Abstract:

From the middle Jan.to the beginning of Feb.in 2008，an extreme weather and climate event with continuous low temperature，snow and sleet had occurred in the middle and lower reaches of the Yangtze River.The event had caused heavy snow disaster.Taking Hubei Province as an example，the snow disaster is dynamically monitored and evaluated based on RS and GIS.Using many days of successive satellite data from EOS/MODIS and observation data of snow depth from Hubei weather stations，the normalized difference snow index (NDSI) was calculated，and then the snow distribution information was obtained with the support of geographical information system.According to different height above sea level，the thresholds of NDSI related to the snow depth at different levels were determined，and then the recognition of three levels snow depth (0~10，10~20 and 20~30 cm) was implemented.Snow areas of different depth in the different land use type were respectively counted according to different land use classification data and snow distribution data.Dynamic monitoring result of the heavy snow disaster process expressly shows that about 90% land areas in Hubei Province were covered by heavy snow，the snow disasters in Jianghan plain，northeast and southeast Hubei were the worst，snow depth in parts of region in Hubei Province was above 20 cm；heavy snow worst affects farm land such as paddy field，dry land and water body such as lake，reservoir，ditch；biggish range in residential areas was also hit by snow；since Feb.2，2008，the area of heavy snow had gradually reduced；after Feb.8，2008，heavy snow almost thawed.Based on the study above，the operation flow of heavy snow monitoring in the middle and lower reaches of the Yangtze River with the support of remote sensing and geographical information system has been formed.

Key words: snow disaster/RS and GIS/NDSI；snow depth/land use