Beyond intensity of urban heat island effect: A continental scale analysis on land surface temperature in major Chinese cities.

Intensity of urban heat island (UHII) is a key indicator to quantify the magnitude of UHI effect. Change in UHII, however, can be affected by change in urban or rural temperature, or both. Numerous studies have investigated the change of UHII, but how it relates to change in urban and rural temperature is poorly understood. Here we present a continental scale analysis on the change in UHII from 2000 to 2015 in 31 major cities in China, and further explored whether such change was caused by urban warming. We used time series analysis based on MODIS land surface temperature product (MOD11A2) in summer. We found: (1) A majority of the cities (25 out of 31) had an increasing trend in UHII from 2000 to 2015, among which 44% were significant, suggesting a significantly intensified UHI effects. (2) Intensified UHII does not necessarily mean deterioration of urban thermal environment, and vice versa. For the 25 cities with an increasing trend in UHII, 11 cities had a decreasing trend of LST in both urban and rural areas. Meanwhile, for the 6 cities with a decreasing trend in UHII, three had warming trend in both urban and rural areas. (3) The attribution of changes in UHII to that of urban and rural LST indicated that it is necessary to quantify the change of LST in both urban and rural areas to fully quantify the impact of urbanization on UHI effect.