Sustained growth of high mountain lakes in the headwaters of the Syr Darya River, Central Asia

The continuous rise in summer temperature and consequent glacier wastage have led to a significant loss of frozen water resources in the mountain headwaters of the major river systems in Central Asia. High mountain lakes in the headwaters of the Syr Darya River serve as sensitive indicators of climate change in the region. In this study, lakes in the headwaters of the Syr Darya River are examined using a Landsat image series. A total of 959 lakes covering a total area of 328.39 +/- 5.51 km(2) were identified in 2015, of which 91% were distributed in the larger Naryn River basin, and the remaining lakes were in the smaller Kara Darya River basin. During the period of the 1990s to 2015, a clear expansion trend in both lake area (+ 6.64 km(2)) and number of lakes (+ 205) was observed. Glacial lakes contributed 69% of the increase in the number of lakes. Among the four lake types, proglacial lakes showed the fastest area expansion with an average relative growth rate of 94% from the 1990s to 2015, 5-8 times that of the other three lake types: nonglacial lakes, unconnected-fed lakes and unconnected-nonfed lakes. Lake Petrov was the fastest growing glacial lake (+ 0.05 km(2) yr(-1)) during the past century and will continue to expand as its supply glacier continues to retreat. The continuous expansion and potential outburst risk of the Lake Petrov poses a serious threat to downstream toxic tailing ponds of the Kumtor Gold Mine. Lake Song Kol, the largest natural lake in this region, presented a steady status during 1972-2017. The warming climate-caused acceleration of glacial melt is thought to be the primary reason for the lake enlargements in this region. The lake inventory prepared here is valuable baseline dataset for the evaluation of water resources in the Syr Darya River drainage basin and for the potential risk and hazard assessments of glacial lake outburst floods.