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Water Level Rise in Lake Khuvsgul in the Permafrost Region of Mongolia                   – its Causes and possible Countermeasures – 

1) Introduction
   The water level of Lake Khuvsgul has risen 80cm in the recent 40 years, so that the surrounding forest, pasture and the lakeshore town have been inundated year by year. Climate change studies in Mongolia have showed that the average air temperature has increased by 1.56 degrees Celsius during the last 60 years, while the annual precipitation has decreased since the 1940s (Batima and Dagvadorje, 2000). However, the increasing lake level in the western part of Mongolia since the 1980s caused by melting of glaciers and thawing of permafrost due to global warming (Batnasan, 2001). In order to clarify the thawing of permafrost around the lake induced by the progress of global warming, the ground temperature profiles were measured in August of 2001 and 2002.
2) Ground Temperature

   L. Khuvsgul is surrounded by forest mainly to consist of Larix Sibirica and pasture. It is said that the forest has been suffering by the man-made fire due to the recent poaching, so there are three kinds of the fundamental land-use such as forest, fired forest and pasture.

We found that there is the typical ground temperature profiles in relation to the land-use patterns. The temperature below 1m in the forest area is 0 ℃, so it shows that the thickness of the active layer is 1m and there is the permafrost layer below it, while the temperature below 1m in the fired forest 6 ℃ and that in the pasture 11 ℃. Using the temperatures gradient, the thickness of the active layer was predicted by the calculation to investigate the influence of the land-use patterns. As the results, that in the fired forest about 2m and that in the pasture about 4m reflecting the absorption rate of the incoming solar radiation.

Therefore, the fired forest as well as the pasture mainly caused by the anthropogenic land-use significantly influences the ground temperature profile in which the ground temperature increases and thaws the permafrost, so that the water level of L. Khuvsgul are supposed to increase. It is obvious that the forest has an important role to preserve the permafrost layers by interrupting the incoming radiation and also the ground vegetation can use the active layer as water resource. The relationship is a good example as the symbiosis, however it should be noted that the important relationship has been recently deteriorating by an enlargement of the fired forest and the pasture.

On the other hand, there is only one out-flowing river from L. Khuvsgul at the southern end. At that place, it was found that a large amount of sand and gravel has accumulated and has formed a natural dam in the out-flow river by the transportation from the tributary river which is heard to happen at the heavy rain. It is undoubted that the dam is also one of the main causes of the water level rise.

3) Concluding Remarks

   Consequently, three causes of the water level rise could be noticed as follows: 1) the formation of a natural dam at the southern end of the lake caused by the sedimentation of sand and gravel which were transported from the tributary river at the time of heavy rain; 2) the thaw of permafrost around the lake where the ground temperature becomes higher with increases of the incoming radiation due to deforestation owing to the anthropogenic expansion of pasture and fired forest; 3) the thaw of permafrost caused by the global warming. The climate warming and the anthropogenic land-use influence on thawing of the permafrost and rising the water level of L. Khuvsgul.

Based on the above-mentioned results, we would like to suggest as the short-term countermeasure that the natural dam should be dredged to prevent the inundation, because it can be estimated to lower 30cm of the water level by the dredging of only 500m3. As the mid-term countermove, it is important to improve anthropogenic land-use for preventing the expansion of pasture and fired forest. Finally, as a long-term issue, we hope to solve the global warming with the international cooperation by monitoring the natural environmental changes of L. Khuvsgul.

So, it is obvious that the influence of climate warming and fired forest is quite eminent and vulnerable to the environmental conditions of L. Khuvsgul in the permafrost region of Mongolia.

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References

Batima P. and Dagvadorje D. (2000) Climate change and its impact in Mongolia. National Agency for Meteorology, Hydrology and Environment Monitoring and JEMR Publishing, pp. 227.

Batnasan N. (2001) Water level increases in Lakes Uvs and Uureg, Mongolia. Proceedings of International Symposium on Mountain and Arid Land Permafrost, Ulaanbaatar, Mongolia, 4-5.