At each block the three

2. Study area and methods
The study was conducted in urban Hong Kong situated at the south China coast at longitude 114°E and latitude 22°N, which lies in the humid-subtropical climatic zone strongly influenced by the Asian Monsoon system. The annual climatic pattern Skepinone-L characterized by contrasts between hot-humid summer and cool-dry winter, interspersed with mild-humid spring and mild-dry autumn. The frequent and heavy rainfalls in the wet season, running from May to September, account for most of the yearly 2400 mm precipitation. The potential evapotranspiration amounts to 1062 mm per annum [34]. In summer, the mean daily temperature is 30.2–31.4 °C, and in winter 16.3–17.9 °C. Typhoons (tropical cyclones) occasionally struck the city in the warm months to bring exceptionally strong winds and prolonged torrential rains.
Two recently-built high-rise (over 30 stories) residential blocks (Blocks 1 and 2) in a new town served as the study site. Tall buildings for domestic or commercial use are ecology common in Hong Kong. The two blocks have the same building footprint, floor plan and orientation, and lie adjacent to each other. One wing of each block with the same southeast orientation was identified for the field study. Each wing contains three apartments (Flats A, B and C) of similar floor area. The total of six top-floor apartments (Block 1: 1A, 1B and 1C; Block 2: 2A, 2B and 2C) and the respective six roofs lying above were left unoccupied for a year to conduct the experiment. The windows and doors were kept closed in the course of the study which runs from November 2011 to December 2012.