Doctoral Theses / Doktorsavhandlingar Institutionen för geovetenskaper

Permanent URI for this collectionhttps://gupea-staging.ub.gu.se/handle/2077/17671

Browse

Now showing 1 - 20 of 58

Spatial Contextualization of Heat Mitigation and Recreational Aspects of Greenery in Various Urban Environments
(2025-05-21) Bäcklin, Oskar
Urban greenery has significant potential to provide heat mitigating and recreational functions for urban residents. However, the ability of greenery to deliver these benefits is highly dependent on its spatial context. The aim of this thesis is to examine how greenery—and its heat-mitigating and recreational functions and benefits—is spatially distributed in residential and everyday environments. It also seeks to develop methods to assess and compare the functions that different types of greenery can offer, depending on spatial context and planning needs. The first two papers show that access to greenery in residential environments varies across housing typologies, resulting in unequal access to its recreational benefits. They also highlight that greenery, particularly trees, plays a crucial role in reducing heat stress in preschool yards—many of which currently lack sufficient shade—as well as in providing recreational benefits in residential areas. The third paper demonstrates that the cooling potential of trees is strongly influenced by surrounding ground conditions. Trees growing in areas with a higher proportion of permeable surfaces can grow larger, transpire more, and provide more effective shade, thereby enhancing their cooling effect. The final two papers contribute methods for assessing the multifunctionality of greenery and for better integrating spatial context into urban planning and analysis. The results show that the unctional and multifunctional potential of different green elements varies, with generally low overall multifunctionality. Thus, while multifunctionality is a desirable goal, specific functions may need to be prioritised in certain contexts to meet local needs. The findings also emphasise the importance of proper parametrisation of urban climate models to accurately reflect local conditions within the model domain. In summary, this thesis emphasises the importance of considering spatial context in the study and planning of urban greenery. It contributes new knowledge on the variation in functions and benefits of greenery in everyday environments and offers practical tools to support planners and decision makers in more effectively integrating greenery into urban development, adapted to spatial context and local needs
Evaluation and projection of the changes in near-surface wind speed: implication for wind energy potential
(2024-08-10) Shen, Cheng
Understanding variations in near-surface wind speed (NSWS) is scientifically challenging and crucial for the optimal utilization of wind energy and air quality. Changes in NSWS are linked to variations in atmospheric and surface conditions, such as large-scale atmospheric circulations, land use/cover changes, and anthropogenic aerosols. However, the influences of other factors, such as volcanic eruptions, and anthropogenic greenhouse gases (GHGs), remain largely unexplored. This thesis aims to investigate the impact of volcanic eruptions on the changes in NSWS in the past, and to reliably project the future changes concerning onshore and offshore wind energy potential under global warming, induced by GHGs. Specifically, the thesis addresses the following scientific questions: (1) what is the performance of global climate models in reproducing the past NSWS over land, and how to get reliable future projections? (2) how past volcanic eruptions affect global NSWS? (3) To what extent is wind energy generation affected by the changes in NSWS? Results indicate that most global climate models significantly underestimate the observed NSWS trends over land. The projection uncertainty can be expected to be reduced by selecting the model with the most historical fidelity, which can reasonably reproduce past trends. Additionally, this thesis provides evidence of a robust two-year reduction in global NSWS following tropical volcanic eruptions, exemplified by up to ~9.2% decrease in global wind power density after the 1815 Tambora eruption. This reduction is linked to the weakening of subtropical descending air corresponding with a decrease in downward momentum flux, triggered by volcanic aerosol forcing. Finally, this thesis projects future global offshore NSWS and wind potential density under different scenarios, with an example focus on China. After performing a correction method, global offshore wind power density is expected to increase in future, with an anticipated rise of 4-18% under four emission scenarios by the end of the 21st century. The findings in this thesis improve our understanding of the changes in NSWS and the implication to wind energy production. Specifically, this thesis highlights the potential risk of wind energy deficits associated with atmospheric aerosol injections from large volcanic eruptions, also highlights the growing importance of offshore wind in our energy mix and underscores the need for improved modeling to guide investments and policies.
High-resolution dynamics of the deep Arctic Ocean: From thin meltwater layers to large-scale transport
(2024-05-10) Karam, Salar
The Arctic has arguably undergone the most rapid environmental changes in the world in recent decades due to climate change. Climate change in the Arctic has a large range of climatic and societal impacts, such as sea level rise and large-scale changes in the oceanic circulation, which affect the global climate as a whole. The deeper water masses of the Arctic Ocean have similarly undergone large structural changes in recent decades, however the lack of observational data makes it difficult to understand the role of the deep ocean for the global climate. Through the use of global climate model output and observational data collected in field campaigns as part of this project, the work in this dissertation sets out to improve the understanding of the deep Arctic Ocean, a rapidly evolving and simultaneously poorly understood part of the climate system. Through analyses of global climate models, a number of biases were found in the central Arctic Ocean, which were related to poor sea ice-ocean coupling and inaccurate properties introduced further upstream in the adjacent Nordic Seas. Using observational data, the significance of small-scale sea ice-ocean processes was highlighted. Additionally, new circulation pathways were discovered, and it was found that eddies likely have an important role for setting deep oceanic properties over large spatial scales. Finally, it was found that the deep waters of the Greenland Sea are now a heat source for the central Arctic Ocean, due to a strong warming trend that occurred as a result of the cessation of deep convection in the 1980's. The biases found in the models, and the importance these processes were found to have in observations, suggest that these processes need to be better considered in future iterations of global climate models. This dissertation therefore provides another step towards understanding the Arctic.
Trophic interactions in the tundra: Impacts of large mammal herbivory on carbon processes and fungal communities
(2023-12-11) Brachmann, Cole
Plant productivity is generally increasing in the Arctic as a consequence of accelerated climate change. The change in plant communities may coincide with a loss of carbon from Arctic soils due to increased decomposition and respiration. Herbivores can mediate these changes through preferential foraging on highly productive plant species, trampling, and waste deposition. Soil fungi are also a major component in these interactions and are controlled by plant community and soil conditions. Soil fungi have large impacts on the cycling of carbon in soil and its subsequent release to the atmosphere. Understanding of the effects of large mammalian herbivores on carbon processes, such as respiration and decomposition, and fungal communities is important for understanding the context of future changes in carbon storage in tundra soils. I investigated the effect of herbivory on trace gas fluxes, decomposition and stabilization of organic matter, and soil fungal communities through the use of herbivore exclusion fences in tundra communities. Herbivory reduced ecosystem respiration in a meadow community, reduced stabilization under a deciduous shrub in a heath community, reduced arbuscular mycorrhizal fungi across the Arctic, and reduced ectomycorrhizal fungi locally in Swedish tundra. The presence of herbivores on the landscape can have complex effects on carbon in tundra habitats by reducing respiration rates and limiting fast cycling arbuscular mycorrhizal fungi, while simultaneously reducing the stability of organic matter as it decomposes and locally limiting slower cycling ectomycorrhizal fungi. The relative contribution of each of these processes to carbon cycling will determine the net effect of herbivores on tundra soils. Herbivory impacts are context dependent and the net effect on soil carbon is likely related to the proportion of different tundra community types on the landscape.
Climate-associated human health effects
(2023-08-11) Chen, Tzu Tung
The intensifying impacts of climate change on human health represent a significant and pressing global health threat of the current century. This encompasses both short and long-term effects on human health, as well as ecosystem changes linked to rapid shifts in climate, and the subsequent spread of vector-borne diseases. The complex interplay between climatic factors, socioeconomic variables, and health outcomes poses significant challenges for contemporary studies. Moreover, investigations into climate-associated health burdens in historical times are constrained by the paucity of extensive datasets. This dissertation explores the spatial and temporal patterns of health impacts in response to climatic variability during the late pre-industrial era (here, 1749－1859) in the Nordic region including Denmark, Sweden, and Finland. The primary dataset used in this dissertation comprises malaria data (cases and deaths) and all-cause deaths obtained from parish-level vital statistics for the period of 1749 to 1859. To investigate the association between climate and malaria, the distributed lag non-linear model (DLNM) was applied to capture nonlinearity and lag effects of time-varying environmental exposures on malaria risk in Denmark, Sweden, and Finland. Additionally, a spatiotemporal analysis was conducted to explore the climate－mortality relationship in Sweden. This analysis involved comparing excess mortality with gridded climate datasets. Results from this dissertation present historical evidence of the significant impacts of climate-related changes on both malaria and mortality in temperate regions like the Nordic countries. The analysis demonstrates the influence of temperature, precipitation, and sea-level change on malaria risk, as well as the seasonal association between climate and mortality levels. Moreover, this work identifies diverse lag effects of climate impacts on mortality across different geographical areas in Sweden. These findings underscore the relevance of climate factors in comprehending infectious diseases and mortality dynamics during the pre-industrial era in the Nordic region. By enhancing our understanding of the historical association between climate and health outcomes, this dissertation contributes valuable insights to inform future strategies for mitigating the current and future health risks associated with climate change.
Towards an improved understanding of precipitation variations over the Tibetan Plateau
(2023-05-09) Lai, Hui-Wen
The Tibetan Plateau (TP) and surrounding regions are known as the ``Third Pole'' because of their polar-like environment and large reservoirs of fresh water. Due to the latter aspect, the TP is also considered the ``Water Tower of Asia'', providing essential water resources to the surrounding regions. The most important supply to this water tower is atmospheric precipitation, which is affected by both local processes, such as convection and orographic lifting, and remote mechanisms including atmospheric circulation patterns, such as dynamics of monsoon systems and the westerly jets. However, how precipitation over the TP has changed spatially and temporally and the key mechanisms behind these changes remain to be fully understood. This dissertation addresses the following research questions related to TP precipitation: 1) How does the seasonality of TP precipitation vary spatially, and what roles do large-scale atmospheric circulation patterns over and around the TP play in determining precipitation seasonality? 2) Can fine-resolution regional atmospheric models simulate precipitation over the TP more realistically than state-of-the-art global reanalysis datasets? The dissertation aims to advance our understanding of precipitation and related large-scale to mesoscale processes over the TP using ground-based and remote sensing observations, reanalyses, and high-resolution atmospheric modeling. Specifically, the dissertation focuses on the seasonality and interannual variability of regional precipitation, as well as long-term changes in atmospheric large-scale circulations. The work also evaluates the capability of long-integration high-resolution atmospheric modeling and explores the model uncertainties from different models, domain sizes, and physical parameterizations of subscale processes in the model. The first part of the key findings is the spatial variations in the seasonality of precipitation over the TP. Three distinct precipitation regimes were found: winter peak in the western TP, early summer peak in the eastern TP, and late summer peak mainly in the southwestern TP. The winter peak regime is the most robust region with a relatively constant extent in time, while the boundary between the other two regimes varies on an interannual time scale, especially in the central TP. The variations in the boundary are associated with combined changes in summer monsoons, westerly jets, and other large-scale systems. In terms of changes in large-scale circulations, there is a positive trend in the occurrence of summer-type wind patterns. Additionally, while westerly jets were previously thought to mainly influence the winter precipitation, we found that variations in the jets can have a dominant role in changing the precipitation patterns during the transitions seasons as well. Another finding is that a long-term integration of a high-resolution meteorological model improves upon the state-of-the-art global ERA5 reanalysis, with significantly reduced wet bias over the TP by simulating weaker low-level southerly winds. The findings in this dissertation enhance our understanding of the TP precipitation patterns and associated atmospheric processes, particularly large-scale circulations. Moreover, the positive evaluation demonstrates the potential of high-resolution modeling in simulating precipitation and related atmospheric processes, thereby providing valuable insights into what control the precipitation changes over the TP in the past and potentially in the future.
Observing and Modeling Precipitation in the Tibetan Plateau region - from large-scale processes to convective storms
(2023-02-20) Kukulies, Julia
Climate change in mountain regions has far-reaching societal impacts such as increased risks for natural hazards and water scarcity that may affect billions of people in the downstream regions. Precipitation changes play a critical role in these impacts due to their effects on river runoff and flooding. However, these changes remain hard to predict due to uncertainties in climate models and a lack of reliable observations. This dissertation aims to enhance the understanding of precipitation and its underlying large-scale and mesoscale processes in the Tibetan Plateau (TP) region, one of the most extensive and vulnerable mountain regions in the world. More specifically, the dissertation combines gauge measurements, satellite observations, reanalysis data, and high-resolution model simulations to investigate present-climate characteristics of clouds and precipitation over TP and its downstream regions. A key outcome is a data set of large storms, so-called mesoscale convective systems (MCSs), based on two decades of high-resolution satellite observations of clouds and precipitation. This data set is used to study MCS characteristics and their relation to large-scale atmospheric circulation systems and water vapor transport. Satellite observations reveal that MCSs are important precipitation producers in the river basins surrounding the TP, while convection over the TP occurs in a more scattered manner with significantly less precipitation. In addition, satellite observations are used to evaluate kilometer-scale simulations of MCSs. The model simulations capture the general spatial pattern and magnitude of MCS-associated precipitation but show also systematic biases in MCS frequencies in some regions south and east of the TP. It was found that interactions between large- and mesoscale processes affect the formation and evolution of MCSs over the TP and its downstream regions. The results identify several processes, e.g. interactions between the TP and the mid-latitude westerly circulation, that may drive future precipitation changes and need to be realistically represented in future climate model projections. As such, this dissertation constitutes a step towards reliable projections of climate change in the TP region.
Impact of climate warming on Arctic plant diversity: phylogenetic diversity unravels opposing shrub responses in a warming tundra
(2022-10-13) Scharn, Ruud
The Arctic biome is at significant risk, with recent observations suggesting that climate change is warming the Arctic nearly four times faster than the global average. Last decade, evidence from experimental warming studies and observations of ambient warming over time shows how increasing air temperature in the Arctic has led to changes to arctic vegetation, and encroachment of trees and shrubs into the tundra. Thus, this amplified Arctic warming is threatening biodiversity, changing vegetation patterns, and thawing permafrost with implications for carbon and nutrient dynamics. These are one of the main concerns of observed plant biodiversity changes (except the loss of biodiversity itself) as they feedback on the global climate through their effects on carbon cycling, albedo, and ecosystem energy balance. Studies of Arctic biodiversity have reported responses in either taxonomic, functional, or phylogenetic diversity, though phylogenetic has so far been understudied in the Arctic. These different measures of quantifying biodiversity will vary in their explanatory value and can have complementary value when looking at the implications of vegetation changes. The overall aim of this thesis is to deepen the knowledge of the effect of ambient and experimental climate warming on taxonomic, functional, and phylogenetic aspects of plant diversity within and between communities. In Latnjajaure (northern Sweden) I used a long-term passive warming experiment using open-top chambers, which include five distinct plant communities. The communities had distinct soil moisture conditions, leading to community-specific responses of the plant growth forms (deciduous shrubs, evergreen shrubs, forbs, and graminoids) and phylogenetic dissimilarity. Moist communities tended to decrease in soil moisture, which drove similarity to dryer, more nutrient-poor communities. Warming significantly affected growth forms, but the direction of the response was not consistent across the communities. Evidence of shrub expansion was found in nearly all communities, with soil moisture determining whether it was driven by deciduous or evergreen shrubs. These changes are expected to affect climate feedback as the dry, evergreen-dominated heath community, has slower carbon cycling. This slowdown in carbon cycling is at least partially due to the evergreen shrubs whose material is harder to decompose than most other arctic vegetation. As the studied communities are common in the region, it is likely that future warming will drive community shifts in the tundra landscape. On a Pan-arctic dataset of warming studies, I explored the effect of scaling abundance weighting as well as the importance of deeper against shallow nodes in the phylogeny on warming response and its interaction with soil moisture and site temperature in the tundra biome. For all metrics, we looked at both plot level (α-diversity), and the difference between plots (β- dissimilarity). We show that β-dissimilarity is more sensitive to warming than α-diversity metrics. Furthermore, we show that sensitivity to abundance and phylogenetic weighting depends on local soil moisture conditions. In conclusion, the combined use of taxonomic, phylogenetic, and functional diversity measures enhances the quality of our assessment of the implications of arctic vegetation response to warming.
Outdoor heat in urban areas - Model development and applications
(2022-05-10) Wallenberg, Nils
Heat waves and high outdoor air temperature can lead to heat stress with negative implications for human health and wellbeing such as heat stroke, heat cramps, dehydration and in extreme cases death. The urban population is at higher risk of such outcomes because of the generally warmer urban climate. Daytime outdoor thermal comfort is substantially affected by short- (solar) and longwave (thermal) radiation, i.e. mean radiant temperature (Tmrt). The aim of this thesis is to deepen the knowledge of radiant conditions in complex urban areas and how such knowledge can be utilized in modelling of Tmrt and thermal comfort of humans. The overall aim is examined in three parts. The first part examines the effects of anisotropic (non-uniform) estimations of sky diffuse shortwave radiation and longwave radiation in the SOlar and LongWave Environmental Irradiance Geometry model (SOLWEIG) and how these influences Tmrt of humans in outdoor urban environments, compared to isotropic conditions. The results show that anisotropic sky diffuse shortwave radiation and longwave radiation are important in estimations of Tmrt. The circumsolar and horizon regions irradiates more diffuse shortwave radiation when the sky is anisotropic, which increases radiant load mainly in sunlit areas. Anisotropic sky longwave radiation increases with zenith angle, reaching its maximum at the horizon, resulting in higher Tmrt in open areas where the horizon region is visible. The second part focuses on outdoor thermal comfort of preschoolers in Sweden in the present and future climate using SOLWEIG. It is concluded that two thirds of preschool yards in Gothenburg have 50% or more of their yard area exposed to strong heat stress. Heat stress in preschools lead to drowsy, tired and overheated children, with negative consequences for the pedagogical activities, forcing teachers to ensure that children stay cool on the expense of education. Heat stress days are expected to increase in the future, potentially exacerbating already existing heat related issues. However, with abundant tree shade heat stress is limited, both in the present and in the future. In the third part optimized locations for trees to mitigate excessive Tmrt with regards to the shading effect of trees is analyzed. Tree positions depend on tree size and what time of day when shading is required. The results of this thesis highlights the significance of realistic models, importance of applied studies to identify heat related problems and how such problems can be mitigated.
Impact of climate variability on dynamic groundwater storage in mid- to high latitude countries
(2022-04-07) Nygren, Michelle
Climate change will alter the hydrological cycle, potentially changing dynamic groundwater storage and increasing groundwater drought risk. Climate influences groundwater storage directly via changes in groundwater recharge, but groundwater drought responsiveness further depends on groundwater system characteristics. The aim of this thesis is to increase our understanding of how climate variability and groundwater system characteristics influence groundwater storage, in mid- and high latitude countries. To address this aim, groundwater, precipitation and temperature data from Sweden and Finland between 1980 and 2010 was evaluated. Different hydroclimate regimes were compared to seasonal and inter-annual groundwater level fluctuations. Furthermore, the influence of groundwater system characteristics on groundwater drought responsiveness was assessed by analysing precipitation and groundwater level anomalies from Sweden, Finland and the Lower Fraser Valley (Canada). Correlation analysis between groundwater drought responsiveness and selected environmental properties was applied on Swedish data. The main findings of this thesis are, first, that between 1980 and 2010, groundwater recharge became decreasingly driven by snowmelt in spring. Instead, recharge became increasingly influenced by winter rain and high evapotranspiration rates in spring. As a result, dynamic groundwater storage significantly decreased across the region, particularly in Finland. Second, inter-annual groundwater level trends, covering the same period, did not correspond to trends of increasing winter snowmelt and rainfall. Groundwater level trends instead showed stronger similarity to trends in wet days, i.e. frequency of days with precipitation. Furthermore, groundwater trends corresponded better to trends in the frost-free season, compared to trends found in the frost season. Third, variability in groundwater drought responsiveness could be partly explained by environmental properties, such as sediment type (sand, silt and till), groundwater level depth, climate and atmospheric teleconnections. These findings suggest that within this century, annual groundwater recharge will decrease in the study areas, due to the projected increase in temperature and precipitation. However, this also depends on the effect of decreased ground frost on winter infiltration, and the balance between precipitation and evapotranspiration. Finally, the need for a holistic approach in groundwater drought characterisation is made apparent by the influence of climate and atmospheric teleconnections on groundwater drought responsiveness.
Nitrogen Losses from a Clay-rich Soil used for Cereal Production in south-western Sweden
(2021-11-24) Wallman, Magdalena
Addition of fertiliser nitrogen (N) in crop production increases yields and protein contents, but all is not taken up by the crop. Instead, some of the N is lost to air and waters, contributing e.g. to climate change, stratospheric ozone depletion, eutrophication and acidification. There is a need for a holistic perspective on different types of N losses, and also to include yield quantity and quality in the assessment of different mitigation options and treatments. This thesis combined the study of nitrous oxide emissions and N leaching with measurements and analysis of yields in five fertiliser treatments in cereal production. The fertiliser treatments were control (no fertiliser N added), mineral N as ammonium nitrates at two different rates (recommended and 50 % higher than recommended) and two organic N sources (biogas digestate and pig slurry). The plant available N input in organic fertilisers was between the two mineral N input rates. In the three years studied, the gap between N input and N in yield was always larger in the higher mineral N treatment, biogas digestate and pig slurry treatments than in the recommended mineral N treatment. Still, it was only the higher mineral N treatment that had significantly greater N leaching than the control, in two of the three years studied. The relatively low leaching in the organic fertiliser treatments, despite high N surpluses, appears to be an effect of ammonium fixation and adsorption to negatively charged clay particles. Emissions of nitrous oxide from the recommended mineral N treatment were close to the control, while all the three treatments with larger N surpluses had significantly higher emissions than the control. In the higher mineral N treatment, the great nitrous oxide emissions were associated with high nitrate concentrations in the drainage water. This was not the case in the biogas digestate and pig slurry treatments, and it could not be concluded whether the high emissions were driven by the addition of N, of degradable organic matter or a combination of both. However, a laboratory study on freeze-thaw related nitrous oxide emissions in the treatments with recommended mineral N rates and pig slurry indicated that the organic matter had a stimulating effect on nitrous oxide fluxes. For both N leaching and nitrous oxide emissions, post-season N losses dominated the annual budget. In relation to yield, N leaching was approximately equal from all fertilised treatments, while nitrous oxide emissions were lowest from the recommended mineral N treatment and greater for the higher mineral N, biogas digestate and pig slurry treatments. This study illustrates that, even if some circumstances, like high N access and wet conditions, in general increase the risks of both N leaching and nitrous oxide emissions, these two pathways of losses do not always go hand in hand. In this study, the discrepancy in responses was mostly an effect of ammonium fixation/adsorption and input of organic matter influencing the two pathways differently.
Ample Rare Elements: A Geochemical Anomaly in the Earth's Crust at Norra Kärr
(2021-11-18) Sjöqvist, Axel Stig Leo
The Norra Kärr alkaline complex in southern Sweden (58°06’N, 14°34’E) is a classic occurrence of agpaitic rocks, which contains a large mineral deposit of rare-earth elements (REE), Zr, and Nb. The complex consists of different varieties of agpaitic peralkaline nepheline syenite that are defined by the occurrence of Na-rich Zr–Ti silicate minerals that contain volatiles F and Cl, including members of the rinkite, catapleiite, and eudialyte groups. The eudialyte-group minerals in Norra Kärr contain different ratios of light to heavy REE across the lithological domains. The magmatic age of the alkaline complex, which is poor in common chronometric minerals, was determined at 1.49 ± 0.01 Ga (2σ) by U–Pb dating of zircon that formed during alkali metasomatism (fenitisation) of the surrounding 1.8 Ga granite. The 176Hf/177Hf isotopic ratio of this metasomatic zircon is different from Hf isotopes in the granite, but is identical with the Hf isotope composition of Lu-poor eudialyte from the alkaline complex. The relatively highly radiogenic composition of the Hf isotopes is consistent with a mantle source for the agpaitic magma. New radiometric dating methods were developed. These allow precise in situ measurements of isotope ratios of the Rb–Sr and K–Ca as well as Sm–Nd systems in K-rich and Nd-rich minerals, respectively. Three varieties of alkaline rocks in Sweden were dated by the in situ Rb–Sr method. Biotite Rb–Sr cooling ages in the region east of Norra Kärr are approximately coeval with the emplacement of the alkaline rocks. The complex has been affected by metamorphic overprinting. The foliated and folded fine-grained nepheline syenite is frequently cross-cut by coarse-grained eudialyte- rich pegmatoids. One eudialyte crystal with primary zoning from a pegmatoid was pre-characterised by SEM BSE imaging and in situ chemical analysis by LA-ICP-MS, including full REE composition and precise Sm/Nd ratios. Sampling at a resolution of <200 μm by micromill provided a sufficient Nd aliquot for routine high-precision ID- TIMS Sm–Nd isotope analysis. Eudialyte crystal growth was dated at 1144 ± 53 Ma (2σ) in the undeformed pegmatoid vein, about 350 million years after the magmatic event. The pegmatoid is suggested to have formed by low-temperature partial melting of the peralkaline nepheline syenite host at the margin of Sveconorwegian orogeny. The agpaitic rocks were produced from a magma that formed by extensive fractional crystallisation of an alkali basaltic parental magma. The concentrations of highly enriched incompatible elements in the most differentiated nepheline syenite may indicate 98 % crystallisation of the parental magma.
Sedimentology and Geomorphology of Glacial Landforms in Southern Sweden
(2021-02-26) Peterson Becher, Gustaf
Ice sheets are disintegrating due to global warming. One factor controlling ice-sheet behavior is the processes active beneath the ice sheet. In particular, processes connected to glacial meltwater drainage are essential to understand ice-sheets behavior in a warming climate. Investigating sediments and geomorphology of drainage systems below ice sheets is complicated; however, formerly glaciated regions are easily accessible. These regions display landforms and sediments formed by the processes at the ice-sheet bed. Glacial landforms were mapped in the south Swedish uplands, an area that makes up a large part of the former south-central part of the Scandinavian Ice Sheet. This region was deglaciated during the Bølling-Allerød warm period, before the Younger Dryas cold event. During the Bølling-Allerød, large amounts of meltwater were derived from ice sheets to the world's oceans. In the form of detailed digital elevation models, new datasets have made it possible to map formerly glaciated regions in unprecedented detail and pinpoint locations for detailed sedimentological work. The map produced is the first comprehensive inventory of glacial geomorphology produced for the south Swedish uplands. This mapping discovered several new features that are added to the plethora of landforms already known, including radial hummocks tracts interpreted to be tunnel valleys, glaciofluvial meltwater corridors, and a new V-shaped hummock referred to as murtoos. Hummock tracts within the area demonstrate a heterogeneous hummock morphology. As previously mapped, a lobate band of hummock tracts can be traced through southern Sweden. However, the hummock tracts also display a clear radial pattern of hummock corridors associated with ice flow. Based on the geomorphological and sedimentological analysis, the radial pattern of hummock corridors are interpreted as tunnel valleys or glaciofluvial meltwater corridors and is suggested to reflect strong meltwater activity at the bed of the ice sheet. The V-shaped hummocks (murtoos) are argued to be a new and distinct subglacial landform with a morphology related to overall ice flow. Based on ice-sheet scale distribution, geomorphological analysis, and sedimentological studies, a formational model is hypothesized. The model is driven by variations in the subglacial hydrological system connected to repeated influx from supraglacial meltwater to the ice-sheet bed within the distributed system. Tunnel valleys, glaciofluvial corridors, and murtoos are all proposed to be formed in the subglacial hydrological system. The formation of these landforms indicates intense melting at the ice-sheet surface, and this is clearly associated with times of climate warming. The landform connection can be illustrated as a times-transgressive landform system, where murtoos are suggested to form first, followed by TVs, GFCs, and finally, eskers.
Changes in near-surface winds across Sweden over the past decades - Observations and simulations
(2020-11-19) Lorenzo, Minola
Driven by a combination of anthropogenic activities and climate changes, near- surface terrestrial winds displayed a large decrease in their magnitude in the past decades, named “stilling”, and a recent recovery in their slowdown. Understanding how wind has changed and identifying the factors behind the observed variabilities is crucial so that reasonable future wind scenarios can be constructed. In this way, adaptation strategies can be developed to increase society’s resilience to the plausible future wind climate. This is particularly important for Sweden, which is largely vulnerable to changes in mean wind speed conditions and to the occurrence of extreme winds. Therefore, this thesis investigates past variations in near-surface winds across Sweden and explores the mechanisms behind their variabilities and changes. This is done by using the first homogenized dataset of in-situ observations and by analyzing current simulations of wind gusts. Results show that, during the past decades, both observed mean and gust wind speed underwent nonlinear changes, driven by the dominant winter variability. In particular, consistent with the stilling-reversal phenomena, the significant stilling ceased in 2003, followed by no clear trend afterwards. The detected stilling-reversal is linked to large- scale atmospheric circulation changes, in particular to the North Atlantic Oscillation, and the intensity changes of extratropical cyclones passing across Sweden. The comparison with reanalysis outputs reveals that, in addition to the large-scale interannual variability, changes in surface roughness (e.g. changes in forest cover) have most likely contributed to the observed wind change across Sweden. Moreover, this thesis finds that current regional climate models and reanalyses do not have adequate skills in simulating past wind gusts across inland and mountain regions. Major improvements are achieved when the elevation differences are considered in the formulation of the gust parametrization and the convective gust contribution is adjusted according to the observed climatology. The presented work advances the understanding of how surface winds change in a warmer climate at high midlatitudes and improves the model forecasting of wind gustiness over Sweden.
Towards prediction in ungauged aquifers – methods for comparative regional analysis
(2020-05-12) Haaf, Ezra
Hydrogeological investigations and in particular groundwater resource assessments are strongly reliant on understanding the factors controlling groundwater level dynamics. However, historical records of measured groundwater levels are often scarce and unevenly distributed in space and time. This irregularity of measurements, combined with hydrogeological systems with heterogeneous properties and unclear inputs and driving processes, leads to the need for systematic methods for prediction of groundwater in poorly-observed (ungauged) groundwater systems. In this thesis, methods of comparative regional analysis are presented to estimate groundwater level dynamics at ungauged sites based on similarity of groundwater system response and climatic and non-climatic characteristics. In order to carry out comparative regional analysis, methods were developed and compared for measuring similarity of groundwater system response based on entire (Paper I) and on features (Paper II) of groundwater levels time series. The relationship between similar groundwater response and groundwater system characteristics are evaluated further by identifying groups of similar sites using similarity-based classification (Paper I-III). Finally, climatic and physiographic system characteristics are identified that can be linked to groundwater dynamics aided by regression analysis and conceptual models (Paper IV). They can therefore serve as a basis for prediction in ungauged aquifers (Paper V). The thesis presents novel methods for regional analysis of groundwater resources that can be used to link groundwater dynamics to groundwater system characteristics. It demonstrates the strong potential of the presented methods and ways forward for prediction of groundwater dynamics in ungauged aquifers.
Tropical cyclone induced extreme wind, rainfall, and floods in the Mekong River Basin
(2020-04-27) Chen, Aifang
Increasing magnitude and frequency of climate extremes under global warming are threatening the socioeconomic development in many parts of the world. The Mekong River Basin (MRB) is a good example for how climate extremes can affect society, as the transboundary MRB has experienced hydroclimate changes and fast socioeconomic development during the past decades. The MRB is a flood-prone area with high flood induced mortality, where heavy monsoon rainfall and tropical cyclones (TCs) landfall are the two main determinants of floods. This thesis focuses on change in TCs and their associated impacts on extreme wind, rainfall, and floods in the MRB. Findings from this thesis provide our knowledge and understanding of TCs and their impacts, which are needed to mitigate potential consequences of global warming in the MRB and other areas facing similar challenges. Employing reliable precipitation data, this thesis finds that TC induced rainfall plays a minor role in the annual mean precipitation in the MRB. But TCs are crucial to the occurrence of extreme rainfall events, especially at the eastern lower basin, where TCs can induce floods along their tracks. TC induced floods amount to 24.6% of all flood occurrence in the lower riparian countries. TC induced floods cause higher impacts on human mortality and displacement rates than the average of floods induced by all possible causes do. Moreover, future projection shows increases in the future TC intensity under the Representative Concentration Pathway (RCP) 8.5 scenario. Overall, this thesis reveals that climate extremes, such as TC associated rainfall and floods, can substantially affect society, in terms of high TC induced extreme rainfall and great human mortality and displacement rates caused by TC induced floods; and the projected future intensified TCs indicate increasing TC risks.
The Nitrogen Cycle in Soil – Climate Impact and Methodological Challenges in Natural Ecosystems
(2018-08-31) Björsne, Anna-Karin
Nitrogen (N) is a fundamental element for life, and limiting in many terrestrial ecosystems. In non-N-fertilized ecosystems, the N inputs can be low, and the nutrient availability for plants is determined by the internal cycling of N. The N availability might alter with different factors, such as climate change, forest management practices, and tree species. Soil N cycling is investigated using stable isotopes, where the activity in the soil can be monitored over time. The overall aim of this thesis is to increase the understanding of the N cycle in natural and semi-natural ecosystems and the environmental factors important for nutrient cycling. The results show that all sites investigated in this thesis had higher NH4+ turnover than NO3- turnover. The mineralization rates were highest in the site with the lowest C:N ratio, and the lowest mineralization rates and the highest C:N ratio in the spruce forests, which demonstrate the importance of organic matter quality on gross N transformation rates. The N cycle responses to combined climate treatments were generally lower than responses to single climate treatments. For some processes, we observed opposing responses for eCO2 as single and main treatment compared to the plots receiving the full treatment. This point to the importance of conducting multifactor climate change experiments, as many feedback controls are yet unknown. Gross nitrification was lowered with fertilization in a northern boreal forest, which is an interesting result in the light of the very low nitrous oxide (N2O) emissions from the investigated site, despite heavy annual fertilization of 50–70 kg ha-1. Moreover, the results from an experiment with soil of common origin and land history showed generally higher gross mineralization, immobilization and nitrification rates a beech stand compared to a spruce stand. The beech stand had also higher initial concentration of nitrate (NO3-) which indicates a more NO3- based N cycling. Finally, numerical modeling together with 15N tracing is an improvement for simultaneously determining free amino acid (FAA) mineralization, peptide depolymerization and gross N mineralization rates, compared to analytical solutions. This thesis confirms that N cycling in natural ecosystems is governed by the properties of the soil, vegetation and climate, but also that the experimental set-up strongly affects the outcome of the experiment. In turn, this affects the potential of doing reliable experiments, especially in ecosystems where the external inputs of N are very low. The thesis also highlights some methodological challenges that lie in the future of N cycling research.
Road climate studies with emphasis on road surface temperature variations and hoar frost risk
(2018-05-24) Hu, Yumei
An effective road transportation system is a key enabler for national and global economic growth. In the wintertime, the presence of snow and ice on road surfaces reduces road surface friction and can result in serious injuries and significant economic loss. Accurate road weather forecasting, focusing on when and where road slipperiness will occur, improves the efficiency of winter road maintenance activities, thus helping to ensure the safety and mobility of road users. The purpose of this thesis is to increase the understanding of the spatial distribution of road surface temperature (RST) and hoar frost, a common and hazardous form of road slipperiness, across a road network. The thesis consists of two parts. The first part models the influence of geographical parameters on RST distribution during times of day when most traffic uses the road network, using thermal mapping data recorded at times of day other than the latter part of the night. Using thermal mapping from times of day other than the latter part of night makes it possible to assess the feasibility of using road weather related measurements from in-car sensors (Floating Car Data) to model RST distribution. The second part of the thesis characterises the risk of hoar frost on winter roads, across the whole of Sweden, and investigates how that risk changes in a warming climate. The results show that using thermal mapping from times of day other than the latter part of night, can improve the modelling of RST variation across a road network. Cumulative direct short-wave radiation model that takes shading into account can explain up to 70% of the observed variation in RST and is recommended for daytime RST modelling, due to its simplicity. However, the influence of sky-view factor (ψs) should not be ignored in the early morning, late afternoon, or when the influence of cloud is significant, because diffuse and long-wave radiation under such conditions play a more important role. Geographical parameters combined with thermal mapping from times of day other than the latter part of night can be used to build repeatable geographical models and explain up to 67% of the variation in RST distributions. The results suggest it might be inappropriate to use air temperature (Ta) from Floating Car Data to reflect the influence of geographical parameters on RST distributions. The influence of altitude and the urban heat island might be reflected in the relationship between Ta and geograhical parameters. However, the influence of other parameters, such as shading and (ψs), is less easy to deduce using Ta readings from Floating Car Data. The results in the second part of the thesis show hoar frost is mainly caused by warm air advection in northern Sweden and radiative cooling in southern Sweden. Over the past few decades, increased RST has reduced the risk of hoar frost in the south of Sweden (south of 59°N), whilst increased relative humidity has increased the risk of hoar frost in central Sweden (59°N ~ 65°N). The strengthened winter North Atlantic Oscillation is the main cause for the changes. A warming climate also influences how frequently the conditions that lead to the formation of hoar frost occur. The relative frequency of hoar frost occurring because of warm air advection has significantly decreased, while the relative frequency due to radiative cooling has significantly increased, mainly due to the weakened temperature gradient between land and ocean in a warming climate.
Nitrous Oxide Production in Agricultural Soil – Linking Biogeochemical Pathways and Drivers
(2018-05-09) Schleusner, Philipp
Nitrous oxide (N2O) is a long-lasting and potent greenhouse gas responsible for depletion of stratospheric ozone. As the atmospheric N2O concentration reaches all-time highs, emission variability in space and time still leaves unresolved questions. The aim of this thesis is to improve our understanding of the origin of N2O and its main drivers from the largest anthropogenic source: agricultural soil. Therefore, we investigated agricultural soil from long-term trial field sites in the laboratory and used 15N-enriched tracers in two main approaches: partitioning of the sources of N2O production and quantification of the gross rates of microbial processes competing for ammonium (NH4+) and nitrate (NO3-). The varying relative contribution of NH4+, NO3- and organic nitrogen (Norg) to N2O emission highlights the influence of site-specific factors apart from the field management. Without fertilizer, Norg was the dominant N2O source related to high carbon (C) contents and C:N ratios. High N2O emissions were caused by increasing contributions of nitrification and denitrification, which was drastically stimulated by mineral nitrogen (N) fertilizer. In addition, N fertilizer application more than doubled N2O production from native non-fertilizer N compounds, which provides evidence for primed N2O production. By using the Ntrace model, we quantified gross rates of N cycle processes that compete for substrates and regulate N2O production. In the long term, cropping systems can shift the balance between denitrification and dissimilatory nitrate reduction to ammonium (DNRA), which determines the fate of NO3- in soil. A perennial cropping system that maintains high SOM contents and C/NO3- ratios has shaped the microbial community of dissimilatory nitrate reducers leading to higher N retention by DNRA and lower N2O emissions. By applying selective inhibitors, we were able to quantify the specific activity of archaeal and bacterial nitrifiers competing for NH4+. While both can coexist and be equally active in agricultural soil with low N supply, bacteria outcompeted archaea with increasing NH4+ concentration, which can be responsible for higher N2O emissions as well. This thesis illustrates how human action drives N2O emission from agricultural soil in a variety of ways since field management affects N cycle processes in the short- and long-term. While N fertilizer application strongly stimulates N2O production from added- and native N sources, long-term field management can change the soil properties, which shifts the abundance of microbial communities and thereby alters the N cycle processes responsible for N2O production.
Tree rings and climate in Scandinavia and Southern Patagonia
(2017-11-30) Fuentes, Mauricio
The present knowledge of temperature variability during the past millennium has been greatly improved due to an increasing availability of reconstructions made based on paleoclimate proxies, such as tree-rings. These improvements however, do not suffice to provide a coherent representation of the past climate at local to regional scale at higher latitudes. The reasons, are mainly due to the poor spatial density of the networks and the little understanding of how microsite variability affects the signal stored in the varied tree-ring proxies. Fennoscandia and Patagonia are strategic locations for studies on past climates, and were chosen to extend and improve the existing dendrochronology networks. This work also aimed to provide high quality improved chronologies with skills to reconstruct primarily temperature, with attention to the effects of microsite conditions and large scale atmospheric and oceanic patterns. Using Pinus sylvestris L., two temperature reconstructions were made: a local from the west central Scandinavian mountains extending 970 years using the blue light intensity absorption from tree-rings, and a regional built on ten chronologies extending through the Scandinavian mountains using density and blue intensity information from the tree rings. Additionally, a gridded reconstruction was made on the latter. In Patagonia six Nothofagus betuloides and one Pilgerodendron uviferum chronologies were developed and analyzed. These contained limited and non-statinary information on temperature and precipitation, probably on account of microsite conditions. Chronologies at both study sites were proven to contain information of large-scale atmospheric and oceanic patterns. In Fennoscandia, Atlantic Multidecadal Oscillation and Summer North Atlantic Oscillation in addition to volcanic forcing modulate significantly local to regional climate and therefore tree-growth. In Southern Patagonia in turn, tropical and subtropical sea surface temperatures seem to affect tree-growth. While relationships between tree-growth with the Southern Annular Mode were found on years of extreme growth, they were marginal and non-stationary when tested with index at interannual scale. Patterns of spatial correlations with sea level pressure further suggest these links. Moreover, the Pacific sector of the Southern Ocean, specifically the areas of the Amundsen and Bellingshausen Seas are indicated to have an unprecedented importance to the growth dynamics of the southernmost forest in the world. The new chronologies developed in the study areas possess potential to be used on studies of climate evolution at higher latitudes taking into account that microsite conditions affect the climate signal recorded in the tree-growth.

Browse

Recent Submissions