Abstract:

Ecological environment of the Lijiang River in Guilin has been degenerating quickly since the forest on its upper reaches was devastated  for the eighties of last century.Spatiotemporal variance of land surface thermal field affects forest evapotranspiration and hydrological effect directly.Therefore,vegetation coverage was retrieved with normalized vegetation index,and land surface temperature was done with Monowindow algorithm respectively from five TM/ETM+images of upper reaches of the Lijiang River during 1989 to 2006.Normalized temperature was proposed so that different temporal land surface thermal fields could be compared with each other.Effect that spatiotemporal variance of vegetation coverage affected land surface thermal field was analyzed.Results showed that land surface temperature decreased with vegetation coverage increasing.The effect became weak when vegetation coverage was very high or very low.From 1989 to 2000,the proportion of medium and high vegetation coverage area droped from 961% to 659%.It resulted in the increasing of the pixels with higher normalized surface temperatures.Although the proportion of medium and high vegetation coverage area rose to 908% from 2000 to 2006,it was still a little lower than that in 1989.It resulted in the decreasing of the pixels with higher normalized surface temperatures.Vegetation coverage could effectively reduce land surface temperature on the upper reaches of the Lijiang River