both the stability and nonlinearity of streamflow that vary systematically across large regions. I find that coincident watershed storage is the best predictor of baseflow stability in many regions (particularly the Appalachian Mountains) while evapotranspiration from two to three months previous is the best predictor of baseflow stability in other regions (particularly the Pacific Northwest), and discuss the novel finding that streamflow nonlinearity has increased significantly in most watersheds across the US since 1980. Then, I estimate the effective hydraulic properties of all gaged watersheds in the continental US that are largely dam-free by adapting traditional methods of streamflow recession analysis to account for subsurface heterogeneity. Using these results, I develop models of effective hydraulic properties based on estimates of watershed topography, soils, bedrock, and climate, and apply these models to predict the effective hydraulic properties of all watersheds in the continental US. Key practical results of this analysis include: 1) the finding that streamflow is more stable during periods of extended drought than generally predicted; 2) the identification of regional patterns in the response of streamflow to climate change; and 3) a novel dataset representing the effective hydraulic properties of the subsurface for the entire continental US for use in regional-scale hydrological models.Doctor of Philosoph

Nao control on multi-annual periodicities in water resources and their utility for managing water resource extremes.

Water scarcity and the hazard of drought impacts millions of people worldwide, highlighting the need for robust water resource management. Forecasting of water resources (i.e., groundwater and streamflow) aids in the planning and preparedness for water resource extremes which, in turn, can help mitigate their societal and economic impacts. With the effects of climate change expected to exacerbate certain water resource extremes, there is increased pressure to develop improved ways to estimate future water resource behaviour. Hydrometeorological conditions in Europe are modulated by the North Atlantic Oscillation with important multiannual periodicities. Existing studies have shown that the NAO can drive multiannual periodicity behaviour in water resources and influence the timing of water resource extremes such as drought. As such, it has been discussed in hydroclimate literature that these multiannual relationships may have some utility in water resource forecasting applications. However, a systematic assessment of the relationship between the NAO and wide-scale water resources, at multiannual periodicities, has yet to be undertaken for large water resource datasets. Therefore, there is limited information to develop significant relationships between catchment properties and water resource response to multiannual NAO periodicity (e.g., magnitude, or lags), which may be of value in forecasting applications. The aim of this PhD thesis is to assess the feasibility of a relationship between the NAO and water resource variables, at multiannual periodicities, for indicating water resource behaviour (including extremes), at seasonal to multiannual timescales. This has been achieved using large hydrological datasets in the UK and the wavelet transform to characterise periodicities in these records and the NAOI. This research demonstrates that a significant and wide-spread ~7-year periodicity is exhibited by most UK water resources and has a significant relationship with the NAOI. Research presented here show that the degree of influence of this ~7-year periodicity is considerable, affecting groundwater median regional groundwater level anomalies by up to 0.71sd, and median regional streamflow anomalies by up to 0.55sd. These anomalies are also comparable to the projected effects of climate change on UK water resources. Findings demonstrate that there are notable non-stationarities of this multiannual NAO periodicity and its relation to UK water resource variables, with the ~7-year periodicity detected in water resources only being dominant since the 1970s. This has important implications for the applicability of existing water resource forecasting systems that have utilized data from this period (of a relatively stationarity frequency structure). Findings also demonstrate a second non-stationarity between the NAO and European rainfall, producing considerable uncertainties in the detection of lags between multiannual NAO periodicities and water resource response. At present, there is limited atmospheric research to explain these modes of non-stationarity in the NAO and their influence on water resources, which poses a substantial challenge to the application of these multiannual periodicities in water resource forecasting systems. Future cross-discipline work between atmospheric and hydrological sciences may be needed to account for these non-stationaries, and to better understand how the relationship between multiannual NAO periodicities and water resource response may be used in the forecasting of water resource behaviours.Natural Environmental Research (NERC)PhD in Water including Desig

Quantification of Compound and Cascading Hydroclimatic Extreme Events

Compound and cascading hydroclimatic extreme events have garnered much attention in recent studies. The combined effects of interconnected extremes can cause widespread damage, with a higher potential impact than individual extremes. Both anthropogenic warming and natural climate variability affect these extremes, which is why detecting past extreme events, understanding the underlying mechanisms, and assessing their future impacts can aid in mitigation efforts to reduce their overall impact. However, thus far, identifying such events is oversimplified and the propagation of their impact as cascades from the physical to human systems remains partly explored. The overreaching goal of this thesis is to develop robust methodologies to quantify the compound and cascading extreme events, such as drought and heatwaves, extreme precipitation and atmospheric rivers, extreme heat and humidity, and flash droughts in the past and future climate. A suite of advanced statistical methods, system dynamics, and causality approaches are implemented to achieve the research goal. This thesis consists of ten chapters, and the objective of each chapter are summarized as follows. (1) Chapter 1 provides a brief introduction and examples of various compound and cascading hydroclimatic extremes. (2) Chapter 2 provides a perspective of drought indices and highlights the challenges in the context of climate change. (3) The objective of chapter 3- chapter 5 is to quantify the compound drought and heatwave characteristics (frequency, duration, and severity) and investigate their association with natural climate variability, anthropogenic warming, land-climate feedback, and background aridity across the globe. (4) Chapter 6 is dedicated to quantifying the future changes in the potential impact of heat-stress (combination of extreme heat and humidity) on the human population. (5) The cascading influence of meteorological forcing on the moisture advection processes associated with extreme precipitation related to atmospheric rivers is discussed in chapter 7. (6) The objective of chapter 8 is to investigate and quantify the compound and cascading influence of different spatial drivers, such as precipitation, temperature, surface-energy portioning, soil moisture-temperature coupling strength, and vapor pressure deficit on the evolution and intensification of global flash droughts. (7) Chapter 9 proposes a methodology to quantify the compound and cascading effects in a dry-hot event network using a system dynamics approach. Finally, the conclusion and recommendations are provided in chapter 10