[Insert Figure 3 here]
3.2 Lake level variations based on SARAL and Sentinel-3
altimetry
data
In
order to examine whether abrupt water level increase during 2016-2018
occurred similarly in other Tibetan lakes, we investigated the water
level changes of a total of 12 lakes from 2013 to 2018 by combining
SARAL and Sentinel-3 altimetry data. Six of them were aimed to
inter-compare with the Hydroweb and DAHITI altimetry data. Fig. 4
presents the comparisons of water-level time series from Hydroweb/DAHITI
data archives and SARAL/Sentinel-3 data between 2013 and 2018 for
Qinghai Lake, Nam Co, Ayakkum, Migriggyangzham Co, Zhari NamCo and
Tangra YumCo. The water level time series for all the lakes indicate
that not only are the general trends derived from two data sources
comparable but the abrupt changes and intra-annual variations of lake
level are overall consistent. For example, both data sources clearly
depict a sudden increase of about 1.0 m during the wet season
(July-September) of 2017 for Zhari NamCo. The characteristics of water
levels rises in wet seasons and declines in dry seasons are also in good
agreement for all the lakes, suggesting that SARAL and Sentinel-3 data
have reliable results.
Based on the above validation, the SARAL and Sentinel-3 data were used
to monitor the lakes larger than 100 km² in the TP, and the water level
time series are shown in Fig. 5. The six lakes display an evident trend
of water level increase at varying rates during 2016-2018. For example,
the alpine lakes between the Tanggula and Kunlun Mountains, including
XijingUlan Lake, Mingjing Lake and UlanUla Lake, showed a significantly
rise (exceeding 1 m/a). In contrast, the lake level for Gyariog Co
showed an inter-annual fluctuation.