青藏公路沿线冻土区域分布计算机模拟与制图

Computer Simulation and Mapping of the Regional Distribution of Permafrost along the Qinghai-Xizang Highway

通过对青藏公路沿线实测年平均地温多元回归统计 ,建立了年平均地温与海拔、纬度的关系模型 .利用多年冻土分布下界的统计方程和关系模型及基于格网的地理信息分析系统 ,对青藏公路沿线多年冻土下界分布和多年冻土地温带分布进行计算机模拟 .结果表明 ,所建立的模拟模型能够反映青藏公路沿线多年冻土的区域分布特征 ,模拟结果基本上反映多年冻土分布状况 .

Distribution of permafrost in the Qinghai-Xizang Plateau is characterized by a zonation of three-dimensions. By using a method of curve fitting, an empirical correlation between lower limit of high altitude permafrost ( H L) and latitude (φ) has been obtained in the Northern Hemisphere. It can be expressed as:H L =3 650 exp [-0.003(L-25.37) 2\]+1 428(1)The model is certificated by some data along the Qinghai Xizang Highway, showing that it can precisely reflect the lower limit distribution of permafrost along the Qinghai Xizang Highway. At the same time, the traditional one dimensional permafrost model cannot be applied for regional permafrost mapping along the Qinghai Xizang Highway because of great regional difference in surface characteristics. Modeling the distribution of permafrost along the Qinghai Xizang Highway must consider high altitude permafrost characteristics, permafrost vertical zonation, and mean annual ground temperature (MAGT). The following equation is used to calculate the MAGT on each grid:T z =68.827-0.00827H-0.927L(2)Where T z is MAGT, H is the altitude (m), L is latitude(φ).This equation is based on arelationshipamong MAGT, altitude and latitude. It is obtained by using ground temperature measurements along the Qinghai Xizang Highway. The regression coefficient is 0.96 for 40 data series. Five types of permafrost stability are classified according to MAGT. MAGT of each grid along the Qinghai Xizang Highway is computed from Equations (1)、 (2) and DTMs. Then, a map showing ground temperature zones is obtained according to MAGT of each grid and permafrost classification. For thawed areas in permafrost regions, it is difficult to be modeled by the model. So, the distribution of thawed areas is obtained by digital mapping and overlaying it in the map of ground temperature zone. The result of mapping shows that the model of lower limit distribution of permafrost and ground temperature zone in permafrost can precisely describe the distribution characteristics of permafrost along the Qinghai Xizang Highway. The upper zone of permafrost generally exists in high mountainous areas, middle zone exists in Chumaer River high plain areas, mountainous base areas and valley areas, and the lower zone do not exist alone the Qinghai Xizang Highway. This result agrees with the realistic state of permafrost distribution and the effectiveness of the model is verified.