Climat | EPFL Graph Search

Le climat est la distribution statistique des conditions de l'atmosphère terrestre dans une région donnée pendant une période donnée. L'étude du climat est la climatologie. Elle se distingue de la météorologie qui désigne l'étude du temps dans l’atmosphère à court terme et dans des zones ponctuelles. La caractérisation du climat est effectuée à partir de mesures statistiques annuelles et mensuelles sur des données atmosphériques locales : température, pression atmosphérique, précipitations, ensoleillement, humidité, vitesse du vent. Sont également pris en compte leur récurrence ainsi que les phénomènes exceptionnels. Ces analyses permettent de classer les climats des différentes régions du monde selon leurs caractéristiques principales. Le climat a fortement varié au cours de l'histoire de la Terre sous l'influence d’une pluralité de phénomènes astronomiques, géologiques, etc., et plus récemment sous l'effet des activités humaines (réchauffement climatique). Terminologie

Toward Assessing the Sensitivity of Buildings to Changes in Climate

Sönke Frederik Horn

A building is designed for one set of typical climatic conditions. In the context of expected climate change, substantial numbers of existing and new buildings are expected to survive long enough to experience perceptible shifts in climate ‘normals’ (averages). This is problematic for predicting building performance, largely because the exact nature of climate change is hard to predict with certainty. Thus an optimal design is not only tuned to the original design conditions, but is also robust to changes in climatic conditions in the sense of a low sensitivity of its performance. To predict a building’s response to changes in typical weather, two inputs are required: weather data representing this change, and suitable metrics to compare building performance across different climate normals. This report presents initial work on a proposed method for assessing the sensitivity of new or existing buildings to climate change. This method begins with a selection of weather files to represent climate change, then quantifies a building’s passive performance in those climates using an enthalpy-based metric, and ends with a graphical analysis of the performance of the building in different climates to assess its robustness. In this report, we propose an objective performance metric based on the extent to which a building creates indoor conditions passively, i.e. without auxiliary systems. Initial work suggests that the performance assessment carried out here is reproducible and applicable for indoor environment design and evaluation in different ranges of climate change. This approach enables a comparison of building performance without the bias introduced by inherent differences in climatic conditions.

2013

Towards implementing new isotopes for environmental research:Redetermination of the 32Si half-life

Mario Aaron Veicht

The predicted climate changes on Earth will significantly impact the environment and human society. The climate patterns observed during the past centuries led to a better understanding of the driving forces for such changes. However, more studies using new, innovative techniques are necessary to broaden the knowledge on the involved processes and accomplish a reliable scientific basis for decision-makers.On this subject, radiometric dating is a well-established contemporary technique whereby various time periods (from a few years to millions of years) can be covered with this method. Notably, a dating gap exists so that the period from 100 to 1000 years (before today) is currently not covered. However, this period is of great interest, as it allows for studying and understanding environmental processes such as glacier dynamics, ocean, and atmospheric circulation. Interestingly, a potential nuclide that could fill this dating gap is available: Silicon-32 (Si-32). The problem, however, is the currently very inaccurately determined T1/2 of around 150 years so that a use for radiometric dating is hindered.Hence, the aim of the SNSF-funded SINCHRON (Si-32: a new chronometer) project, and therefore the primary goal of this thesis, concerns the re-determination of the Si-32 half-life. Previous half-life determinations were limited to using samples with low activities. To overcome the issue with the small amounts, Si-32 was artificially produced at the Paul Scherrer Institut (PSI). Subsequently, an innovative wet chemical separation system was developed to allow for the selective removal of Si-32 from an irradiated vanadium matrix. As a result, 20 mL of an ultra-pure Si-32 solution could be produced, fulfilling the desired parameters related to the half-life re-determination.Within the framework of this work, the determination of the half-life via the direct method was applied; i.e., both the determination of the number of atoms (N), in combination with the activity (A), are required. Within the SINCHRON-collaboration, several independent measurements were performed between various multinational metrological institutes. Based on the different requirements, the Si-32 solution was manufactured accordingly: (I) the solution's activity concentration was confirmed to be greater than 100 kBq/g, (II) a chemically very stable Si species was chosen, and (III) ultra-traces of S-32 were removed. Besides, (IV) solid samples for accelerator mass spectrometry (AMS) could be prepared from the stock solution, too. As a result, we are getting close to providing a new, recommended value with low uncertainty (less than 5%). Within the scope of this work, a preliminary T1/2 for Si-32 of 125 +/- 5 years has been determined. Additionally, we studied vanadium as a target material and determined the production cross-sections of Ti-44, Ca-41, and Al-26. These radionuclides are produced as by-products during the irradiation process. For the latter two nuclides, the presented data describe the very first experimental determination of the cross-section for vanadium as a target. In this context, two independent gamma spectrometric measurement systems were used for the activity determination of Ti-44, and no prior chemical separation of Ti-44 from the matrix was required. Contrarily, Ca-41 and Al-26 were successfully separated using a selective and robust chromatographic wet chemical separation scheme. The activity of these nuclides could then be determined using AMS.

EPFL2022

Prevention of forest fires in a changing climatic context in Ticino, southern Switzerland

Michael Reinhard

Switzerland is not a place commonly associated with forest fires, unlike many areas of the nearby Mediterranean Basin. However, in this Alpine country, forest fires occur every year and destroy forests that fulfil various functions, the most socially and economically important of which is protection from natural hazards. Canton Ticino is the most affected by forest fires. The protective function is of vital importance for local communities. Most of Ticino's population lives in valley bottoms, where most transportation infrastructures are built, and without forests these are vulnerable to mass flows. In Ticino, forest fires occur mostly during the winter/spring season when dry conditions occur due to low precipitation and strong Foehn events. At this time, deciduous trees have shed their leaves and there is an important seasonal accumulation of dry litter on the forest floor. Fuel load has also increased over recent decades due to the abandonment, since about 1960, of traditional agro-forestry activities that removed dead wood, dry leaves and forage grass from the forest. Fuel in the forest is particularly flammable during the dry winter and leads to very high fire risks. Climate change has contributed to increasingly fire-prone conditions over the past decades and may also have had an effect on forest composition. Most Ticinese forest fires are anthropogenically triggered and negligence is the primary cause of fires. The only natural cause of fire is lightning, which affects forests particularly during summer, when heavy storms occur. This dissertation aimed at gaining a better scientific understanding of the interactions between landscapes, humans and forest fires in the context of climate change, in order to prescribe recommendations to achieve forest fire prevention and diminish fire related risks. We focused on the mechanisms leading to forest fires and adopted an integrated approach, which necessitated the use of a variety of methods: i) climate trend analyses, ii) flammability tests using a standardised ignition apparatus and a thermo-gravimetric analyser, iii) qualitative social science methods using focus groups and semi-structured interview techniques, iv) quantitative social science methods by means of a questionnaire. The results suggest that climate has changed in recent decades with more frequent and intense fire-prone conditions. Minimum and maximum temperatures have both increased significantly and relative humidity has decreased significantly for all daily measures during fire season. The present study suggests that fire-prone conditions are likely to become even more acute. Climate also has an important impact on the composition of the forests and the state of vegetation, as well as the condition of the fuel load. The most flammable species (Castanea sativa and some laurophyllous species) tend to occur near human settlements and this is of importance for management. Some of these species are expected to increase due to climate change. People involved with the forest fire prevention system perceived the actual fire policy as generally well working and well planned, and they perceive preparedness as strong, although discussions showed that the prevention of accidental fires is not addressed by the current fire policy. Effective prevention requires accurate information about the social aspects of forest fires, which until now has not been available in Ticino. Mechanisms leading to fires are not very well understood by locals, although many people identify correctly some technical aspects of forest fires. Depth of understanding is related to geography, gender, age, profession, marital status, income and life-style. Differences between these socio-demographic groups and geographical patterns suggest that prevention needs to be better targeted and that the population cannot be treated as a homogeneous entity. We conclude the dissertation with a series of recommendations for local authorities and people involved in the forest fire policy setting. These recommendations concern climate, vegetation flammability and forest fire prevention in Ticino.

EPFL2006