Sven Lindqvist

The influence of green areas on nocturnal temperatures in a high latitude city (Göteborg, Sweden)

The air temperature pattern in three urban parks and their surrounding built-up areas was studied over a one and a half year period in Goteborg, Sweden. The measurements were made at mobile and permanent stations on nights with clear skies and light winds. The maximum temperature difference found between a park and a built-up area was 5.9°C (summer), and the extension of the cool park climate into the built-up area was over 1100 m from the park border. Both the extension and the magnitude of the temperature difference depended on the size of the park and the distance from the park border. The green area cooled at a faster rate than the built-up area, although there were large variations within each area. At the rural station, located at an open site, the cooling was less than at the open part of the green area. Differences in sky obstruction between the sites explained some of the variations in cooling and temperature. However, the relationship between the urban-park temperature difference and sky view factor was not statistically significant.

Spatial and temporal variability of nocturnal summer frost in elevated complex terrain

Abstract This paper presents an investigation of summer night temperatures as influenced by a sharply undulating terrain, with a view towards the consequences of summer frost on forest regeneration in thermally marginal areas. The focus is on the presentation of the spatial distribution of monthly mean frost (MMF) in an elevated frost prone area, located approximately 100 m below the timber-line in the southern Swedish Scandes. The MMF is defined as the lowest temperature over a 4 h period at each location on each frost occasion in the study area which is then summed up and averaged for each month of the growing season. Geostatistics (kriging) is used for modelling the MMF distribution in June, July, August and September, 1994. Kriging is essentially a weighted moving average technique which aims to estimate the temperature at a given site based on observations at neighboring sites. The results from modelling using two different sampling strategies are compared over a 90,000 m 2 clear-felled area. A lower density of 18 observations is used for sampling on a fixed grid and a higher density of 29 observations aims to cover the spacing of distinct terrain features in the area. The investigated region is characterized by a local topography with sharp vertical variations, i.e. ‘basin and knob’ terrain. The estimated frost patterns are evaluated in relation to a set of typical pre-defined forms in such terrain. It is found that the spatial distribution of low temperatures corresponded well with local terrain forms and that frost is experienced during each month of the vegetative period. However, there are obvious differences in frost intensity and duration. The single most important factor for explaining the frost patterns during the peak of the growing season is the difference in radiative cooling due to the surrounding local terrain. Variations in the cooling rate of up to 6°C h −1 are recorded between sites that are partially screened from solar radiation and sites that are well exposed. Wind shelter provided by the immediate surroundings of a site is also found to have a significant influence on the near-surface temperature. Maximum differences of 3–5°C are maintained between sites with various degrees of shelter at a mean wind speed of 1.5 m s −1 . In June, August and September, drainage of cold air is identified as another important process affecting the distribution of frost. It is suggested that the drainage flow is a shallow gravitational cold air flow of a strictly localized nature.

New evidence of desertification from case studies in northern Burkina Faso

ABSTRACTCase studies on desertification in northern Burkina Faso, in the Western Sahel, using satellite-aided ground navigation technology, have shown that a noticeable environmental degradation to...

Local Climatological Modelling for Road Stretches and Urban Areas

The local climate is described by using models coupled to form larger units. The work has a geographical approach in which the surface properties are the most important parameters. One example is from the project on a local climatological model for prediction of air and road surface temperatures along road stretches, where five geographical factors are primarily considered. The other is from an urban climatological project and deals with the relation between land use, urban structure and local climate.

STUDIES ON THE LOCAL CLIMATE IN LUND AND ITS ENVIRONS

Some results from a series of measuring trips by car are discussed. The measuring trips were under- taken at three-hourly intervals. For more comprehensive mean value calculations, fixed stations with recording instruments have been used. The monthly mean tempera- ture differences for every other hour of the 24-hour period between the various stations have been studied. The thawing after a snowfall has been measured on the ground and evaluated from aerial photographs.