Impacts of Climate Warming and Human Activities on Permafrost in the Hovsgol Mountain Region, Mongolia
Sharkhuu Anarmaa, Natsagdorj Sharkhuu, Bernd Etzelmuller, Eva S. Flo Heggem and Clyde E. Goulden
The Hovsgol Mountain Region is located between the coordinates of N 49°-52° and E 98°-102°, in territory of Hovsgol Aimag, Mongolia. The territory is characterized by mountain permafrost, island to continuous in its distribution, and occupies the southern fringe of the Siberian continuous permafrost zones. According to data collected by the Hatgal weather station, during the last 40 years the mean annual air temperature has increased by 1.86°C. The impacts of human activities on permafrost are caused by different kinds of land use such as livestock grazing pressure, forest fires and cutting, mining exploitation and different engineering construction.
The objectivities of the study on permafrost monitoring in the region are to estimate rates of permafrost degradation under influence of climate warming and to analyze some impacts of human activities on permafrost degradation.
In recent years the impacts of climate warming and human activities on permafrost in the region are monitored within the framework of CALM and GTN-P programs and Hovsgol GEF/WB Project. In addition, we have started measurements for estimating thaw settlement and permafrost temperature gradient in the Darhad depression, to the west of Hovsgol.
The main parameters of permafrost monitoring are active layer depth and mean annual permafrost temperature as well as permafrost temperature gradient. At present, there are 17 both CALM and GTN-P monitoring boreholes in the region. All data are added to these international databases for observations on changes in permafrost conditions from all over the World. Some of the Hovsgol boreholes with a depth of 10-15 m were redrilled and instrumented to depths where previous deep temperature measurements in the original holes were made 17-35 years ago.
The observed rate of increase in active layer thickness varies from 3 to 25 cm per decade, and the rate of increase in mean annual permafrost temperature varies from 0.2°C to 0.4°C per decade, depending on local landscape and ground conditions. Long-term monitoring of permafrost shows that permafrost is degrading more intensively during the last 15 years than during the previous 15-20 years (1970-1980s). The widespread thermokarst lakes, depressions, hollows, and intensive thermo-erosional riverbanks in the Darhad depression are direct indicators of ancient and recent degradation of permafrost under climate warming.
Initial data on short-term monitoring of permafrost in six valleys along the northeastern shore of Lake Hovsgol show that active layer thickness varies from 1.4 m in Dalbay valley in the south to 4.8 m in Turag valley in the north. Meanwhile, permafrost temperature at a depth of 10 m varies from -1.25°C in Dalbay valley to -0.42°C in Turag valley. As compared to Turag valley, the shallow active layer and low permafrost temperature in Dalbay valley are apparently caused by livestock grazing pressure.
Vegetation cover acts as a cooling factor and reduces the average annual surface temperatures. In comparison with bare steppe where grasses have been cut by mowing, leaving little vegetation cover,, the values of decrease in mean summer surface temperatures are to be estimated by about 2.2°C under dense grass, 3.6°C under sparse forest and dense shrubs, 4.9°C under dense forest and bushes, and by 6.4°C under 10 cm thick moss cover at the Dalbay observation sites. Moss cover, dense grass, and forest are natural insulators, protecting soil moisture from high evaporation and maintaining low soil temperatures. These preliminary results suggest that the key to preserving permafrost and ecosystems, especially in the Hovsgol taiga zone, must be based on protection of vegetation cover.
In general, the permafrost in the Hovsgol Mountain Region is degrading more intensively than in the Khentei and Khangai Mountain Region, but less intensively than in the Eastern Siberia and even in the Trans Baikalia.