6. Landscape, Lake Distribution, and Evolution in Eastern Mongolia

Eastern Mongolia is characterized by a unique landscape of the endless vast Dornod plain encompassed by the Khentii Mountain Range in the northwest and the Khyangan Mountain Range in the southeast, with a large lake called Lake Buir and many small lakes, which is in stark contrast to other regions of Mongolia. Lakes, rivers, and streams in the region play important role in the surface water resource in the Pacific Ocean drainage basin. In eastern Mongolia the greatest number of lakes in the country (28.9%) are distributed, and these lakes are dominantly fluvial, thermokarst, aeolian, and glacial lakes. Lakes residing in the valleys and depressions in this region under the arid climate have primarily fluvial and thermokarst origins with exceptions of a few tectonic and moraine-dammed lakes. The lakes in the east, south, and west of this region are shallow and saline, and they are strongly dependent on precipitation. However, lakes in the north of the region are deep and freshwater, and they are fed by precipitation, runoff, permafrost meltwater, and groundwater. Many lakes in this region are shifting to playa environments in recent years due to the rising temperature and strengthening evaporation. Eastern Mongolia was under the strong influence of the East Asian Summer Monsoon during the Pleistocene and early Holocene, but it has been under the influence of the East Asian Winter Monsoon since the middle Holocene. This shift in the atmospheric circulation is followed by the arid climate in the late Holocene and the present warming is causing drought. These recent conditions are distinctly reflected in the evolution of landscape and surface water, particularly for lakes of eastern Mongolia today.