Heat wave | EPFL Graph Search

A heat wave (or heatwave)), sometimes known as extreme heat, is a period of abnormally hot weather. High humidity often accompanies heat waves. This is especially the case in oceanic climate countries. Definitions vary but are similar. We usually measure a heat wave relative to the usual climate in the area and to normal temperatures for the season. Temperatures that people from a hotter climate consider normal can be called a heat wave in a cooler area. This would be the case if the warm temperatures are outside the normal climate pattern for that area. Heat waves have become more frequent, and more intense over land, almost everywhere since the 1950s. This is due to climate change. Heat waves form when a high pressure area in the upper atmosphere strengthens and remains over a region for several days up to several weeks. This traps heat near the ground. Heat waves often have complex effects on human economies. They reduce labo

A global model study of ozone enhancement during the August 2003 heat wave in Europe

The European summer of 2003 was characterised by intense heat, prolonged isolation and suppressed ventilation of the boundary layer which, combined with large anthropogenic emissions and strong fires, resulted in a build up of an unprecedentedly high and long-lasting photochemical smog over large parts of the continent. In this work, a global chemistry and transport model GEOS-Chern is compared with surface O-3 concentrations observed in 2003 in order to examine the extent to which the model is capable of reproducing such an extreme event. The GEOS-Chem reproduces the temporal variation of O-3 at the Jungfraujoch mountain site, Switzerland, including the enhanced concentrations associated with the August 2003 heat wave (r = 0.84). The spatial distribution of the enhanced surface O-3 over Spain, France, Germany and Italy is also captured to some extent (r = 0.63), although the largest concentrations appear to be located over the Italian Peninsula in the model rather than over Central Europe as suggested by the surface O-3 observations. In general, the observed differences between the European averaged O-3 concentrations in the summer of 2003 to those in 2004 are larger in the observations than in the model, as the model reproduces relatively well the enhanced levels in 2003 but overestimates those observed in 2004. Preliminary contributions of various sources to the O-3 surface concentrations over Europe during the heat wave indicate that anthropogenic emissions from Europe contribute the most to the O-3 build up near the surface (40 to 50%, i.e. 30 ppb). The contribution from anthropogenic emissions from the other major source regions of the northern hemisphere, in particular North America, tends to be smaller than those of other years. The model indicates that the large fires that occurred in that year contributed up to 5% (3 ppb) to surface O-3 in close proximity to the fire regions and less elsewhere in Europe. Biogenic volatile organic compounds (VOCs) emitted by grass and forest areas contributed up to 10% (5-6 ppb) of surface O-3 over France, Germany and northern Italy, which represents a contribution that is twice as large than that found in 2004. These results in terms of contributions from various sources, particularly biogenic emissions, should be seen as preliminary, as the response of vegetation to such extreme events may not be well represented in the model.

2007

Comparaison des caractéristiques climatiques sous couvert forestier et hors couvert

Valentine Renaud

We compared open-site and below-canopy climatic conditions from 14 different sites in Switzerland based on LWF data (Long-term Forest Ecosystem Research). The 14 sites represent different locations, orientations and elevations, from the Jura Mountains to the southern side of the Alps, composed of deciduous, coniferous and mixed forests. Meteorological measurements were carried out under the canopy at the observation plots, and in open areas outside the forest plots. We analysed air temperature during summer 2003, in connection with the exceptionally high temperatures measured during that summer and during the 11-day August heat wave. From April to October 2003, there was a significant correlation between the absolute value of temperature and the difference between open-site and below-canopy temperature: the warmer the temperature, the stronger the impact of the forest. For maximum temperature, the difference was higher in deciduous and mixed forests, especially those with beech as the dominant tree species, compared to conifer forests. For minimum temperature, the discrepancy was higher in conifer forests but, generally, the north-oriented slopes showed greater differences than the other slopes. The results are similar for a decade period of temperature analysis between below-canopy and open-field, from 1998 to 2007. We also compared below-canopy and open-field data for minimum, maximum and daily mean temperature, relative humidity (RH), maximum and daily mean photosynthetically active radiation (PAR) and wind speed (m/s) from 1998 to 2007. We analysed the forest influence on local summer and winter climate according to the forest type (coniferous, mixed, deciduous), soil type, basal area (m2/ha) and tree height (m). In summer, deciduous and mixed forests generally have the strongest impact on daytime temperatures, from 3 to 5 K cooler under the canopy, with a higher RH, up to 17%. Coniferous forests have a moderating effect on night temperatures, from 1 to 4 K warmer below-canopy, with a lower HR, from 4 to 15% less humid under the canopy. In winter, the forest lowered the day-time temperatures, from 0.2 to 5K, accordingly to the orientation and the dominant specie, and generally increased night-time temperatures, up to 6.2 K in north-oriented conifer sites. The day-time RH was enhanced in all forest types compared to open-field, from 5 to 22%, except in an open Scots pine forest, and the night-time RH was generally reduced below-canopy, especially in coniferous stands, being up to 22% less humid below-canopy in pine forests. We applied the Heat Index (HI) and the NET (Net effective temperature) index to the open-field and below-canopy meteorological data (maximum temperature, relative humidity and wind speed) in order to determine the bioclimatic potential of the different forest stands in summer from 1998 to 2007, and more specifically during the summer 2003 heat wave. We applied the NET index and the Windchill index to determine the forest bioclimatic potential for human wellbeing during winter from 1998 to 2007. In summer, generally, the bioclimatic conditions were clearly more comfortable for humans in the forest than in open-field. When the conditions came out as very hot or requiring extreme caution in open-field, they were in the more comfortable zone in the deciduous and mixed forest at hill and mountain level. This was particularly evident during the exceptionally hot summer of 2003. In winter, bioclimatic conditions were also more comfortable below-canopy, mainly due to the forest effectively reducing wind speed. In order to cope with the likely increasing frequency and intensity of heat waves, our results show and quantify the role of forests in providing a cool shelter. The results are of particular value to urban areas, where forested parks could provide an important source of relief during heatwaves. It is therefore necessary to maintain and develop the accessibility of forested areas to city dwellers. Accordingly to our sample, the most efficient ecosystems for this purpose appear to be generally the deciduous and mixed forests and more specifically the beech and beech–silver fir stands. The opposite effect was seen in mugo pine and Scots pine forests, with warmer temperatures under the canopy compared to open-site.

EPFL2010

Cost and benefits of climate change in Switzerland

Anita Frehner, Wolfgang Knoke, Dario Stocker, Philippe Thalmann, Boris Thurm, Marc Vielle, Frank Vöhringer

Understanding the economic magnitude of climate change impacts is a prerequisite for developing adequate adaptation strategies. In Switzerland, despite new climate scenarios and impact studies, only few impacts have been monetized. Our objective is to assess costs and opportunities of climate change for Switzerland by 2060, while enhancing the assessment methods. Using inputs from bottom-up impact studies, we simulate the economic consequences of climate scenarios in a CGE framework. We cover health, buildings/infrastructure, energy, water, agriculture, tourism, the spill-overs to other sectors, and international effects. Due to data constraints, significant impacts have not been quantified, e.g. for heat waves and droughts more extreme than the 2060 average climate. For the considered impacts, welfare decreases by 0.37% to 1.37% in 2060 relative to a reference without climate change. Higher summer temperatures increase mortality and decrease productivity. Contrariwise, tourism benefits from extended summer seasons. Regarding energy, increased demand for cooling is overcompensated by savings in heating.

2019

A global model study of ozone enhancement during the August 2003 heat wave in Europe

2007

Comparaison des caractéristiques climatiques sous couvert forestier et hors couvert

Valentine Renaud

EPFL2010