Remotely sensed thermal information applied to urban climate analysis Rita Pongracz * , Judit Bartholy, Zsuzsanna Dezso Department of Meteorology, Eotvos Lorand University, Pazmany st. 1/a, H-1117 Budapest, Hungary Received 5 November 2004; received in revised form 21 June 2005; accepted 22 June 2005 Abstract Urban heat island (UHI) effects on the ten most populated cities of Hungary, including the Budapest agglomeration area, were analyzed using remotely sensed data. Day- and night-time surface temperature time series observed by sensor MODIS on satellite Terra were used to determine UHI intensities. UHI intensity was defined as the difference in spatially averaged surface temperatures between urban and surrounding rural pixels. Spatial structures of UHIs were determined and compared for different seasons and macrocirculation conditions. Ó 2005 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Urban heat island effect; Surface temperature; Satellite Terra; Sensor MODIS; Carpathian Basin 1. Introduction According to United Nations estimations about half of the world population live in urban areas at the end of the second millennium, and the ratio will tend to in- crease in the future (IOM, 2000). The high population density and the socio-economic conditions induce in- tense industrial activity. Consequently, consumption of energy and other raw materials are increasing. In or- der to find potential mitigation strategies that facilitate the urban population to adapt to new environmental conditions urban heat islands and other climatological impacts of urbanization should be investigated. In this paper the UHI effects for the Budapest agglomeration area and the nine largest cities of Hungary are com- pared. A new approach has been applied, namely, satellite images serve as a basic tool in the present analysis. Urban heat islands have been investigated using sa- tellite imagery for three decades. The early studies eval- uated coarse resolution satellite data (7–8 km per pixel) (Rao, 1972), and their methods to calculate the surface temperature from the spectral observations were very simple (Carlson et al., 1977; Price, 1979). These inves- tigations in the 1970s and 1980s concluded that satellite measurements can be applied to detect the UHI effect in case of clear conditions. The thermal differences be- tween urban and rural areas appear even in case of rel- atively small towns (Matson et al., 1978). Traditionally, UHI analysis (Howard, 1833; Oke, 1982) uses air tem- perature data observed at standard height (1.5–2 m above the ground), while remotely sensed information is available at ground-level. The maximum of the UHI intensity occurs a few hours after sunset using the air temperature data, while it can be detected dur- ing day-time in case of using satellite images (Vuko- vich, 1983; Roth et al., 1989). Nowadays, the main 0273-1177/$30 Ó 2005 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2005.06.069 * Corresponding author. Tel.: +36 137 22 945; fax: +36 137 22 904. E-mail addresses: prita@elte.hu (R. Pongracz), bari@ludens.elte.hu (J. Bartholy), tante@nimbus.elte.hu (Z. Dezso). www.elsevier.com/locate/asr Advances in Space Research 37 (2006) 2191–2196