Influence of geographical factors and meteorological variables on nocturnal urban-park temperature differences - a case study of summer 1995 in Goteborg, Sweden

This study deals with the magnitude of influence of various geographical fa ctors and meteorological variables on the air temperature difference betwee n a park and a built-up area (Delta Tu-p). The statistical analysis focuses on the time of nocturnal maximum Delta Tu-p in summer in Goteborg, Sweden, during May to October 1995. The geographical factors include sky view fact or, height above sea level and distance from the park border. The meteorolo gical variables considered include wind, cloud cover and type, global radia tion, air temperature, subsurface temperature and humidity. Principal compo nent analysis is used to identify temporal and spatial patterns of the temp erature anomaly along a transect across the built-up area and green area. T he first principal loading is found to explain 71% of the total variance. I t represents a kind of mean pattern and depicts the dominant distribution o f the anomaly along the transect, which is interpreted as being created by the differences in surface characteristics. Distance from the park border a ccounts for 86 % of the spatial variation in air temperature. The magnitude of this pattern is mainly modulated by the average wind speed and the aver age cloud index, i.e. cloud cover and type, from sunset until the time of i nterest, i.e. 27 and 13 % respectively of the variation in Delta Tu-p can b e explained by these variables. Subsurface temperature and urban-park vapou r pressure difference can explain minor parts of the variation in Delta Tu- p. The wind direction affected both the spatial pattern and the magnitude o f Delta Tu-p. The influence on magnitude under different wind directions wa s probably caused by the difference in relative sizes between the warm buil t-up area and the colder park and suburban area.