Fallen temperature effects at green patches of urban residential areas and analysis of its influence factors

The environment temperature and relative humidity at 130 green patches of 21 urban residential areas in Shanghai were investigated at high temperature weather in summer, and temperature drop range at different urban green patches and its influence factors were also researched. The results show that the urban green patch has an obvious effect on falling temperature and increasing relative humidity to surrounding environment, which can improve human comfort with a temperature falling of 2. 6 °C, relative humidity increasing of 8. 3% and human comfort increasing of 0. 8 at the center of green space. The environment temperature and relative humidity have significant effects on temperature drop range of urban green patches, and the effect of environment temperature is higher than that of relative humidity. The temperature drop range has a significantly positive correlation with environment temperature (R = 0. 416) and a significantly negative correlation with relative humidity (R =0.460). With environment temperature rising and relative humidity decreasing, the temperature drop range at green space center is the biggest. Among the main structural indexes affecting temperature drop range of urban green patch, the influence of big arbor coverage is the strongest, followed by that of small arbor and shrub coverages, and with increasing of coverage, the effect of falling temperature become more and more obvious at the green space, especially at the center of green space. Also the green space type, shading state and tree species planted at urban green patches have significant effect on temperature drop range. The temperature drop range of green patches planted with big arbor is the highest (2.8 °C ), 2.0 °C with small arbor, and only 1.4 °C and 1.2 °C with arbor-shrub and shrub-herb, respectively. Using Cedrus deodara (Roxb.) G. Don and Cinnamomum camphora (L.) Presl as dominant tree species at green patches, the effect of falling temperature is the most obvious, while that of lawn is the worst. It is suggested that for falling temperature, arbor should be used as dominant structure type and shrub-herb as subsidiary type, and single lawn green type is avoided as possible to use in green design at residential areas.