Study On The Spatial And Temporal Distribution Characteristic Of Precipitation And Numerical Simulation In Qilianshan Mountains, N.W. China

Geomorphic evaluation is dominated by the interaction between climate, tectonics and erosion. Previous studies show that climate is an indispensable constituent part of study on geomorphic evaluation which has an effect on the erosion process. Meantime, precipitation is the key factor to study the interaction between climate and the surface process. Therefore, it is very important to research on the spatial and temporal distributions of precipitation in the hypsographic mountain areas for studying geomorphic evaluation.Based on investigate the climate change in the past50years in Qilianshan Mountains, and then pays more attention on different spatial and temporal distribution characteristic of precipitation and the relationship between precipitation and topographic factors. First, the author uses the meteorological data from1961to2010to analyze the variation of the temperature and precipitation. Then, precipitation and topography data of two separate research areas (the Xiying river basin and the Qilianshan Mountains) are used to study the precipitation distribution and to analyze the relationship between precipitation and the topographic factors (the max altitude, the min altitude, the mean altitude and mean local relief). At last, the author investigates the thermal and dynamic effects on the precipitation distribution by simulating a precipitation event with WRF3.1(Weather Research Forecasting v3.1). The main contents and results are as follows:(1) There is a warming and humidification trend in the past50years in the Qilianshan Mountains. The results show that temperature and precipitation increased in most meteorological stations, but the rate of warming and humidification is various in different areas, which is greater in central Qilianshan Mountains than in the west and the east. Therefore, the central of the Qilianshan Mountains might be the transitional region of climate change.(2) In the Xiying river basin which is in the eastern Qilianshan Mountains, the convection plays an important role in precipitation process. The relationship between topography and precipitation shows the precipitation increases with the increasing of the altitude, and the correlation coefficient between the precipitation and the min altitude is larger than that and the other topographic factors. Therefore, there is always an obvious local convective precipitation in a small time scale precipitation process.(3) The relationship between topography and annual mean precipitation shows that the precipitation intensity increases as the altitude increases in the Qilianshan Mountains. The max annual mean precipitation intensity in the west, middle and east of the Qilianshan Mountains is200mm,400mm and700mm, respectively. From the foot of mountains, precipitation increases as the altitude increases and the max precipitation appears on the ridge. However, there is no obvious relationship between the precipitation and the topography in the inner of the mountains. Compared with the relationships between precipitation and the other topographic factors, the max altitude might play the most important role than the others, when the correlation coefficient between precipitation and the max altitude in the west, middle and east of the Qilianshan Mountains is0.82,0.74and0.80, respectively. The effect that the mean local relief is on the precipitation in the eastern Qilianshan Mountains is greater than that in the middle and the west of the Qilianshan Mountains.(4) The precipitation process depends primarily on the westward stream transferring vapour to the north-western of China. The precipitation distribution in the mountain areas is affected by the large-scale transportation of vapour and the local convection. The experiment shows that the mesoscale model (WRF3.1) has the ability to simulate the precipitation process in the Qilianshan Mountains, and the scheme of G3-Ferrier-NOAA is the best. In the precipitation process, the low mountain areas are more stability than the alpine region where there is a fierce convection. Low layer (800hPa) is the major transfer route of vapour from water source and westward stream plays an important role in the vapour conveying during the summer in the west-northern China.