Abstract
In this study, the spatial patterns of relative air humidity and its relation to urban, geographical and meteorological factors in the city of Zaragoza (Spain) is discussed. We created a relative humidity database by means of 32 urban transects. Data were taken on different days and with different weather types. This data set was used to map the mean spatial distribution of urban dry island (UDI). Using stepwise multiple regression analysis and Landsat ETM+ images the relationships between mean UDI and the main geographic-urban factors: topography, land cover and surface reflectivity, have been analyzed. Different spatial patterns of UDI were determined using Principal Component Analysis (Varimax rotation). The three components extracted accounted for 91% of the total variance. PC1 accounted for the most general patterns (similar to mean UDI); PC2 showed a shift of dry areas to the SE and PC3 a shift to NW. Using data on wind direction in Zaragoza, we have found that the displacement of dry areas to the SE (PC 2) was greater during NW winds while the shift to the NW (PC 3) was produced mainly by SE winds.
Highlights
Urban areas are spaces where anthropic transformations of the environment are greatest
General Spatial Patterns of the urban dry island (UDI) and Relationships among UDI and Surface Reflectivity, Elevation, and Vegetation Cover The standardized cartography of each of the measurement days allows comparison between the different maps by converting absolute values into standard deviations with respect to the average, and permits a mean map to be drawn up showing the UDI configuration in Zaragoza and the city’s outlying areas (Figure 5)
This study analyses the general characteristics of relative air humidity in a medium-sized city in the Mediterranean region, using a database created by means of urban transects and digital cartography, spatial regression techniques and Geographical Information System (GIS)
Summary
Urban areas are spaces where anthropic transformations of the environment are greatest. One of the best-known and most-studied consequences is the formation of what are called urban heat islands, and another of the observed effects is the modification of relative air humidity, meaning that the atmosphere of cities is normally drier than the rural atmosphere. A few qualitative associations with land-use data have been reported: Henry et al (1985) analyzed the statistical relationships of the urban-rural distribution of humidity with the various types of Relative air humidity in Zaragoza, Spain materials and land uses of the city of Lawrence, in Kansas. Robaa (2013) carried out a similar study on the Greater Cairo region, searching for a link between variations in relative air humidity and urban, suburban and rural areas. No quantitative relationships have been established between humidity patterns and urban and geographical factors based on an extensive data set
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