喀斯特城市植被覆盖度时空变化对地表温度的影响

Influence of Spatio-temporal Change of Vegetation Coverage on Land Surface Temperature in Karst City

随着桂林喀斯特城市的快速扩展、地表植被覆盖度的变化,城市热岛现象越来越明显。以桂林1989-2006年5景TM/ETM遥感图像为数据源,利用遥感归一化植被指数反演植被覆盖度Pv,利用Qin单窗算法反演地表温度ts,分析Pv空间和时间变化对ts的影响。结果表明,在空间上ts随Pv的提高而降低,呈明显负相关关系。在时间上Pv<0.2面积比例逐年增加,1989年7.8%、1991年15.2%、2000年20.7%、2005年21.1%、2006年22.7%;而Pv≥0.7面积比例逐年减少,1989年49.2%、1991年27.4%、2000年27%、2005年16.5%、2006年11.1%。其导致地表温度高于茂密林地表面温度的比率z>20%的高温像元比例逐年上升;而z≤10%的低温像元比例逐年下降,1989年28.9%、1991年25.4%、2000年23.7%、2005年22.2%、2006年20.4%。植被覆盖的喀斯特山峰呈现显著的凉岛现象,从而调节喀斯特城市气候环境。

Stronger and stronger urban heat island effect could be felt with karst Guilin City rapid expansion and vegetation coverage variance.Thus,vegetation coverage Pv was retrieved with NDVI,land surface temperature（LST） was got by Qin Mono-window algorithm respectively from five TM/ETM images of Guilin during 1989 to 2006.Influence of Pv spatio-temporal variance on LST was analyzed.Results show that LST possesses a negative correlation with Pv in space as it reduces with the enhancement of Pv.While the area proportion of Pv0.2 increases,which is 7.8% in 1989,15.2% in 1991,20.7% in 2000,21.1% in 2005 and 22.7% in 2006,the area proportion of Pv≤0.7 decreases,which is 49.2% in 1989,27.4% in 1991,27% in 2000,16.5% in 2005 and 11.1% in 2006 over the period.It results in rapid rising of high LST pixel proportion of z20% and rapid falling of low LST pixel proportion of z≤10% by year,which is 28.9% in 1989,25.4% in 1991,23.7% in 2000,22.2% in 2005 and 20.4% in 2006.The vegetated karst hills show strong urban cool island effect and can improve urban microclimate environment in the karst cities.