TWELVE YEAR OF WATER RESOURCE MONITORING OVER THE YANGTZE MIDDLE REACHES EXPLOITING DRAGON TIME SERIES AND FIELD MEASUREMENTS

摘要

Within the framework of the DRAGON program, a relative long term surveillance, 12 years, of the Poyang and Dongting lakes, considered as key elements of the Yangtze watershed in terms of water resource, flood redaction and for biodiversity maintain has been realized. This was done combing altimetry, in situ measurements, SAR and optical MR and HR time series with a high revisiting frequency of 10 days. A first major output corresponds, particularly within the context of lost of Envisat and Sentinels’ data availability expected in 2014,corresponds to the potential’sanalysis of a large range of MR and HR optical and SAR data for water bodies monitoring in term of quality, potential and accuracy. Over the years, changes in the type of data used are very indicative of a share of the resource available, and also of technological improvement over the years. It can be noticed since 2008, that, the part of HR optical data, Beijing1, DEIMOS, HJ1 A-B has increased significantly. In regards to the two years gap in term of data resource before the availability of the first Sentinel data, some recommendations can be given to insure the monitoring of large water bodies. Thematically specking, major outputs is the characterization of the important inter annual, and intra annual variations in term of water height and water extent of both lakes, variations that are linked with rainfall variations at sub basins and Yangtze basin scales. This 12 years period is marked by general non linear tendencies of water resources decreasing even if two major flood events occurred in 2002 and 2010. Drought tendency and drought intensity has been precised. During winter 2011-2012, EO data analysis allowed given the real size of the water surface extent as 720 km2 when Medias were speaking about 200 km2; the driest winter for the latest decade being the 2003-2004 as shown by the time series comparison. These analysis also highlight the very fast change from extreme stage to another as in June 2010 as when the transition from drought to an extreme flood stages occurred in less than 3 weeks. In addition to the water height/surface monitoring, for water resource analysis, same data set were exploited for modelling constraints (ie Donting lake modeling, with CSK, HJ1A/B and ENVSIAT ASAR) and also for water quality motoring (HJ1A/B, Deimos), for the mapping of vegetation units groups (SPOT, Beijing1, ALOS) and vegetation growth have been carried. Downstream exploitations of these keys elements characterizing inland ecosystem will be presented, epidemiology (Schistosiomaisis over Poyang and Dongting lakes based on intermediate host ecosystem monitoring) and biodiversity (Human practices and birds location ...). Finally, the obtain results allow to have a good idea of the ways of exploiting the future Sentinels that will be a powerful tool for mapping and monitoring rich complex and sensitive large ecosystems such as the monsoon lakes in China and Asia, but also at a global scale, all large coastal or inland delta all around the worldThis synergistic exploitation of data derived from Earth observation systems and in situ data will provide very valuable information for the water resource management at the scale of the middle Yangtze watershed.