Wildfire | EPFL Graph Search

A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a bushfire (in Australia), desert fire, grass fire, hill fire, peat fire, prairie fire, vegetation fire, or veld fire. Some natural forest ecosystems depend on wildfire. Wildfires are distinct from beneficial human usage of wildland fire, called controlled or prescribed burning, although controlled burns can turn into wildfires. Modern forest management often engages in prescribed burns to mitigate risk and promote natural forest cycles. Wildfires are often classified by characteristics like cause of ignition, physical properties, combustible material present, and the effect of weather on the fire. Wildfire behavior and severity result from a combination of factors such as available fuels, physical setting, and weather. Climatic cycles wi

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

Development of the Jungfraujoch UV DIAL Lidar to Observe the Vertical Ozone Distribution in the Context of Stratosphere Troposphere Exchange and Long Range Transport

Marcel Bartlome

Tropospheric ozone is a climate relevant greenhouse gas, as well as an atmospheric pollutant. Its abundance in the troposphere is mainly governed by the influx of stratospheric air masses and the photochemical production due to anthropogenic and biogenic ozone precursors. Precise model simulations and measurements are needed to assess the exact impact of these sources onto the total tropospheric ozone content. In the latter case, vertical tropospheric ozone profiles are commonly obtained from in-situ balloon-borne soundings. These routine observations are performed with a maximum frequency of several measurements per week. Therefore, they are not suited to resolve the rather fast changes in the tropospheric ozone concentration. However, accurate vertical ozone profiles with temporal and spatial resolutions suitable for studying those changes have been produced for decades using remote sensing by means of the ozone UV differential absorption lidar (DIAL) technique. The main goals of this thesis aimed to address some of the unresolved problems of the ozone origin and evolution in the upper troposphere and lower stratosphere and were: to develop an UV DIAL for the observation of the vertical ozone distribution in the free troposphere and at the tropopause region. to perform experimental measurements of vertical ozone profiles in the free troposphere and the tropopause in order to assess the ability of the ozone UV DIAL to observe fast variations in vertical ozone distribution caused by stratosphere-troposphere exchange (STE), long range transport, and advection from the boundary layer. to assess the feasibility of systematic ozone profile retrieval by the ozone UV DIAL technique from the High Altitude Research Station Jungfraujoch (HARSJ, 3580 m ASL, 7°59'2''E, 46°32'53''N). The HARSJ was chosen for the experiment because of its location, which allows ozone UV DIAL measurements of the tropopause region without perturbation of the lower troposphere. Furthermore, previous atmospheric studies have shown that because of the station's location, the upper tropospheric data taken at the HARSJ can be regarded as representative for central and western Europe. During the first two and a half years of the thesis project the ozone UV DIAL was designed and built. The ozone UV DIAL transmitter is based on a commercial, fourth harmonic Nd:YAG laser. The on- (284 nm) and off- (304 nm) ozone UV DIAL wavelengths are produced by stimulated Raman scattering in high-pressure nitrogen. The receiver uses the existing astronomical Cassegrain telescope (76 cm in diameter) at the HARSJ. Spectral separation of the backscattered ozone UV DIAL wavelengths is carried out by a polychromator based on an concave imaging diffraction grating. The entire ozone UV DIAL detection unit is integrated into the existing long-range multi-wavelength polychromator box optically coupled at the Cassegrain telescope's rear end. With the current design, the ozone UV DIAL system provides hourly averaged ozone profiles reaching from 6 km to 12 km ASL with a vertical resolution better than 400 m at 6 km ASL and 1000 m at 12 km ASL. The relative statistical error of the profiles is 10% at 12 km ASL. The experimental measurements started in the spring of 2008 but were interrupted several times because of serious laser failures. As a first step of the experiment, the ozone UV DIAL profiles were compared to balloon borne ozone profiles taken by electrochemical concentration cell (ECC) sondes. The sondes were launched by the Swiss Meteorological Institute – Payerne (SMI, 46°49'N, 6°56'E, 491 m ASL) situated 80 km in northwestern direction of the HARSJ. The ozone UV DIAL and the sonde measurements were taken quasi simultaneously. The relative differences between the ozone UV DIAL and the sonde profiles were found to be below ±25% in a horizontally homogeneous atmosphere. The intercomparison has shown that the ozone UV DIAL is capable to accurately reproduce the vertical ozone distribution. Intercomparison with vertical ozone profiles taken in the vicinity of the HARSJ by an airplane-borne UV-photometer confirmed the performance of the ozone UV DIAL. Time series with duration of up to 21 hours were taken in order to study the time evolution of tropospheric events characterized by elevated ozone concentrations. As a result of these measurements three events, demonstrating different processes have been identified. In the first case an air layer with elevated ozone concentration was observed in the altitude range between 6 and 7 km ASL. The lower than 10% relative humidity and the time evolution of this layer allowed to determine its stratospheric origin. The observations are in a good agreement with the EURopean Air Pollution Dispersion (EURAD) model. The model predictions also agree with the elevated ozone concentration measured by the UV-photometer of the National Air Pollution Monitoring Network (NABEL) operated at the HARSJ. The evolution of an ozone-enriched layer in the tropopause region was followed for 21 hours during the second case study. The time evolution, the ECC data, and the EURAD model predictions suggest the possibility of a short filamentation process developing at the tropopause region. The measurements of the third event were made according to a prediction of STE forecasted by a dynamical model developed at the ETHZ. A short living enhancement of the ozone concentration has been observed at an altitude of about 9.5 km ASL. There are two possible explanations for this event. The first one could be a short living reversible STE event. A second explanation is a possible long-range transport of ozone and ozone precursor rich air from the forest fires in the Athens region suggested by the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) backward trajectories. However, the available information does not allow to make a definite conclusion. The ozone UV DIAL has been built successfully and has shown its ability to observe fast variation in vertical ozone distribution with high accuracy and precision. In combination with additional water vapor and temperature lidar observations and supported by model forecasting, this system could become a powerful tool for the improving of the understanding of upper troposphere and lower stratosphere ozone related processes. However, to allow future systematic observations the ozone UV DIAL will need an essential upgrade to resolve the problems related to the long preparation time, and the limited by technical reasons time of observation.

EPFL2010

Interannual variability in tropospheric ozone and its precursors

Symeon Koumoutsaris

Tropospheric ozone (O3) is a harmful pollutant and an increasingly important green-house gas. Tropospheric O3 distributions are determined by complex and non-linear interactions between photochemistry and transport processes. The first objective of this thesis is to examine the factors that contribute to the interannual variation (IAV) of tropospheric O3 and related compounds, such as carbon monoxide (CO), for a period of 19 years (1987-2005), with a focus over the northern mid-latitudes. A series of long-term measurements, including ozonesondes, groud-based sites and satellites, are interpreted with a global chemical-transport model (GEOS-Chem) and a number of sensitivity simulations are performed to quantitatively assess the relative contribution of individual processes to the IAV of O3 and CO. We first assess the capability of the model to reproduce O3 and CO IAV. We find that the model is able to reproduce reasonably well many of the observed features of the O3 and CO IAV. The model however, fails to reproduce the observed variation in O3 in the northern mid-latitudes during the first half of the 1990s (negative anomaly in 1991-1993 followed by an upward trend in 1993-1996) which is likely due to an inadequate representation of stratospheric dynamics and stratospheric O3 concentrations in the model. This study has demonstrated that the principal drivers of O3 and CO IAV are meteorology and emissions. We examine in particular the 1998-1999 period. A large anomaly in O3 was observed at several sites over Europe and is fairly well reproduced by the model. Different processes are found to contribute to this long-lasting anomaly. The first period (spring 1998) was largely influenced by the strong preceding El Niño episode of 1997. El Niño Southern Oscillation (ENSO) affects the stratosphere-troposphere exchange (STE) and the Asian pollution export, through a change in convective activity and a strengthening of the subtropical jet. North American pollution export was also enhanced through an increase in temperature and in photochemical activity. During the second period (summer-fall 1998), the O3 budget over Europe was influenced by both boreal wildfires and Asian pollution. Finally, the O3 anomaly during the third period (spring 1999) was affected by enhanced biomass burning emissions in Southeast Asia. We further noticed that a significant correlation exists between the Southern Oscillation Index (SO1) in fall and the European tropospheric O3 column in the following spring (R= -0.65, N=19), throughout the period from 1987 to 2005. In other words, increasing tropospheric O3 column is seen over Europe the following spring of an El Niño year. In the second part of this thesis, we used inversion methods to derive monthly NOx, emissions from GOME and SCIAMACHY space-based retrievals of nitrogen dioxide (NO2) columns for a period of 10 years (1996-2005). We calculated emission trends over the highly industrialized regions and large cities around the globe. Decreasing emissions were found in the U.S. and Europe. However, negligible or even positive trends were seen in urban areas in northeastern U.S. (e.g. Boston) and southern Europe (e.g. Lisbon, Istanbul) which are most probably due to increasing motor vehicle NOx, emissions. Furthermore, a slowdown in the decreasing trend in NOx, combustion fuel emissions over North Europe has been noticed after 2000 and especially in 2003-2004. This is probably related to a slowdown in the decrease in road transport emissions. Increasing trends, on the other hand, have been found in the combustion fuel NOx, emissions over east China (8.3% year-1), due to the fast industrial and economical development of China. In addition, we found an upward trend in soil NOx, emissions which may be related to the increasing use of fertilizers in the northeastern part of the country. Finally, we examined the influence of using two different retrievals of NO2 columns on the resulting a posteriori inventories. The inversion was carried out twice for the year 2000, using two different retrievals, one from Dalhouse/SAO and one from BIRA/KNMI. The two resulting inventories were found to correspond well globally, but show important differences (more than 60%) at specific times and regions.

EPFL2008