Alpine lakes on the Tibetan Plateau are minimally disturbed by human activities and are sensitive indicators of climate variability. Accelerated lake expansion in the 2000s has been confirmed by both dramatic lake‐area increases (for 312 lakes larger than 10 km²) derived from optical images, and rapid water‐level rises (for 117 lakes with water‐level data) measured by satellite altimetry. However, the underlying climate causes remain unclear. This paper analyzes the relationship between the water‐level changes of lakes on the plateau and the potential driving factors, such as the glacier meltwater supply and a dependency on precipitation and runoff over the whole plateau and in each zone. The results show that the rates of change of non‐glacier‐fed lakes in the 2000s were as high as those of glacier‐fed lakes across the whole plateau and the lake‐level changes were closely associated with the lake supply coefficients (the basin/lake area ratio). The lake variations agreed well with the spatial pattern of precipitation changes. However, in different zones, especially at around 33°N north of the plateau, glacier‐fed lakes did exhibit faster lake level increases than no‐glacier‐fed lakes, indicating that the presence of a glacier meltwater supply augmented the precipitation‐driven lake expansions in these areas. Despite the absence of quantitative modeling due to limited data availability, this study provides qualitative support that the lake expansions on the Tibetan Plateau in the 2000s have been driven primarily by changes in precipitation and evapotranspiration and not solely by the effect of glacier wastage.

The Tibetan Plateau is an essential source of water for Southeast Asia. The runoff from its ~34 000 glaciers, which occupy an area of ~50 000 km², feeds Tibetan lakes and major Asian rivers like the Indus and Brahmaputra. Reported glacial shrinkage likely has an impact on the runoff. Unfortunately, accurate quantification of glacial changes is difficult over the high-relief Tibetan Plateau. However, it has recently been shown that it is possible to directly assess water level changes of a significant number of the ~900 Tibetan lakes with an area over 1 km². This paper exploits different remote sensing products to create drainage links between Tibetan glaciers, lakes and rivers. The results allow us to differentiate between lakes with and without outlet. In addition, we introduce the notion of geometric dependency of a lake on glacial runoff, defined as the ratio between the total area of glaciers draining into a lake and the total area of the lake catchment. We determined these dependencies for all ~900 sufficiently large Tibetan lakes. To do so, we combined three remote sensing products: the CAREERI glacier mask product, a lake mask product based on the MODIS MOD44W water product and the HydroSHEDS river network product derived from Shuttle Radar Topography Mission (SRTM) elevation data. Using a drainage network analysis, we determined all drainage links between glaciers and lakes. The results show that 25.3% of the total glacier area directly drains into one of 244 Tibetan lakes. The results also give the geometric dependency of each lake on glacial runoff. For example, there are ten lakes with direct glacial runoff from at least 240 km² of glacier. Three case studies, including one of the well-studied Nam Tso Lake, demonstrate how the geometric dependency of a lake on glacial runoff can be directly linked to hydrological processes.

The Tibetan plateau is covered by hundreds of larger and smaller lakes. Until recently there was no method to monitor their water level variations due to lack of in-situ measurements or unfitness of available remote sensing methods. However the ICESat/GLA14 laser altimetry data provide global surface elevations for land during 18 one-month campaigns between 2003 and 2009. This product could be used to accurately monitor water level variations and to estimate annual water level trends of about 150 Tibetan lakes. Based on the ICESat campaign schedule, lake levels derived from the GLA14 data are classified into three groups referenced to the Tibetan seasons: late dry, early wet, and early dry. For each lake sampled by sufficient ICESat campaigns, seasonal water level trends could be estimated and inter-seasonal lake level variations could be determined. The results indicate that most of the southern Tibetan lakes have a downward seasonal trend while most lakes elsewhere in Tibet have a positive seasonal trend. This means that these seasonal trends are similar to the annual trends. Moreover, lake level variations between seasons are much larger in the south than in the north and the west of Tibet. Based on the spatial pattern of the lakes, the Tibetan plateau is divided into four sub-areas corresponding to seasonal lake level trends and inter-seasonal lake level variations. The results confirm climatic trends as discussed in meteorological literature. Therefore, this analysis is expected to improve the understanding of the limnological processes on the Tibetan plateau and their impacts on the surrounding regions.

Monitoring glacier changes is essential for estimating the water mass balance of the Tibetan Plateau. In this study, we exploit ICESat laser altimetry data in combination with the SRTM DEM and the GLIMS glacier mask to estimate trends in change in glacial thickness between 2003 and 2009 on the whole Tibetan Plateau. Considering acquisition conditions of ICESat measurements and terrain surface characteristics, annual glacier elevation trends were estimated for 15 different settings with respect to terrain slope and roughness. In the end, we only included ICESat elevations acquired over terrain with a slope below 20° and a roughness at the footprint scale below 15 m. With this setting, 90 glaciated areas could be distinguished. The results show that most of observed glaciated areas on the Tibetan Plateau are thinning, except for some glaciers in the northwest. In general, glacier elevations on the whole Tibetan Plateau decreased at an average rate of -0.17± 0.47 m per year (m a-1) between 2003 and 2009, taking together glaciers of any size, distribution, and location of the observed glaciated area. Both rate and rate error estimates are obtained by accumulating results from individual regions using least squares techniques. Our results notably show that trends in glacier thickness change indeed strongly depend on the relative position in a mountain range.