The Multidecadal Variability Of Precipitation And Its Response To Greenhouse Over Arid And Semi-arid Region Of Northern China

Arid and Semi-arid region of China accounts for about 52%,which is mainly located in Northern China.The climate characteristics are dry climate, large variable precipitation and extrem fragile ecosystems. Nowadays, issues include the climate change and mechanism, quantitative assessment to climate of natural factors and human activity has attracted more and more researchers to study. In this paper, I mainly analyze the multidecadal changes and human activities affection to precipitation in arid and semi-arid region of northern China. The purpose is to give a scientific reference for climate prediction. Firstly, based on the data of both GPCC_V7 and ERA₂0C monthly precipitation, mainly using ensemble empirical mode decomposition?EEMD?and composition analysis method to analyze the multidecadal change of arid and semi-arid region in northern China and the relationship between MDV and Pacific Decade Oscillation?PDO?.Secondly, based on the industrialization/present radiative forcing thousand datas obtained from CCSM4.0 model experiment, to assess the impact of human activities to the precipitation and air-sea interaction. The result shows:?1? The precipitation of arid and semi-arid region in northern China has a multidecadal variability with about 50-60 years mean period which may be modulated by PDO. The northern Xinjiang and Inner Mongolia is significant positive correlation, while the east and west to Hetao is significant negative correlation.?2? The possible mechanism shows, the strengthening of meridional circulation make water vapor of Arctic Ocean flow southward on positive PDO phase. As a result, the precipitation of Xinjiang is increased by the converging of northwest cold-wet flow from Arctic Ocean and southwest warm-wet flow from Arabian Sea in southern Xinjiang. On the other hand, the convection heating of equatorial western Pacific Ocean and Indian Ocean led to the Pacific-Japan/East Asia-Pacific?PJ/EAP? pattern of teleconnection. It is benefit to transport wet flow from Bohai sea to northern area and increase precipitation on positive PDO phrase. The conclusion is the opposite on the negative PDO phrase.?3? CCSM4.0 model simulates high rainfall in arid and arid-semi region, but can stillsimulates the spatial distribution of precipitation. The results is that human activities?B2000-B1850? can cause precipitation increasing especially in the southern Xinjiang and Qinghai.The summer precipitation is important for Xinjiang and Qinghai precipitation increasing most,while the spring may be magnify this precipitation center because of the false precipitation center in this area.?4? Based on the result of CCSM4.0 model data analysis, the main spatial distribution of precipitation?the first mode of EOF analysis? is positive distribution with the center in mid-eastern of Inner Mongolia, which positive correlation with East Pacific SSTA and negative correlation with West Pacific SSTA.Besides the positive correlation is enhanced, while the negative correlation is weakened by the greenhouse gas increasing in the past hundred years.The second EOF mode shows that, the distribution is flood in the west and drought in the east. It is can be enhanced by greenhouse gas increasing caused that there is the positive correlation with tropic Indian ocean and negative correlation with western Pacific to northeast and southeast ocean,while the positive correlation with East Pacific can be weakened by greenhouse gas increasing. As a result, it lead to the rainfall in Western region increasing and the rainfall in astern region decreasing.