Poyang and Dongting Lakes, major water resources and key elements for natural flood control and reduction within the Yangtze River middle basin, were monitored from 2000 to 2008, with a re-visiting period of 10 days, using ENVISAT ASAR, and completed by MODIS data, validated by Beijing 1 time series. GPCP and TRMM time series were utilized to derive regional meteorological indicators. At the lake scale as well as their subdivisions ones, results allowed the characterization of lake behaviors. Even if the Dongting and Poyang lakes mechanisms are substantially different, their water surface areas and water level variations exhibit a good similarity, including the same year of major flooding (2002) and the same year of lowest extent of inundation (2001). Both lakes present astonishingly low water levels and low surface areas in summer of 2006, being associated with a very early draw-off. Few reasons could explained it: (i) a rainfall deficit at the sub-watershed level; (ii) a hydrological event in the upper stream part, namely a possible closure of the Three Gorges Dam (TGD) gates; or (iii) a global climate change effect at the regional scale. The reasons for the dramatic water dropdown are neither a local rain deficit nor a change in the TGD management. The smallest water extent for wet season observed in 2006, appeared to be linked with a severe drought within the upper stream part of the Yangtze River basin. In addition, an impressive decreasing tendency of water surface and level is observed in the middle reaches of the Yangtze River, linked with relatively constant decreasing precipitations over the last decade. This synergistic utilization of data from earth observation systems and in situ data provide valuable information on water resource management at the scale of the middle Yangtze River watershed.

No abstract

No abstract

Poyang Lake, one of the most regularly flooded areas in China, can be considered as a key natural flood control and reduction element within the Changjiang middle basin. Within the Flood DRAGON Project, part of the MOST-ESA DRAGON Programme, Poyang Lake's water extent was monitored based on 64 ENVISAT low and medium resolution ASAR and MERIS Full Resolution data, over a two and half year period. It's the first time that such an amount of ENVISAT data was exploited in monitoring inland lake water extent variations. This original integration approach permitted: lake-surface variation analysis, yearly submersion-time estimation, and the recognition of three hydrological sub-systems. The results highlight the great potential of ENVISAT and more largely of Earth Observation Medium Resolution data in monitoring and managing large inland water bodies. This approach can be applied worldwide in a global climate change context.

No abstract