Nine years of water resources monitoring over the middle reaches of the Yangtze River, with ENVISAT, MODIS, Beijing‐1 time series, Altimetric data and field measurements

Abstract

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.

Analyzing the Inundation Pattern of the Poyang Lake Floodplain by Passive Microwave Data

“…1) is calculated from 2001 to 2003 and compared with the Poyang Lake area from MODIS (with a spatial resolution of 250 m) and ASAR (with a spatial resolution of 30 m) data (Yésou et al 2011(Yésou et al , 2013, as shown in Table 2 (Yésou et al 2011). The trend of our retrieved WSS and standing water area is close to the Poyang Lake area, as shown in Fig.…”

“…10. In the wet case of 4 July Yésou et al (2011) and WSS and standing water area calculated from SSM/I 37 GHz.…”

“…Yésou et al (2011) focus on the Poyang Lake area, while our study area is 6250 km 2 and covers not only Poyang Lake, but also the wetland and cropland adjacent to Poyang Lake.…”

Hydroclimatological influences on recently increased droughts in China's largest freshwater lake

“…Poyang Lake is China's largest freshwater lake, which has been undergoing hydrological alterations in recent decades (Jiao, 2009;Finlayson et al, 2010;Hervé et al, 2011;Liu et al, 2013;Zhang et al, 2014). The lake is located at the south bank of the Yangtze River, which is a humid monsoon climatic region.…”

“…Since Poyang Lake receives inflows from its surrounding basin and discharges into the Yangtze River via a narrow outlet at the Hukou (Fig. 1), the strong lake-river interaction makes it complex to separate relative impacts of the inflow and outflow on the lake stage (Hu et al, 2007;Lai et al, 2014a). Zhang et al (2014) employed a hydrodynamic model for Poyang Lake for the separation and declared that the lake decline in the 2000s was primarily ascribed to the weakened blocking effect of the Yangtze River.…”