剖析百年尺度的城市变迁与气候要素变化对提升区域气候演变机理的认知具有重要意义.本文基于卫星遥感图像、社会经济数据和气象站点实测等数据,采用人机交互解译方法,刻画了 1916-2020年北京城市扩展过程.利用滑动平均法和Mann-Kendall趋势检验方法,分析了关键气象要素的变化特征,从而揭示了百年尺度城市土地利用变化和社会经济发展与区域气候变化之间的关系.研究表明:1916-2020年北京城市土地面积增长了64.48倍,围绕中心地域呈圈层式蔓延扩展,呈现"缓慢—加速—减速"的扩展模式,城市扩展速度在2000-2010年达到峰值,为70.12 km2/a.1916-2020年北京的5 a滑动平均气温和年降水量分别为12.25℃和588.6 mm.随着城市发展,1916-2020年北京市5 a滑动平均气温以0.22℃/10a波动上升,1978年以来升温显著.年降水量则呈现波动下降趋势,速率为9.37 mm/10a.城市不透水面的加速扩张可能造成地表能量收支的改变,从而引发城市变暖.城市化率与气温升高具有协同关系,不同时段差异显著,1916-2020年北京城市化对区域升温的贡献为20.83％.另一方面,地表能量收支改变与空气污染物排放增加可能导致北京城市地区降水减少.本文结果可为提升北京城市变迁对区域气候演变影响过程和机制的认知提供科学参考.

持续地开展国家尺度土地利用/覆盖变化遥感监测对于新时代国土空间规划和"美丽中国"蓝图绘制具有重要的科学价值.本文采用Landsat 8 OLI、GF-2等卫星遥感数据,融合遥感大数据云计算和专家知识辅助人机交互解译方法,研发了中国土地利用变化(2015-2020年)和2020年土地利用现状矢量数据(CLUD 2020),建立了完整的30 a(20世纪80年代末—2020年)每隔5 a的30m分辨率中国土地利用动态数据库.基于CLUD 2020数据,从全国和区域两个尺度揭示了2015-2020年中国土地利用变化的总体规律、区域分异和主要特征.研究表明:将遥感大数据云计算生成的30 m分辨率植被覆盖变化和地表类型变化检测信息融入到人机交互遥感解译方法,可有效地提高大范围土地利用变化遥感制图的效率和变化图斑辨识的准确性;精度评价表明,CLUD 2020一级类型制图的综合精度达95％.总体上,全国范围内国土空间开发强度与2010-2015年比较进入相对稳定状态.期间全国耕地面积仍保持减少态势,空间分异特征为耕地南减北增,东北松嫩平原及其与三江平原交界区大规模的旱地向水田转移,西北新疆南部开垦和北部退耕/撂荒并存;全国城乡建设用地持续增加,空间分异特征表现为由以往的沿海地区和超大、大城市集聚转向中西部地区的大中小城镇周边蔓延为主.全国范围的林草自然生态用地面积持续减少,但强度与2010-2015年比较有所下降;受气候变化的持续影响,青藏高原地区的河流湖泊等水域面积显著增加.以上土地利用变化格局与"十三五"期间国家高质量发展、生态文明建设宏观战略和气候变化的影响密切相关.

Accurate measurements of the three-dimensional structure characteristics of urban buildings and their greenhouse effect are important for evaluating the impact of urbanization on the radiation energy budget and research on the urban heat island (UHI) effect. The decrease in evapotranspiration or the increase in sensible heat caused by urbanization is considered to be the main cause of the UHI effect, but little is known about the influence of the main factor “net radiant flux” of the urban surface heat balance. In this study, experimental observation and quantitative model simulation were used to find that with the increase of building surface area after urbanization, the direct solar radiation flux and net radiation flux on building surface areas changed significantly. In order to accurately quantify the relationship between the positive and negative effects, this study puts forward the equivalent calculation principle of “aggregation element”, which is composed of a building’s sunny face and its shadow face, and the algorithm of the contribution of the area to thermal effect. This research clarifies the greenhouse effect of a building with walls of glass windows. Research shows that when the difference between absorption rates of a concrete wall and grass is −0.21, the cooling effect is shown. In the case of concrete walls with glass windows, the difference between absorption rates of a building wall and grass is −0.11, which is also a cooling effect. The greenhouse effect value of a building with glass windows reduces the cooling effect value to 56% of the effect of a building with concrete walls. The simulation of changes in net radiant flux and flux density shows that the greenhouse effect of a 5-story building with windows yields 15.5% less cooling effect than one with concrete walls, and a 30-story building with windows reduces the cooling effect by 23.0%. The simulation results confirmed that the difference in the equivalent absorption rate of the aggregation element is the “director” of cooling and heating effects, and the area of the aggregation element is the “amplifier” of cooling and heating effects. At the same time, the simulation results prove the greenhouse effect of glass windows, which significantly reduces the cold effect of concrete wall buildings. The model reveals the real contribution of optimized urban design to mitigating UHI and building a comfortable environment where there is no atmospheric circulation.

: Human land use intensity a ff ects the surface energy balance by changing the biogeophysical parameters. This study used Moderate Resolution Imaging Spectroradiometer remote sensing data and surface energy balance algorithms to quantify changes in surface energy budgets corresponding to changes in land use in Beijing from 2000 to 2015. Land use was reclassified by considering land use intensity. The di ff erence in the latent heat flux (LE) and net radiation (R n ) (LE − R n ) expressed the warming or cooling e ff ect. The results showed that: (i) The increasing trend of net longwave radiation in Beijing o ff set the decreasing trend of net shortwave radiation. The R n changed slightly, while the LE and LE − R n showed a significant increase of 0.55 and 0.56 W / (m 2 · year), respectively. The findings indicated that considering only radiative forcing, or even R n , was not enough to measure the impacts of land use change on the energy budget. (ii) The order of R n , LE, and LE − R n values from high to low were natural and seminatural areas, cropland, mixed pixel areas, urban expansion areas, and old urban areas. Compared with natural and seminatural areas, the changing LE − R n trend in the other four land use types decreased with the increase in human impact intensity, indicating that human activities weakened the positive change trend of LE − R n and increased the warming e ff ect. (iii) Although the temporal trend of LE increased in Beijing from 2000 to 2015, the e ff ect of R n on LE − R n was greater than that of LE, especially in the four land use types a ff ected by human activities. The results for surface temperature in various land use types confirmed this point. This study highlights the energy budget di ff erences of various land use types a ff ected by human activities. It makes an important contribution to understanding the urban heat island e ff ect from a biogeophysical perspective.

The authors would like to change the authors’ affiliation in the recent published paper [...]

Cropland redistribution to marginal land has been reported worldwide; however, the resulting impacts on environmental sustainability have not been investigated sufficiently. Here we investigated the environmental impacts of cropland redistribution in China. As a result of urbanization-induced loss of high-quality croplands in south China (∼8.5 t ha-1), croplands expanded to marginal lands in northeast (∼4.5 t ha-1) and northwest China (∼2.9 t ha-1) during 1990-2015 to pursue food security. However, the reclamation in these low-yield and ecologically vulnerable zones considerably undermined local environmental sustainability, for example increasing wind erosion (+3.47%), irrigation water consumption (+34.42%), fertilizer use (+20.02%) and decreasing natural habitats (-3.11%). Forecasts show that further reclamation in marginal lands per current policies would exacerbate environmental costs by 2050. The future cropland security risk will be remarkably intensified because of the conflict between food production and environmental sustainability. Our research suggests that globally emerging reclamation of marginal lands should be restricted and crop yield boost should be encouraged for both food security and environmental benefits.

城市建筑立体结构特征和楼房温室效应的精准量测是评估城市化对辐射能量收支影响以及城市热岛效应研究的重要内容之一.城市化导致蒸散发减少或显热增加被认为是形成城市热岛效应的主因,而目前对于城市下垫面热量平衡主因子"净辐射通量"的影响了解甚少.文章应用实验观测和定量模型模拟,发现随着城市化后楼房表面积增加,楼房建筑表面积上太阳直接辐射通量和净辐射通量发生了明显的变化.为了准确地计算这种正负效应的定量关系,本研究提出了楼房朝阳面与其阴影面构成一体的"聚合元"等价计算原理以及面积对热效应贡献的算法,阐明了楼房玻璃窗墙壁的温室效应.研究表明,当水泥墙与草地的吸收率差值为-0.21时,体现了冷效应.在嵌有玻璃窗的水泥墙壁另一情形下,楼房墙与草地的等效吸收率差值为-0.11,也为冷效应,玻璃窗楼房的温室效应值相当于减缓到56％的水泥墙楼房冷效应值.对于净辐射通量和通量密度变化的模拟表明:5层楼温室效应相当于减少水泥墙冷效应15.5％,30层楼温室效应相当于减少水泥墙冷效应23.0％.模拟结果证实了聚合面的等效吸收率差值为冷热效应的"定向器",聚合元面积为冷热效应的"放大器".同时,模拟结果证实了玻璃窗的温室效应,明显减缓了水泥墙壁楼房的冷效应.模型能揭示在没有大气环流影响下城市的设计对减缓城市热岛现象和构建舒适环境的真实贡献.

Urban impervious surfaces area (ISA) and green space (GS), two primary components of urban environment, are pivotal in detecting urban environmental quality and addressing global environmental change issues. However, the current global mapping of ISA and GS is not effective enough to accurately delineate in urban areas due to the mosaicked and complex structure. To address the issue, the hierarchical architecture principle and subpixel metric method were applied to map 30 m global urban ISA and GS fractions for the years 2015 and circa 2020. We use random forest algorithms for retrieval of the Normalized Settlement Density Index and Normalized Green Space Index from Landsat images using Google Earth Engine. The correlation coefficients of global urban ISA and GS fractions were all higher than 0.9 for 2015 and circa 2020. Our results show global urban ISA and GS areas in circa 2020 were 31.19 × 104 km2 and 17.16 × 104 km2, respectively. The novel ISA and GS fractions product can show potential applications in assessing the effects of urbanization on climate, ecology, and urban sustainability.

Human land use intensity affects the surface energy balance by changing the biogeophysical parameters. This study used Moderate Resolution Imaging Spectroradiometer remote sensing data and surface energy balance algorithms to quantify changes in surface energy budgets corresponding to changes in land use in Beijing from 2000 to 2015. Land use was reclassified by considering land use intensity. The difference in the latent heat flux (LE) and net radiation (Rn) (LE−Rn) expressed the warming or cooling effect. The results showed that: (i) The increasing trend of net longwave radiation in Beijing offset the decreasing trend of net shortwave radiation. The Rn changed slightly, while the LE and LE−Rn showed a significant increase of 0.55 and 0.56 W/(m²∙year), respectively. The findings indicated that considering only radiative forcing, or even Rn, was not enough to measure the impacts of land use change on the energy budget. (ii) The order of Rn, LE, and LE−Rn values from high to low were natural and seminatural areas, cropland, mixed pixel areas, urban expansion areas, and old urban areas. Compared with natural and seminatural areas, the changing LE−Rn trend in the other four land use types decreased with the increase in human impact intensity, indicating that human activities weakened the positive change trend of LE−Rn and increased the warming effect. (iii) Although the temporal trend of LE increased in Beijing from 2000 to 2015, the effect of Rn on LE−Rn was greater than that of LE, especially in the four land use types affected by human activities. The results for surface temperature in various land use types confirmed this point. This study highlights the energy budget differences of various land use types affected by human activities. It makes an important contribution to understanding the urban heat island effect from a biogeophysical perspective.