This paper addresses the issue of usefulness of selected spatialization techniques for the characterization of an urban heat island (UHI). Five interpolation methods (including both deterministic and stochastic methods or their combination) -namely: inverse distance weighting (IDW), regularized spline with tension (RST), ordinary kriging (OK), multiple linear regression (MLR) and residual kriging (RK) -were evaluated for their ability to estimate air temperature in Wroc8aw, Poland, during 7 cases of the UHI. Spatial interpolation was performed based on time-adjusted air temperature data gathered by mobile measurements. Additional explanatory variables for multidimensional spatialization methods (MLR and RK) were developed based mainly on the land-use map and Landsat thematic mapper (TM) images. Statistically significant predictors were selected using a stepwise regression procedure. Parameters for optimal interpolation were chosen by cross-validation (CV) of results. The CV technique was also used to compare results obtained with the different algorithms together with evaluation of errors (e.g. root mean square error, RMSE; mean absolute error, MAE) and visual examination of the final maps. The least plausible maps, both in terms of error statistics and visually, were obtained with the IDW method. Inside the convex hull of sample points, the OK and RST techniques were characterized by simplified but acceptable air temperature surfaces. The MLR method expressed the land-use background of the UHI, even outside the convex hull, but distorted results when the process tended towards non-stationarity, e.g. due to wind influence. The most accurate results of the UHI spatialization were obtained with the RK technique.
KEY WORDS: Spatialization · Spatial interpolation · Urban heat island · GIS · Wroc8awResale or republication not permitted without written consent of the publisher Clim Res 38: 171-187, 2009 This means that the isothermal pattern of an UHI is generally concentric but also strongly dependent on the spatial arrangement of the land-use types that produce local variation. The UHI shape can therefore differ from city to city and may be described as 'amoebic' (e.g. Seoul, South Korea; Park 1986) or 'multicellular ' (e.g. 1ódź, Poland;K8ysik & Fortuniak 1999).Although knowledge on the origin and consequences of UHIs has gradually increased in recent years, the accurate estimation of the UHI spatial structure, which is often needed by town planners, is still one of the most important problems. In addition, air temperature determines numerous aspects of the urban environment and data on its spatial structure is an essential input for various modelling studies (e.g. dispersion of air pollutants). However, sampling sites in the monitoring system are often sparse, limiting the application of interpolation techniques. Data gathered at meteorological stations can be supported by mobile measurements to solve data inadequacy, although some data-time adjustments are needed (Duckworth & Sandberg 1954, Kuttler ...