基于长时序MODIS数据的中国城市昼夜热岛强度时空特征

随着我国城市化进程的加快,城市热岛难显缓解之势,有关土地利用/覆盖类型、城市规模、城市形态对城市热岛的影响已有较多研究,尚缺少气候背景对我国城市昼夜地表热岛强度的影响研究。本文通过长时序的MODIS地表温度数据,从年均、季节和昼夜3个时间尺度,从全国、气候带、城市3个空间尺度探讨了我国347个城市昼夜地表热岛强度的空间分布特征以及时间变化规律。结果表明：① 昼夜差异：我国城市年均地表热岛强度白天（1.25±0.81 ℃）高于夜晚（0.79±0.43 ℃）;② 季节差异：昼夜地表热岛强度在不同季节表现不同,白天表现为夏季高,冬季弱,夜晚四个季节差异不大;③ 气候带差异：昼夜地表热岛强度分布呈现明显的空间分异。白天地表热岛强度表现为热带及亚热带地区高于温带及高原地区,其中南亚热带表现为最强,高原气候区最弱;夜晚则表现为温带高于亚热带、热带及高原地区,其中中温带最强,北亚热带最弱;④ 时空变化：白天地表热岛强度年际呈非显著下降趋势（|Z|<1.96）,而夜晚呈显著上升趋势（|Z|>1.96）;昼夜地表热岛强度年际变化存在季节差异,白天地表热岛强度夏季上升趋势显著高于其他季节,夜晚四个季节都呈显著上升趋势,其中冬季地表热岛强度上升趋势最大;白天呈显著上升趋势的城市主要分布在热带及南亚热带地区,夜晚呈显著上升趋势的城市广泛分布在中温带和暖温带。

Temporal and Spatial Characteristics of Diurnal Surface Urban Heat Island Intensity in China based on Long Time Series MODIS Data

As China's urbanization process accelerates, urban heat island is difficult to alleviate. There have been many studies on the impact of land use/cover type, city size, and urban morphology on urban heat islands. There is still a lack of research on the impact of climate background on the intensity of diurnal Surface Urban Heat Islands (SUHII) in China. To explore the temporal and spatial distribution characteristics of diurnal SUHII in different climatic regions in China, this study firstly uses the GEE cloud platform to obtain the annual and seasonal average surface temperature data of each city and the area of urban and suburban, and then calculates the SUHII of each city. The Sen's slope method and M-K non-parametric trend test method are used to calculate the temporal change trend of diurnal SUHII in China. Finally, this study discussed the spatial distribution and temporal changes of SUHII from the spatial and temporal scales. The results show that: (1) Diurnal differences: the annual average SUHII of cities in China at daytime (1.25±0.81 ℃) is higher than that at nighttime (0.79±0.43 ℃); (2) Seasonal differences: the diurnal SUHII has different results in different seasons. The daytime SUHII is high in summer and weak in winter. There are little differences between the four seasons at night; (3) Differences in climatic regions: the distribution of diurnal SUHII shows obvious spatial differentiation. The daytime SUHII in the tropics and subtropics is higher than that in temperate and plateau climate regions, with the strongest SUHII occurring in the southern subtropics and the weakest SUHII occurring in plateau climate regions. The nighttime SUHII is higher in the temperate regions than in tropical, subtropical, and plateau climate regions, with the strongest occurring in the mid-temperate regions and the weakest occurring in the northern subtropics; (4) Temporal and spatial changes: The daytime SUHII shows a non-significant downward trend (|Z|<1.96), while nighttime SUHII shows a significant upward trend (|Z|>1.96). There are seasonal differences in the inter-annual variation of diurnal SUHII. In the daytime, the upward trend of SHUII in summer are significantly higher than that in other seasons, and nighttime SHUII shows a significant upward trend in all seasons, of which SUHII has the largest upward trend in winter. Cities with a significant upward trend in the daytime are mainly distributed in the tropics and southern subtropics, and cities with a significant upward trend at night are widely distributed in the mid-temperate and warm-temperate regions.