Forests provide important ecosystem services and play a dominant role in the global carbon and hydrologic cycles. These ecosystems are becoming more vulnerable to climate change-related threats such as extreme temperature and precipitation events, drought and wildfires. In addition, forest ecosystems have also undergone land use changes and a significant reduction in cover area, specifically in North America. There has been renewed realization to restore and rehabilitate forest ecosystems because they are a major carbon sink and play a key role in sequestering atmospheric carbon dioxide. In response, plantation forests are being widely established to sequester carbon, increase biodiversity, secure water resources and generate economic revenue when harvested. Forest managers employ different management practices such as thinning or retention harvesting to enhance growth, plant structural and species diversity within forest plantations, with the ultimate goal of emulating the characteristics and benefits of natural forests. However, the influence of these forest management practices on the growth, productivity and specifically water cycling in plantation forests is not well studied and reported in the literature. This experimental study investigated the effect of four different variable retention harvesting (VRH) treatments on evapotranspiration and water balance in an 83-year-old red pine (Pinus resinosa) plantation forest in the Great Lakes region in Canada. These VRH treatments included 55% aggregated crown retention (55A), 55% dispersed crown retention (55D), 33% aggregated crown retention (33A), 33% dispersed crown retention (33D) and unharvested control (CN) plot. Tree-level experimental work was conducted in the control plot and showed that most of the water transport (65%) occurred in the outermost sapwood, while only 26% and 9% of water was transported in the middle and innermost depths of sapwood, respectively. These results help to avoid overestimation of transpiration, which may cause large uncertainties in water budgets in pine forests. Study results further showed that the 55D treatment had the highest tree-level transpiration followed by 33D, 55A, 33A and CN plots. During periods of low precipitation, vapor pressure deficit (VPD) was the main driver or control on transpiration in VRH treatments. However, transpiration was more closely coupled with photosynthetically active radiation (PAR) in the control plot. Moreover, the 55D treatment resulted in on average 58% of total water loss from canopy as transpiration and 42% from the understory and ground surface as evapotranspiration. These findings suggest that dispersed or distributed retention of 55% basal area (55D) provides the optimal environmental conditions for forest growth with reduced competition of trees for water as shown by enhanced transpiration. This study will help researchers, forest managers and decision-makers to improve their understanding of thinning impacts on water and carbon exchanges in forest ecosystems and select and adopt viable forest management practices to enhance their carbon sequestration capabilities, water use efficiency and resilience to climate change. / Thesis / Doctor of Philosophy (PhD)

Demand for both food and water are projected to increase substantially in the next four decades. Water scarcity is also projected to increase in scale and complexity. Climate change is projected to increase temperatures, spatio-temporal variability in rainfall, frequency and severity of droughts and soil water stresses to crops. Due to the crucial role of water in crop growth and yield formation, prolonged or severe soil water deficits in crop producing areas can result in substantial yield penalties. The potential of food trade to help address food insecurity as a result of insufficient water availability for crop production has been rationalized in the virtual water concept. The aim of this thesis was to improve the evidence base for understanding and evaluating the relationships between future water availability for crop production and food trade (or virtual water flows), and the utility of the virtual water concept to inform policy and management decisions on water-food security. The UK and barley were used as a model country and crop, respectively. Three crop growth simulation models (AquaCrop, CropWat and WaSim) were evaluated for their abilities to estimate the water use of 10 barley genotypes. Subsequently, the effect of projected climate change on UK barley yields in the 2030s, 2040s and 2050s was simulated using the high, medium and low emission scenarios data from the UK Climate Projections 2009 (UKCP09). Projections of total UK feed barley supply and demand were performed to quantify potential virtual water flows and to analyse the implications for food security and policy. The results show that the predicted water use of barley differed between the models but not among the genotypes. Predicted seasonal water use of the barley genotypes ranged from 241.4 to 319.2 mm. Based on the root mean square error (RMSE) and the index of agreement (D-Stat) values, CropWat performed poorly while AquaCrop and WaSim performed excellently. Barley yields under projected climate change increased substantially over baseline yields in all UK regions. Projected mean barley yields for the UK ranged from 6.04 tons ha-1 (2030s) to 7.77 tons ha-1 (2050s). In spite of the projected increase in yields, the UK faces the risk of large deficits in feed barley and meat supply from the 2030s to the 2050s due to a combination of population growth, increased per capita meat demand and reductions in land area allocated to barley production. Finally, current water scarcity concepts were found to be incompatible with water availability and consumption in crop producing areas, a situation that diminishes the usefulness of the virtual water concept for policy. To address this deficiency, a framework for making water scarcity compatible with crop production was proposed. In conclusion, the poor performance of CropWat has implications for its wider use in quantifying global virtual water flows associated with crop trade. Even though UK barley yields are projected to increase under projected climate change, the projected deficits in feed barley and meat supply threatens to destabilize future UK food security. The UK can rely on import to offset the large deficits in feed barley and meat supply but can use the proposed framework to reduce the effect of its imports on water scarcity in the exporting countries. The proposed framework improves understanding and evaluation of the role and usefulness of the virtual water concept in water-food security policy and management decisions.

This is a thesis about water efficiency, a particular set of practices in the water industry of England and Wales designed to reduce end-use water demand in homes and businesses. Broadly, the thesis aims to understand how water efficiency activities organised and funded by water companies might more effectively support the development of sustainable patterns of domestic demand, in order to contribute to long-term sustainable water management. To achieve this aim, mixed qualitative methods are used to; a) evaluate the extent to which two non-conventional water efficiency activities engage with the collective elements of everyday consumption that existing research deems necessary to steer demand (Strengers, 2012, Macrorie et al., 2014, Shove, 2014, Geels et al., 2015); b) develop a conceptual understanding of demand management as a professional practice, to understand how Water Company activities are shaped, sustained and stifled; and c) develop an understanding of what future water efficiency activities might look like that take account of the findings from this research. Central to this research and analysis is the notion of 'collective', a term that denotes a conceptual perspective on demand that departs from a focus on individuals, towards the shared social, technological and natural relations that structure everyday activity (Browne et al., 2014). The analysis uses this notion of collectives to examine the impacts and limitations of Save Water Swindon, a large-scale 'whole-town' approach to water efficiency (Case Study 1); to explore how Care for the Kennet contributes to demand management by reconfiguring relations between water in the home and water in the river (Case Study 2); and to uncover the collective context of the professional practices of managing demand (Case Study 3). The findings illustrate that demand is shaped by routines that extend far beyond the spaces in which water is used, both intentionally and unintentionally, and therefore highlight a distributed web of people and practices that might be involved in demand management. The findings from these empirical enquiries are used to as the basis to work with the water industry to reimagine interventions that engage in the collective context of demand, and elicit conceptual understandings of the processes and actors involved in governing social change. Overall, the approach taken in this thesis demonstrates the vitality of practice-based enquiry that provides deep analytical detail to better understand the mundane yet complex processes that sustain everyday water use. Supplementing the analysis with ideas from a variety of social science disciplines and working alongside the water industry, facilitated by the CASE studentship, pushes the analysis beyond the confines of domestic practices typical of practice-based research. Subsequently this research offers contributions to policy, practice and theoretical developments as it explores the intersections between demand and professional practices and local environments, evaluates interventions, examines practices of demand management, and unravels the possibilities for future intervention. Consequently, though focused on water management in the UK, this research offers insights for other resource agendas and regional contexts, expanding discussions in these spaces to think creatively about avenues for future policy and management practice.

Um statistische Zusammenhänge zwischen Lufttemperatur und Wassertemperatur zu analysieren, wurden zunächst in einer Vorstudie alle kurzfristig verfügbaren Temperaturmessungen in Oberflächengewässern sowie im Boden-, Sicker- und Grundwasser gesammelt, fehlerbereinigt und in Datenbanken zusammengeführt. Die erzeugten 600.000 Datensätze können direkt mit Daten zu Lufttemperatur, Sonnenscheindauer oder globaler Strahlung aus naheliegenden Wetterstationen verknüpft und somit für künftige Auswertungen genutzt werden. Die Prüfung unterschiedlicher Wassertemperaturmodelle hat gezeigt, dass sich für eine sachsenweite Analyse zur Abschätzung der Auswirkung des Klimawandels auf Wassertemperaturen die einfacheren statistischen Methoden aufgrund ihrer Datenverfügbarkeit eher eignen als die fachlich genauer erscheinenden komplexen Modelle mit Berechnungen zu Energiehaushalt und Wärmeaustausch von Gewässern. In Heft 40/2011 der Schriftenreihe werden die Zusammenhänge der klimawandelbedingten Lufttemperaturänderungen auf die Wassertemperaturen analysiert und detailliert dargestellt.