基于FSDAF模型的干旱区典型绿洲城市夏季地表热岛效应时空演变研究

全球城市化进程加快引起的干旱区绿洲城市热岛效应变化及其生态环境问题已成为当前国内外城市气候、环境和生态等领域的研究热点之一。基于遥感热红外通道反演的地表温度(Land surface temperature,LST)是开展城市地表热岛(Surface urban heat island,SUHI)效应监测研究的关键参数。然而,受热红外遥感数据“时空矛盾”的制约,目前在单一星载卫星传感器下尚不存在同时具有高时间分辨率和高空间分辨率的热红外遥感数据源,因而制约了在干旱区绿洲城市范围内开展高精度地表热岛效应监测研究。针对上述问题,以干旱区典型绿洲城市--乌鲁木齐市为研究区域,以Landsat系列影像和MODIS地表温度产品为基础数据源,基于FSDAF(Flexible spatiotemporal data fusion method)时空融合模型分析了2001-2018年乌鲁木齐市在城市扩张背景下夏季地表热岛效应的时空变化特征以及夏季LST与城市地表参数之间的关系。研究结果表明:(1)乌鲁木齐市夏季热岛强度(SUHI intensity,SUHII)在不同的郊区范围内均呈现增加的趋势。在较小的郊区范围内,SUHII1从2001年的1.24℃增加到了2018年的2.83℃;在较大的郊区范围内,SUHII2从2001年的1.44℃增加到了2018年的2.88℃;(2)在研究区各土地利用类型中,裸地的夏季LST最高,水体最低;(3)研究区地表反照率和不透水面的增加与城市夏季LST升高呈正相关,而植被指数与植被覆盖度则与LST呈负相关关系;(4)在干旱区绿洲城市,城区内部植被面积的增加有助于缓解城市热岛效应,而仅郊区植被的增加则会导致SUHII的进一步增强。

Spatiotemporal variations of the summer daytime surface urban heat island of oasis city in arid area based on FSDAF model

The urban heat island effect and ecological and environmental problems of an oasis city in an arid area resulting from the acceleration of the global urbanization process have become one of the current research hotspots worldwide.As a critical parameter in investigating the surface urban heat island(SUHI),the land surface temperature(LST)retrieved from thermal infrared images is,to some extent,inaccurate because there is no single sensor that can capture real-time LST at both high spatial and temporal resolutions.This paper used the flexible spatiotemporal data fusion method to generate high spatiotemporal resolution summer daytime LST data in 2001,2011,and 2018.Spatiotemporal variations of the summer daytime SUHI over Urumqi,an oasis city in the arid area of western China,were assessed based on several urban surface biophysical variables.The results show that the SUHI intensity(SUHII)in Urumqi during the study period was calculated using two indicators of SUHII1(the urban and smaller rural area difference in the average LST)and SUHII2(the urban and larger rural area difference in the average LST).Significantly increasing trends of SUHII in the study area were observed.SUHII1 increased from 1.24℃ in 2001 to 2.36℃ in 2011 and 2.83℃ in 2018,whereas SUHII2 increased from 1.44℃ to 2.58℃ and 2.88℃ in the same periods.The highest and lowest summer daytime LST values were observed over areas of bare soil and water,respectively.The distribution of the summer daytime LST correlated positively with the albedo,the impervious surface area,and it correlated negatively with the enhanced vegetation index and fractional vegetation cover.The results emphasize the role of bare soils in aggravating the SUHI in cities in arid areas.Finally,we find that in oasis cities in arid areas,such as Urumqi,although increasing the amount of vegetation covering the urban area may be an effective way to mitigate the SUHI,more profuse vegetation coverage within a larger rural area will increase the SUHII during the summer daytime.