Monitoring lake-level changes in the Qinghai-Tibetan Plateau using radar altimeter data (2002-2012)

Lake-level change can be an important indicator for the water balance in the Qinghai-Tibetan Plateau (QTP). However, it is not feasible to perform continuous in-situ measurements for a large number of lakes because of the remoteness and harsh climatic conditions on this plateau. Satellite altimetry has been successfully used for monitoring water-level changes of inland lakes in recent years. In this study, water-level changes between 2002 and 2012 of 51 lakes on the QTP were monitored using multialtimeter data from Envisat/RA-2, Cryosat-2/Siral, Jason-1/Poseidon-2, and Jason-2/Poseidon-3. The water levels of 42 of the lakes have a mean rising trend of 0.275 m/a, whereas the water levels of nine lakes have a mean decreasing trend of -0.144 m/a. Overall, the water level of these lakes had a mean increasing trend of 0.201 m/a in the past 10 years. For the lakes distributed over the entire plateau, it was found that the lake levels in different basins had different change characteristics: the lake levels in the southern plateau show a decreasing trend, whereas lake levels in the northern plateau show an increasing trend. In the central plateau, the water levels of most lakes also show an increasing trend but the water levels of a small number of the lakes show a decreasing trend. In addition, the winter or summer linear trends for the levels of individual lakes appear to be opposite to the trends observed for the yearly average. The combined use of data from several different altimeters makes the temporal resolution of lake-level change measurements higher than for those results derived using only one kind of altimeter data. However, the number of lakes monitored in this study is affected by the footprints of satellites orbits on the Earth's surface. After taking into account anomalous lake levels, systematic elevation differences, and periodic changes in the water level, the biggest root-mean-square-error for the lakes monitored in this study is <40 cm/a showing that the results have a high degree of accuracy. Lake-level change is mainly related to rising temperatures, increasing precipitation, and decreasing evaporation. In particular, rising temperatures accelerate the melting of glaciers and perennial snow cover and trigger permafrost degradation, leading to an increase in the water level of most lakes across the plateau. (C) 2013 Society of Photo-Optical Instrumentation Engineers (SPIE)