Abstract: With the acceleration of urbanization, the problem of urban surface heat island effect is gradually becoming prominent. In order to study the impact of urban spatial expansion and socio-economic development on the heat island effect, based on five periods of Landsat remote sensing images from 2000 to 2020, the surface temperature of Hefei City and Nanchang City, China, is inverted using the radiative transfer equation method. The heat island effect in the study area is divided into 4 grades using normalization method, the temporal and spatial evolution characteristics of the heat island effect in the two cities are analyzed and studied, and then the influence factors of the heat island effect intensity are comprehensively analyzed using geographic detectors. The results show that: (1) The urban expansion coefficient of Hefei decreases from 1.70 to 1.08 and finally tends to 1.25 from 2000 to 2015, and decreases to 0.56 from 2015 to 2020, while Nanchang fluctuates between 1.34 and 1.60 from 2000 to 2020. Hefei and Nanchang completed their industrial structure transformation in 2011 and 2018, respectively, evolving towards a trend driven by the tertiary industry. The expansion of the cities in space is inseparable from the development of social economy and the decision-making support of the government. (2) The continuous expansion of the main urban areas of Hefei and Nanchang both show a non-linear growth trend. Hefei surface heat island effect mainly expands in the northeast and southwest directions, while Nanchang mainly shows a southeast-northwest expansion pattern. Hefei and Nanchang surface heat island effect areas have increased from 45.17 km2 and 40.80 km2 to 351.61 km2 and 274.07 km2 respectively during the period, and the development intensity and scope of heat island are consistent with the scale and direction of rapid urban development. (3) The explanatory power of each influencing factor on the intensity of heat island effect in Hefei and Nanchang from large to small is: population density (0.891/0.844), built-up area (0.842/0.810), per capita GDP (0.788/0.773), proportion of secondary industry (0.679/0.711), proportion of tertiary industry (0.582/0.636), among which population density has the greatest impact, and the role of the secondary industry in the industrial structure is higher than that of the tertiary industry. In the other hand, the interaction of each factor has a greater impact on the intensity of the surface heat island effect than a single factor alone. The research results can provide a reference for the planning of Hefei, Nanchang and similar cities, and it seems that reasonable layout of green space in built-up areas and control of urban population can effectively alleviate the development speed of urban surface heat island effect.

Key words: urban surface heat island effect, surface temperature, Landsat, geographical detector