Abstract:

Understanding the spatiotemporal heterogeneity and climate zone-dependent mechanisms of urban heat island (UHI) effects is critical for developing targeted mitigation strategies under global warming and rapid urbanization. However, existing studies lack comprehensive analyses of climate-specific variations and diurnal and nocturnal interactions of UHI driving factors. Thus, this study utilized a random forest model combined with Sen's slope estimator and Mann-Kendall Test (Sen+MK) trend analysis to systematically investigate the spatiotemporal patterns and driving mechanisms of summer surface urban heat island intensity (SUHII) across 65 Chinese cities spanning temperate, cold, and arid Köppen climate zones. Using MODIS remote sensing data, meteorological observations, and socioeconomic indicators from 2003 to 2022, we revealed three key findings: 1) Spatial Patterns: The daytime and nighttime SUHII exhibited distinct differentiation across climate zones, that is, a “day decrease-night increase” reversal pattern. Specifically, SUHII decreased with increasing aridity of climate zones during the daytime (temperate zone 4.98 ℃>cold zone 4.30 ℃>arid zone 2.16 ℃) and at night (arid zone 2.92 ℃> cold zone 2.29 ℃>temperate zone 1.83 ℃). 2) Temporal Trends: A decreasing trend was observed in 54% of cities in daytime SUHII (p<0.01, with significant areas concentrated in the temperate zone), while 48% of cities exhibited a significant increase in nighttime SUHII, mainly in the southern cold and northern temperate zones. 3) Driving Mechanisms: The urban-rural white sky albedo difference (ΔWSA) emerged as the dominant universal driver, although significant climate zone-specific variations were observed. Urban greening and land-use strategies should prioritize ΔWSA mitigation through surface material optimization, green coverage expansion, and impervious surface reduction to regulate surface heat accumulation and mitigate the effects of UHI. In temperate zones, the SUHII is diurnally regulated by ΔWSA, precipitation (PRE), and elevation (DEM). Constructed wetlands and integrated water management can enhance evapotranspiration and effectively moderate temperature variations. Cold temperate zones exhibited distinct patterns: daytime SUHII responded to vegetation differences (ΔEVI), whereas nighttime intensity was driven by population density (POP). This requires targeted mitigation measures, including urban core population control, functional decentralization, and high-albedo facade retrofits. Arid zones are consistently dominated by evapotranspiration (ET) during the diurnal cycle. These findings provide a climate-zone-differentiated perspective on SUHII dynamics, enabling the development of regionally tailored urban heat mitigation strategies.

Key words: surface urban heat island (SUHII), spatiotemporal patterns, driving factors, remote sensing data, random forest, climate zones

摘要：

在全球变暖与快速城市化协同作用下，揭示城市热岛效应（UHI）的时空异质性及其气候带依赖性机制对准确制定缓解策略至关重要。然而，当前研究对UHI驱动因子的气候带特异性及昼夜耦合效应仍缺乏系统性认识。基于2003-2022年MODIS遥感数据、气象观测及社会经济数据，运用随机森林模型与Sen+MK检验趋势分析，系统评估柯本气候分类下暖温带、冷温带和干带的中国65个城市夏季地表城市热岛强度（SUHII）时空分异规律及驱动机制。研究发现，1）空间格局：昼夜SUHII呈现显著气候带分异，呈“昼降夜升”梯度反转规律，即昼间SUHII随气候区干旱性增强递减（暖温带4.98 ℃>冷温带4.30 ℃>干带2.16 ℃），夜间呈反向分布（干带2.92 ℃>冷温带2.29 ℃>暖温带1.83 ℃）。2）时间演变：54%的城市昼间SUHII呈下降趋势（显著区域集中于暖温带），而48%的城市夜间SUHII显著上升的区域主要位于冷温带南部和暖温带北部。3）驱动机制：城乡白空反照率差异（ΔWSA）为全域主导因子，但气候带分异显著——暖温带昼夜受ΔWSA、降水（PRE）与高程（DEM）共同调控，冷温带昼间响应植被差异（ΔEVI）而夜间受人口（POP）驱动，干带昼夜均以蒸散发（ET）为主导。研究从气候带视角揭示中国SHUII昼夜分异的梯度规律与驱动机制异质性，为制定气候带适配的热岛缓解方案提供科学依据。

关键词: 城市热岛效应, 时空特征, 驱动因子, 遥感数据, 随机森林, 气候带