资源简介

摘要： 当前很多研究关注城市扩展及其热岛效应，但不同土地利用强度对辐射能量的影响尚有待进一步的分析。以北京市为例，基于2000和2015年的土地利用数据，按照人为活动对土地的利用程度，将北京市的土地利用变化划分为5类：即老城区、城市扩展区、混合变化区、耕地及自然纯像元区。在此基础上，在反照率和太阳辐射遥感反演数据的支持下，分析2000~2015年由地表反照率引起的辐射强迫(RF, Radiative Forcing)，并探讨了RF与植被的关系。结果表明：相比自然纯像元区域，老城区、城市扩展区、混合变化区及耕地的RF在研究时段内均明显增加，后三年的RF均值比前三年增加了0.78 W/m2以上，远大于自然纯像元区的RF增量(0.19 W/m2)。本研究同时发现，植被绿度随土地利用强度的增加而逐年下降，但植被生长期长度却有所延长，两者综合作用于地表反照率，促使了RF的增加，说明单纯从辐射平衡来讲，北京市的土地利用变化在一定程度上增强了RF。 关键词： 土地覆盖;  辐射平衡;  植被指数;  物候;  反照率     Abstract: Many current studies focus on urban expansion and its heat island effect, but the impact of different land use intensity on radiant energy needs further analysis. Based on the land use data of 2000 and 2015 in Beijing, this study divided the land use of Beijing into five types according to the influence degree of human activities and vegetation resilience, namely, the old urban areas, urban expansion areas, unchanged cropland areas, mixed pixel areas with changed gridcells, and unchanged pure pixel areas. On this basis, we calculated Radiative Forcing (RF) due to the change of surface albedo and explored the relationship between RF and vegetation cover. The results showed that: (1) In pure pixel areas, natural vegetation had a lower albedo, and the corresponding RF was larger than the other four land use type areas. However, under the influence of human activities, RF in the four land use type areas showed an obvious increasing trend during the research period, and the increment was also larger than RF in PP areas. (2) Comparing with unchanged pure pixel, the EVI within the other four human-affected land type areas (old urban areas, urban expansion areas, mixed pixel, and unchanged cropland) decreased but the LOS extended. The combined effect of LOS and EVI contributed to the decreasing trend of surface albedo, which prompted the increase of RF. Our finding highlights that human activities often enhances RF by affecting the intensity of land use. This study has important reference value for analyzing the climate feedback of land use change from physical mechanism.

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