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The urban heat island (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><mi>I</mi></mrow></semantics></math></inline-formula>) refers to the land surface temperature (<i>LST</i>) difference between urban areas and their undeveloped or underdeveloped surroundings. It is a measure of the thermal influence of the urban built-up area expansion (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>B</mi><mi>A</mi><mi>E</mi></mrow></semantics></math></inline-formula>), a topic that has been extensively studied. However, the impact of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>B</mi><mi>A</mi><mi>E</mi></mrow></semantics></math></inline-formula> on the <i>LST</i> differences between urban areas and rural areas (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>R</mi></mrow></msub></mrow></semantics></math></inline-formula>) and between urban areas and emerging urban areas (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>S</mi></mrow></msub></mrow></semantics></math></inline-formula>) in different seasons has seldom been investigated. Here, the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>S</mi></mrow></msub></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>R</mi></mrow></msub></mrow></semantics></math></inline-formula> in 34 major metropolitan regions across China, and their spatiotemporal variations based on long-term space-borne observations during the period 2001–2020 were analyzed. The <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>B</mi><mi>A</mi><mi>E</mi></mrow></semantics></math></inline-formula> quantified by the difference in landscape metrics of built-up area<i>s</i> between 2020 and 2000 and their impact on <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><mi>I</mi></mrow></semantics></math></inline-formula> was further analyzed. The <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>B</mi><mi>A</mi><mi>E</mi></mrow></semantics></math></inline-formula> is impacted by the level of economic development and topography. The <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>B</mi><mi>A</mi><mi>E</mi></mrow></semantics></math></inline-formula> of cities located in more developed regions was more significant than that in less developed regions. Coastal cities experienced the most obvious <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>B</mi><mi>A</mi><mi>E</mi></mrow></semantics></math></inline-formula>, followed by plain and hilly cities. The <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>B</mi><mi>A</mi><mi>E</mi></mrow></semantics></math></inline-formula> in mountainous regions was the weakest. On an annual basis, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>R</mi></mrow></msub></mrow></semantics></math></inline-formula> was larger than <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>S</mi></mrow></msub></mrow></semantics></math></inline-formula>, decreasing more slowly with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>B</mi><mi>A</mi><mi>E</mi></mrow></semantics></math></inline-formula> than <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>S</mi></mrow></msub></mrow></semantics></math></inline-formula>. In different seasons, the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>S</mi></mrow></msub></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>R</mi></mrow></msub></mrow></semantics></math></inline-formula> were larger, more clearly varying temporally with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>B</mi><mi>A</mi><mi>E</mi></mrow></semantics></math></inline-formula> in summer than in winter, and their temporal variations were significantly correlated with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>B</mi><mi>A</mi><mi>E</mi></mrow></semantics></math></inline-formula> in summer but not in winter. The seasonal difference in <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>R</mi></mrow></msub></mrow></semantics></math></inline-formula> was larger than that of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>S</mi></mrow></msub></mrow></semantics></math></inline-formula>. Both the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>S</mi></mrow></msub></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>R</mi></mrow></msub></mrow></semantics></math></inline-formula> in coastal cities were the lowest in summer, decreasing the fastest with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>B</mi><mi>A</mi><mi>E</mi></mrow></semantics></math></inline-formula>, while those in mountain cities decreased the slowest. The change in the density of built-up lands was the primary driver affecting the temporal variations in <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>S</mi></mrow></msub></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><msub><mi>I</mi><mrow><mi>U</mi><mo>−</mo><mi>R</mi></mrow></msub></mrow></semantics></math></inline-formula> during <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>B</mi><mi>A</mi><mi>E</mi></mrow></semantics></math></inline-formula>, followed by changes in proportion and shape, while the impact of the speed of expansion was the smallest, all of which were more obvious in summer than in winter. The decreased density of built-up lands can reduce <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>U</mi><mi>H</mi><mi>I</mi></mrow></semantics></math></inline-formula>. These findings provide a new perspective for a deeper understanding of the effect of urban expansion on <i>LST</i> in different seasons.