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Chinese Journal of Applied Ecology ›› 2021, Vol. 32 ›› Issue (12): 4223-4236.doi: 10.13287/j.1001-9332.202112.012

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Spatiotemporal variations of wet-bulb temperature and its impact factors of Nanjing urban neighborhood

LU Yang1,2, YANG Yi-chen3, WU Xin-ran2, WANG Lei4, WAN Zi-wen1,2, ZHENG Zhe-jun5, XU Jia-ping6, CAO Chang1,2*   

  1. 1Yale-NUIST Center on Atmospheric Environment, Nanjing University of Information Science and Technology, Nanjing 210044, China;
    2School of Applied Meteorology, Nanjing University of Information Science and Technology, Nanjing 210044, China;
    3School of Environment, Yale University, New Haven 06511, USA;
    4School of Chemistry and Materials, Nanjing University of Information Science and Technology, Nanjing 210044, China;
    5School of Agriculture, Wonsan Agricultural College, Wonsan 999093, North Korea;
    6Jiangsu Climate Center, Nanjing 210009, China
  • Received:2021-02-25 Revised:2021-09-17 Online:2021-12-15 Published:2022-06-15
  • Contact: *E-mail: chang.cao@nuist.edu.cn
  • Supported by:
    National Key Research and Development Program of China (2019YFA0607202), National Natural Science Foundation of China (42005143, 41475108), Natural Science Foundation of Jiangsu Province (BK20180796, BK20181100), and Open Research Fund of Key Laboratory of Meteorology and Ecological Environment of Hebei Province (Z201901H)

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Abstract: Global climate change and local urban heat islands enhance urban heat stress. Studies focused at the urban neighborhood scale are limited. Wet-bulb temperature represents the combined effects of both temperature and humidity, and therefore can more accurately reflect human thermal comfort. In this study, air temperature, relative humidity and geographic information of different times, seasons, and sky conditions of the Nanjing Jiangbei New Area were obtained based on mobile measurements. The spatiotemporal variation of wet-bulb temperature at the urban neighborhood scale and the effects of sky conditions, land cover and urban morphology (sky view factor, SVF) were further analyzed. The results showed that: 1) the spatiotemporal variations of wet-bulb temperature at the Nanjing urban neighborhood scale were consistent with that of air temperature. Compared with vapor pressure, air temperature played a dominant role. The extremely high values of wet-bulb temperature in this area were mostly caused by the synergy between air temperature and vapor pressure. 2) The correlation between SVF and wet-bulb temperature was significantly positive in the daytime and negative at night. An increase in the vegetation fraction could reduce wet-bulb temperature, while impervious surfaces had the opposite effect. The wet-bulb temperature significantly decreased and its spatial distribution was much more homogeneous under overcast sky conditions. 3) The horizontal scale effect showed diurnal and seasonal differences and was more sensitive to sky conditions during nighttime than during daytime. Compared with vegetation, the horizontal effect of impervious surfaces was much larger in winter than in the other two seasons. The horizontal scale effects of vege-tation and impervious surfaces on wet-bulb temperature were similar to those of air temperature. These results could provide effective scientific support and a theoretical basis for improving and optimizing the thermal environment of urban neighborhoods, as well as alleviating urban heat stress.

Key words: urban neighborhood scale, wet-bulb temperature, sky view factor, vegetation fraction, impervious surface fraction