Water surface variations monitoring and flood hazard analysis in Dongting Lake area using long-term Terra/MODIS data time series

Dongting Lake is the second largest freshwater lake in China, and its water surface area varied very significantly during last decade. Remote sensing technology has more advantages in macro monitoring of lake water surface area than the traditional methods. In the paper, an integrated threshold method of water body extraction based on MODIS data is given, which synthesizes several factors, including vegetation index-NDVI, spectrum characters of water body, cloud and shadow, and the SRTM digital elevation information. With this method and 356 scenes MODIS 8-Day composite (MOD09Q1) image, water surface area of Dongting Lake was dynamically monitored from 2000 to 2009. The result shows that during 1 year, the water area variation in Dongting Lake area had a typical seasonal (monsoon) behavior, and during last decade, the water area decreased gradually and obviously. Based on variation monitoring, yearly max-submersion time index has been suggested to analyze flood hazard in study area. With the support of ArcGIS software, authors estimated the yearly submersion time of the Dongting Lake for each year separately and average submersion time from 2000 to 2009. The result shows 67.46% of study area is being with high flood hazard.