Hydrological and geomorphological basin and catchment characteristics of Lake Nam Co, South-Central Tibet

For Lake Nam Co, south-central Tibetan Plateau, geomorphological features and hydrological characteristics have been compiled to provide an overview of the landscape character. Information is based on primary data, collected during field campaigns in the summers of 2005 and 2006, and secondary data as available from satellite images. Nam Co is located at the intersection of the Westerlies, the winter monsoon, the South West Asian monsoon, and the East Asian monsoon. It is situated in a graben structure. Landforms of the drainage basin are highly influenced by tectonics, superimposed by fluvial and periglacial processes, and locally by glacial and aeolian processes. Its drainage basin is endorheic. Thus, lake level is primarily controlled by the balance between input through precipitation or inflow streams and evaporation as the output. The significance of lake water evaporation is evidenced by the salinity and measurable increase of 2H and 18O of the lake water when compared to the inflow streams and precipitation. Maximum conductivities total 431 μS mm−1 for the inflowing river waters and 1920 μS mm−1 for the lake water. Overall, the solute contents are low and characterise Nam Co as a pristine environment. Dominant ions are calcium and bicarbonate in river waters. Sulphate contents are relatively high in Nam Co, and the lake is also characterised by high boron values. A significant decrease in lake water salinity during the past two decades is likely related to increased freshwater input.