Lakes’ state and abundance across the Tibetan Plateau
Thursday, 18 December 2014
Understanding the changes in number and areal extent of lakes, as well as their abundance and size distribution is important for assessments of regional and global water resources, biogeochemical cycles and changes in climate. In this study, changes in lake area greater than 1 km2 are mapped using Landsat datasets, spanning the 1970s, 1990, 2000, and 2010. In addition, high-resolution images (GeoCover Landsat mosaic 2000, with a pixel size of 14.25 m) are used for the first time to map lakes as small as 0.001 km2 across the entire Tibetan Plateau (TP). Results show that the numbers and areal extent of individual lakes >1 km2 in size show a slight decrease between the 1970s and 1990, followed by a clear increase from 1990 to 2010. Ninety-nine new lakes are identified between the 1970s and 2010, 71 of which are found between 1990 and 2010. This indicates the accelerated glacier melt and/or increased difference of precipitation minus evaporation since the 1990s. More than 80% of the lakes show an increase in their area between the 1970s and 2010. The lake census, using 2000 imagery, shows that there are 32,843 lakes with a total area of 43,151.08 ± 411.49 km2, which makes up 1.4% of the total area of the TP. Around 96% of all lakes are small, with an area < 1 km2, while the 1,204 large lakes (> 1 km2) account for 96% of the total lake area. The TP is subdivided into 12 greater drainage basins, and of these the Inner TP dominates in terms of the number of lakes (55.03%), the total area of lakes (66%) and lake density (0.026/km2 compared to the mean, 0.011/km2). A plot of lake abundance against size shows that the size distribution of lakes departs from a typical power law distribution, but displays such a distribution at the mean elevation (4,715 m), with an r2 value of 0.97 and a slope of −0.66. The slopes of the abundance-size equations from each of the 12 greater basins, and from all basins together, are larger than −1, supporting the inference that larger lakes, rather than the small lakes, contribute more to the total lake surface area across the TP. The lake inventory provided in this study, along with the assessment of lake size distribution, have important implications for estimates of water balance, for water resource management, and for lake area estimations in the TP.