Changes in surface area of the Böön Tsagaan and Orog lakes (Mongolia, Valley of the Lakes, 1974–2013) compared to climate and permafrost changes

• The Böön Tsagaan and Orog lakes are formed in the area of permafrost occurrence.
• Lakes in Central Mongolia are subjected to seasonal shrinkage or drying out.
• Climate changes lead to transformation of water conditions in the Valley of the Lakes.

The main aim of the study is the analysis of changes in surface area of lake Böön Tsagaan (45°35′N, 99°8′E) and lake Orog (45°3′N, 100°44′E) taking place in the last 40 years in the context of climate conditions and permafrost degradation. The lakes, located in Central Mongolia, at the borderline of permafrost range are fed predominantly by river waters and groundwater from the surrounding mountain areas, characterized by continuous and discontinuous permafrost occurrence — mostly the Khangai. The analysis of the Böön Tsagaan and Orog lake surface area in 1974–2013 was conducted based on satellite images, whereas climate conditions were analysed using the NOAA climate data and CRU dataset. Principal Component Analysis (PCA) was used to study the relationship patterns between the climatic factors and changes in the surface area of the lakes. A tendency for a decrease in surface area, intermittent with short episodes of resupply, was observed in both studied lakes. Climate changes recorded in the analysed period had both direct and indirect impacts on water supply to lakes. Taking into account the results of PCA analysis, the most significant factors include: fluctuation of annual precipitation, increase in air temperature and thickness of snow cover. The extended duration of snow cover in the last decades of the 20th century may constitute a key factor in relation to permafrost degradation.