Featured Thesis Figure

Paleo-climatic influence on flat-topped carbonate platforms in Lac de Joux, Switzerland

Based on previous seismic and bathymetric analyses of the Lac de Joux, Switzerland, this study addresses the nature of isolated flat-topped carbonate platforms in 1 to 5 m water depths that are not attached to the shore.
By reviewing the bathymetry (panel A) and the seismic stratigraphy (panel B), we interpreted the platforms as structures on nuclei formed by past glaciations. Indeed, glaciers in the Joux Valley shaped retreating moraines into drumlins (1). These geomorphic analyses were followed by sediment analyses that investigated the sediments covering these glacial features: due to the change of temperatures from the Pleistocene to the Holocene, carbonate precipitated and accumulated onto the platforms (3). Visible on the seismic sections, windward progradation (3b) of the platform succeeded accumulation (3a) as the sediment supply exceeded the accommodation space below wave base. Our analysis shows that these carbonates were chemically precipitated and bio-induced by algae, mainly charophytes. Additionally, periods or events of clastic spills into the region of the platforms were confirmed by the higher Ca/K ratio and Fe content. Together with the changes in sedimentary calcite concentration, this allows us to state that paleo-climatic changes in the environment surrounding the platforms influenced them directly.

Figures 18 and 19 from the master thesis by Eléonore Perret.

Read more about student research

Vertical particle export during the last glacial cycle in Southern Indian Ocean sediment cores

The oceanic sediment core MD12-3394 was retrieved in the Southern Indian Ocean. This region is characterized by a very high biological productivity in the surface ocean. Accordingly, the particle accumulation rate on the sea floor is very high. For this Thesis, the cycles of Marine Isotope Stage 3 (MIS 3) were analyzed. These cycles were rapid climate fluctuations between 35 and 60 kyr BP. The Figure shows: (A) the barite flux in the MD12-3394 core, which is a proxy for export production; (B) the atmospheric CO2 concentration reconstruction from the EPICA Dome C ice core (Bereiter et al., 2015), correlated with climate variations; and (C) the lithogenic flux, representing the amount of terrestrial material brought to the core site.
During past ice ages, large atmospheric CO2 concentration variations were closely linked with biological productivity and eolian dust input in the Southern Ocean. It is apparent from this figure that whenever the biological productivity was increased, the atmospheric CO2 concentration increased simultaneously, and the lithogenic flux decreased. This implies that the biological productivity at this location was not a control on atmospheric CO2 concentration; as we would have expected an increased primary production to consume CO2 and transfer it to the depth, therefore reducing its concentration. Additionally, the decrease in lithogenic flux, concomitant with the increased biological productivity, indicates that eolian dust fertilization is not a factor.
As a result, the only process capable of increasing biological productivity at the ocean surface in this situation is an increased upwelling. Increased upwelling would strengthen the biological pump, but reduce its efficiency. The net outcome is a stronger biological productivity, and an outgassing of deeply sequestered CO2. This points to atmospheric CO2 regulation mechanisms during the small scale variations within the glacial cycle, similar to those identified for large glacial to interglacial CO2 variations. Master thesis by Antoine Thévenaz.

Read more about student research

Homogenised monthly series from the meteorological diaries of Johann Rudolf von Salis-Marschlins 1781-1800

The meteorological diaries of Johann Rudolf von Salis-Marschlins contain a rich collection of climatological data. Within the studied years of 1781-1800, well over 10’000 pressure and temperature measurements, more than 4’000 observations of phenological phases, and close to 2’000 descriptions of precipitation events can be found. So far, the Marschlinian diaries have played a minor role in historical climatology, which is mainly due to reported inaccuracies of the used instruments. With the construction and homogenization of a monthly temperature series (upper panel), pressure series, and precipitation depth totals, this master thesis sheds new light with robust, quantitative information on local climate during this early-instrumental period. Further potential of the Marschlinian diaries is evaluated by means of an analysis of snow cover data and observations of phenological phases (see 12 selected phases in bottom panel, cf. Figures 3.13. and 4.4., pages 74 and 112, from the master’s thesis by Markus Grimmer).

Read more about student research

Swiss cantonal strategies for adaptation to climate change

Using a Qualitative Comparative Analysis, this thesis contributes to answering the question why a Swiss canton has developed a strategy in order to politically tackle climate adaptation. Such a strategy is the dependent variable (y-axis in the Figure, label ADAPT). A score of 1 means that a canton has elaborated an adaptation strategy (e.g. canton of BE). A score of 0.67 stands for cantons that plan to elaborate an adaptation strategy but have not done so yet (e.g.  canton of VD). Scores below 0.5 indicate that adaptation strategies are neither planned nor elaborated. In total, sufficient explanations (so-called solution paths, displayed on the x-axis) as to why cantonal adaptation strategies are formulated are: (1) defining climate adaptation as a legislative objective, (2) emphasizing strong mitigation policies together with the presence of a left-wing minister, and (3) emphasizing mitigation policies together with the existence of a high problem perception (shown here, label MIT*ALPS*PERC). Climate adaptation and mitigation, however, do not always occur in parallel: defining adaptation measures does not automatically imply that mitigation measures are also given high priority. Master thesis by Eva Wieser.

Read more student research

Simulating the potential range of shallow landslides

Shallow landslides pose a considerable danger to humans and infrastructure due to their sudden triggering and high velocity. In this master thesis, the CLIMADA2 model was implemented to simulate the risk for shallow landslides. The model is designed to be globally applicable with minimum data requirements and incorporates an algorithm to determine possible source areas and flow paths of shallow landslides. The flow path is assessed by an algorithm adapted from Flow-R which consists of a flow direction, inertia and friction model. Its output grid can be interpreted as a point’s, spatial relative, probability to be reached by a shallow landslide (see Figure). A comparison of modelled with observed lengths of shallow landslides revealed that the flow path algorithm is not suitable to model single shallow landslides. However, the model captures the overall distribution of slide lengths and is expected to be skillful for modelling extreme (long) slides. (Figure from the master thesis by Thomas Rölli, 2018)

Read more student research

Strategic interaction between countries can hinder incentives to invest in climate-related technologies

Climate-related technology can be an option to keep global temperature increase below the 2° C target set by the Paris Agreement.
This master thesis tests whether strategic interaction (interaction between n>2 players, who inter alia maximise their respective utilities, and where the players’ payoff depends on the actions of the other players) hinders or fosters countries (players) to invest in four climate-related technologies, (i.e., abatement AB, energy efficiency EE, adaptation AD and low-carbon technology LC) in a non-cooperative setting.
It is shown that strategic interaction hinders the incentives to invest in abatement technology, fosters the incentives to invest in energy efficiency and adaptation technology, and can both foster and hinder the incentives to invest in low-carbon technology. This is true for all countries. We conclude that this could partly explain the low level of current mitigation measures worldwide.
Specifially, the strategic interaction effect (the product of the marginal damage and the total derivative of the aggregate emissions of all the other countries with respect to a technology parameter, see Figure) hinders the incentives to invest in AB and LC technologies and fosters the incentives to invest in EE and AD technologies for the global top-5 CO2 emitters. Alos, the direct effect (the partial derivative of a benefit, cost, or damage function with respect to a technology parameter) always outweighs the indirect, i.e, the strategic interaction effect. Hence, none of the countries has an incentive to invest in a less efficient AB or LC technology due to strategic reasons. However, in the case of symmetrical countries, a country would always prefer to invest in a less efficient abatement technology due to strategic reasons.  This implies that if the countries are homogeneous enough, they might want to commit to lower mitigation levels in order to pass the burden of mitigation to the other countries.  In the context of international climate negotiations, this implies a free-riding strategy on abatement technology.. (Figure from the master thesis by Anna Kulakovskaya, 2018)

Read more student research

Glacier-friendly weather?

In this thesis, a number of historical air temperature and pressure measurements from European stations were used to answer this question with regards to the Lower Grindelwald Glacier. To assess potential north-to-south shifts of storm tracks, a 2–6-day bandpass Lanczos filter was applied to the pressure data (see Figure). It was found that a run of cold summer seasons between 1840 and 1847 and many cold and wet fall seasons between 1836 and 1853 were linked to a strengthening and a southward shift of the storm tracks. We argue that this contributed strongly to the last growing phase of the Lower Grindelwald Glacier in the mid-19th century. (Figures 17 and 19, pages 58 and 60, from the master thesis by Julian Flückiger)

Read more student research

Recurving tropical cyclones

Tropical cyclones are known for their severe direct impacts. Some of them undergo extratropical transition when they recurve (from north-westerly to easterly directions) over the Atlantic and move poleward into a midlatitude environment. They have a potential for high impact weather further downstream, over Europe.

During extratropical transition, the ascending air and enhanced moisture transport causes strong latent heat release and inject air with low potential voriticity into the upper troposphere (upper panel of the Figure). This in turn accelerates the upper level jet and amplifies its waviness.  This meridional amplification of the extratropical flow over the Atlantic is important for the formation of extreme precipitation events over Europe (lower panel of the Figure).

This thesis provides the first climatological assessment of the effect of recurving North Atlantic tropical cyclones on precipitation extremes over Europe. We find a significant increase in precipitation extremes over Europe in three out of four major configurations of the atmospheric flow, and between 30 and 72 hours after the interaction onset. The response is however sensitive to the jet configuration at the moment of the interaction.

Difference between current and future species richness (shade indicates number of species) in western Switzerland for a moderate scenario, i.e. a combination of +2° C mean winter temperature and -20% intensive pasture.

Species richness in a warmer climate

Agricultural intensification and climate change are among the main drivers for biodiversity changes.
In this thesis, a two-part hurdle model was implemented to predict present and future plant richness in grasslands of the western Swiss Plateau. An extensification of grasslands (>=20% of pastures area from intensive to extensive) under warmer conditions (+ 2° C in mean winter temperature) is found to produce higher species richness (i.e. up to 70 % more species) in the study area until 2050.
The southern Broye valley, the pre-alpine zones and today's high-diversity areas (yellow to green shades) would profit most from less intense pasture management combined with higher winter temperatures. Conservation measures would therefore be most effective in these regions. (Figure from the master thesis by Luca Bussani)

Read more student research

Drivers of Inter-Annual Variability in Wood Density

Dendroclimatology utilizes a number of tree-ring parameters to reconstruct past climates. This thesis investigates the mechanisms that drive variations in wood density of eight Pinus cembra cores, using an image analysis software with very high resolution.
A biplot of the first two principal components (PC) shows the relationships between relevant anatomical features of tree rings (shown are abbreviations in the Figure). The first PC (x-axis; explaining 47% of the variance in the original dataset) can be seen as a measure of  the cell wall thickening phase. The second PC (y-axis; 19% explained) is a good measure of mean and maximum density. The vector length is equal to the variance of the variables. Furthermore,  the distance between vectors refers to the similarity between variables. In short,  latewood width (LWW; highlighted) is strongly correlated to density parameters (MDCWT & MDCWA), i.e., closely resembles mean density.
This suggests that latewood width can serve as a surrogate for density if such measurements are not attainable. Understanding how anatomical features of tree rings are related to density parameters helps to better understand the mechanisms that drive inter-annual variations in wood density. (Figure 34, page 55, from the master thesis by Lisbeth Haberbauer)

Read more student research

Reconstruction of historical flood levels of the river Aare in Aarau

Over the past centuries, the Swiss city of Aarau has been recurrently affected by floods. In this thesis, historical floods are assessed by means of administrative protocols, chronicles, maps, paintings, and newspaper articles. Between 1400 and 1900, a number of 39 flood events were dated (not shown). Prior to 1700, floods occurred significantly earlier in the year than after 1700, a seasonal pattern that is in accordance with observations of rivers in Germany. Water levels of ten of these events were reconstructed for the first time in this thesis (orange dots for events prior to 1852, the bars indicate probable ranges). Data after 1852 are adjusted gauge readings. Local river regulations were rather ineffective, and recurring conflicts between involved political levels delayed effective measures until the 1850s. On a regional scale, the upstream Kander deviation in 1714 and the Jura water correction 1868-1891 had a great impact on the river system in Aarau. They substantially deepened the riverbed and thus decreased the danger of floods (effect approximated by the two black dotted lines). (Figure 17, page 85, from the master thesis by Mauro Bolzern)

Read more student research

This decade's solar photovoltaic emergence: a cross-sectorial investigation

Solar photovoltaic technology has been available since the 1950’s however the technology has not been widely applied until the beginning of this decade.  In this thesis, the paramount factors for this boom are investigated using Qualitative Comparative Analysis of the leading promoting countries, i.e. with at least 10 gigawatts of installed solar photovoltaic capacity.

The analysis revealed three potential pathways. The first positive pathway (Path 1 in the Figure; dot sizes represent importance) includes the cases of Japan and the United States. They are representative of cases that have "Ability" and* "Resource Intensive Populations" and* "Potential to decarbonize their electricity and heat production sectors". The second pathway (Path 2), represented by China and Japan, is similar to the first in the sense that they have the same parsimonious solution (taking only the large circles into consideration). The third and final pathway (Path 3) is indicative of a more sustainable path taken by European countries such as, Germany and Italy. This more sustainable pathway is highlighted by the presence of "Kyoto Commitments" and* the "Inability to rely on nuclear power production in the future" and* "Potential to decarbonize" and* "Ability".

Path 3 is in essence the most desirable because it encompasses emission reduction pledges under international climate negotiations. In contrast, Path 1 and 2 seem to be primarily fueled by large, resource intensive populations and growing economical necessities. (Figure 15, page 50, from the master thesis by Simon Steffen).)

Read more student research

Changes in the risk of spring frost damage for grapevines due to climate change
A case study in the Swiss Rhone Valley

Global warming does not only cause the growing phases of plants to start earlier, it also leads to a shift in the average day of year of latest frost days. Depending on the magnitude of these changes, as well as on the corresponding variances, it is not clear if risk for spring frost damage will increase or decrease. Focusing on the Swiss Rhone Valley, future risk according to the SRES A1B scenario was modelled by combining two locations, four frost indices, twelve phenology models and 16 climate model chains. The solid lines indicate the yearly means of the frost indices (i.e. the probability of a frost day after budburst (BBCH09), p(T.n<0°C), the frequency of frost days after BBCH09, f(T.n<0°C), the temperature sum of daily minimum temperature below 0 °C after BBCH09, ∑(T.n<0°C), and the temperature sum of daily mean temperatures below 2 °C after BBCH09, ∑(T.0<2°C)), the day of year (DOY) of the last frost day and of BBCH09. The shaded areas indicate the range of +/- one standard deviation around the yearly means. The broken red lines visualize the mean trends for the period 2001 to 2050. The average risk for spring frost damage is predicted to slightly decrease. This may support winemakers in their decisions regarding future grape varieties and frost damage prevention measures.
(Figure 12, page 66, from the master thesis by Michael Meier)

Read more student research

Quinoa yields w.r.t. temperature and precipitation (Lampa, Arapa, and Chuquibambilla stations, Peru, years 1964 - 2012)

The potential value of seasonal climate forecasts for allocating agricultural land is estimated in this thesis. Therefore, a theoretical model was developed and applied to the region of Puno in Peru. The application relies on using statistical climate data and simulated yields for quinoa and potato crops - the Figure presents yield simulations for quinoa depending on two climatic indicators, i.e. the seasonal precipitation sum and the minimum temperature during the flowering stage. The analysis shows that the expected revenue can be increased by 4.66 % when key decisions are made with seasonal forecasts, compared to a scenario without seasonal forecasts. The positive value indicates the potential of integrating high-quality seasonal forecasts into decision-making when allocating agricultural land to specific crops.
(Figure 4, page 24, from the master thesis by Anita Frehner)

Read more student research

Mean runoff of the river Thur in a present-day versus a pre-industrial climate

The thesis assesses the influence of anthropogenic greenhouse gas emissions on temperature, precipitation and runoff of the river Thur in Switzerland. To achieve this, thousands of Global Climate Model simulations with both present-day (A2000) and pre-industrial (A2000N) climate conditions are bias-corrected (from raw to corr; see Figure) and fed into a hydrological model for the river Thur. Higher mean runoff in winter and spring is formed in the present-day scenario (red colors) compared to the pre-industrial scenario (blue colors). This is mainly caused by the combination of increased precipitation and higher temperatures in winter, resulting in less snow accumulation in the present-day scenario. Therefore, more liquid water is available in the hydrological model, leading to enhanced runoff. In contrast, the present-day simulations exhibit lower runoff in summer and autumn than the pre-industrial simulations. This may be caused by the higher temperatures in the present-day scenario which enhance evapotranspiration and thus decrease the amount of water entering the hydrological model. These findings may support decision-makers in climate-related risk and adaptation management.
(Figure 5.7, page 41, from the master thesis by Regula Mülchi)

Read more student research

Weak points along the main rivers of the Bernese Oberland (Switzerland).

Weak points are locations along a river bed where the channel capacity is frequently exceeded during periods of high river discharges. Hence, weak points indicate potential focii for flood protection measures. Technically, weak points are defined as cross sections of the river bed where the bank-full discharge (channel capacity) has a flood recurrence period (HQ) between 30 and 100 years (red to yellow lines). Whereas specific river sections had been analyzed in practice so far, entire watersheds of the Bernese Oberland (Switzerland) were investigated in this thesis. The highest numbers of weak points (relative to the number of measured cross sections) are found for the Simme, Weisse Lütschine and the Hasli-Aare rivers. The good news is that frequently exceeded channel capacities (<= HQ30) are located along unpopulated areas. However, the protection aim of HQ100 along populated areas is not hold along parts of the Weisse Lütschine and the Simme, and neither along the Aare within the cities of Thun and Bern. These findings provide valuable information for both national and regional watershed administration.
(Figure 3.40, page 87, from the master thesis by Danielle Huser)

Read more student research

Seasonal total precipitation near Mt. Kenya, interpolated from gauge measurements during the Long Rains (March-April-May) in 1977.

The seasonal precipitation pattern in Central Kenya is highly influenced by the peculiar topography of the area, especially by Mt. Kenya (contour lines; bottom right quadrant). In this thesis, interpolations for seasonal and annual totals are obtained from rain gauge measurements (filled squares) using a combined approach of multiple linear regression with topographic predictors and ordinary kriging of residual precipitation. For the boreal spring rainy season, highest amounts of precipitation are found for the south-eastern slopes of the mountain.
Recent changes in agricultural practices and population growth have triggered conflicts between different water users, as economy and food security highly depend on rain-fed agriculture and river water discharge. In this context, the provided spatial information about rainfall can be used for water ressource allocations, for hydrological studies or to monitor trends over space and time.

(Figure 5.4, page 35, from the master thesis by Noemi Imfeld)

Read more student research

Cumulative influences of various drivers on the total CO2 emissions in the US from 1997 to 2013.

During the economic recession, between 2007 and 2009, the CO2 emissions dropped by approximately 10%, where the production structure as well as the consumption volume played the most important roles in said decline. The influence of the fuel mix was more or less continuously negative over the entire time period and sums up to the strongest negative influence on the CO2 emissions from 1997 to 2013. The fuel mix describes changes in energy use from coal to gas, from coal to renewables, from oil products to renewables, etc.

(Figure 2, page 51, from the master thesis by Marius Schneider)

Read more student research