Modeling and analysis of lake water storage changes on the Tibetan Plateau using multi-mission satellite data

Estimation of the water storage changes in the lakes of the Tibetan Plateau (TP) is essential for an accurate evaluation of climate change in this alpine region and its impact on the surrounding hydrologic environment. Because of the remoteness and poor accessibility of these alpine lakes, and a lack of lake bathymetric data, estimating their mass budget over the TP poses a considerable challenge. However, the integration of optical remote sensing images, satellite altimetry data, and gravimetry data makes it possible to monitor the overall variations in lake water storage in this extensive region. The ICESat/GLAS altimetry data used in this study reveal that most of the lakes in the TP showed a significant upward tendency (0.2–0.6 m/year) in water level between 2003 and 2009, particularly those lakes that are supplied with a large proportion of glacial meltwater. A series of lake area data derived from Landsat MSS/TM/ETM + imagery over the past four decades indicate that during the 1970–1990 period most of the lakes experienced severe shrinkage, with only some of those in central and western Tibet undergoing expansion. During the 1990–2011 period, in contrast, the majority of the lakes on the TP displayed a remarkably expansion tendency. The total lake area increased from 35,638.11 km2 in the early 1970s to 41,938.66 km2 in 2011. Based on the statistical relationships between the extent of the lake surface area and lake water levels from 2003 to 2009, an empirical model for each of the region's 30 lakes is established to estimate the lake water level from the corresponding area data, thereby reconstructing time series of lake level data for each lake from the 1970s to 2011. Based on time series of lake area and water level data, a time series of lake water volume is also reconstructed. The results show that total lake water storage increased by 92.43 km3 between the early 1970s and 2011, with lakes with an area larger than 100 km2 accounting for 77.21% of the total lake water volume budget. Moreover, the GRACE signals confirm a similar spatial pattern in water mass changes, i.e., a significantly positive water mass balance in the north and center of the TP and mass loss in southeastern Tibet and along the Himalayas. The water mass budget (6.81 km3/year) derived from satellite gravimetry signals in the Chiangtang Plateau are in good agreement with the estimated rising rate of 6.79 km3/year of lake water storage in this region based on the empirical model developed in this study. The mechanism of lake water storage changes is discussed and analyzed with reference to previous studies.