Permafrost Distribution in Eastern Tibet: Variation of the Active Layer Thickness and its Effect on the Soil Drought

 

In Huanghe (The Yellow River) in China, which provides the water demand for the Huabei province, the increase of irrigation in the middle reaches causes the water shortage in the downstream. In addition, drought and decrease of the grassland are pointed out in the source region. Based on these concerns on water resources, a network of observation on the ground water runoff is going to be set up in Huanghe drainage basin, as a part of the project "The development of the predictive model for change of water resources due to artificial alteration of environment in Asian Monsoon area" (founded by the Ministry of Education, Culture, Sports, Science and Technology of Japan).

For the monitoring/predicting of the water resources, it should be taken into account that source area of Huanghe is underlain by discontinuous permafrost, because permafrost distribution is the dominant controlling factor of ground water runoff. It is observed that mean annual temperature of the region has been increasing by 0.025°C/year since 1950s, thereby the degradation of the permafrost is considered to be one of the causes of drought. However, there is no direct observation of the distribution and temporal variation of the active layer thickness.

The project is aimed to investigate the relationship between variations of active layer and soil moisture distribution; Ground temperature and soil moisture observation with 15m-depth borehole is starting from August 2004. Other three 3m-depth shallow boreholes will be also installed for the comparison with different surface conditions.