Inter-decadal Characteristics of Aridification over Northern China Associated with the Variation of Atmospheric Circulation During the Past 50 Years
Aridification over northern China is currently one of the most urgent living environmental issues in our country. A lot of studies have been carried out concerning its evolution, causes and prediction, etc. There are different general circulation patterns at each dry/wet stages undouhtedly. In other words, an abrupt adjustment of summer monsoon circulation over East Asia will result in a distinct change of the precipitation pattern. However, up to now, analyses on the relationship between northern China drought and the summer south wind have been very limited. In this paper , inter-decadal characteristics of aridification over northern China and its association with the variation of atmospheric circulation during the past half century are analyzed based on the latest ECMWF and CRU reanalyzed monthly grid data. To better describe the detailed temporal and spatial features of droughts in northern China, the northern China is divided into 4 sub-regions and the annual Palmer Drought Severity Index (PDSI) is calculated in every unit respectively. It is shown that the annual precipitation and PDSI have decreased significantly in sub-regions B and C over the past 50 years. While in sub-region A, the annual precipitation and PDSI have an increasing tTend from the end of 1950s to the mid 1990s followed by a decreasing period. In sub-region D, the annual precipitation and PDSI have a significantly decreasing trend from the end oi 1950s to the end of 1970s, and increasing trend from the beginning of 1950s to mid 1990s followed by a decreasing period. As a matter of fact, it should be pointed out that the results in sub-region A may not be reliable enough as Wei Jie et al. suggested that PDSI is not suitable for extreme drought and wet regions. Therefore, the physical mechanism of drought in sub-regions B and C is mainly discussed with focusing on the inter-decadal adjustment of summer monsoon circulation over East Asia. Multiple data analyses reflect the evident climatic jump at the end of 1970s over northern China. Accordingly, an inter-comparison of summer south wind, water-vapor transport and the 850 hPa anticyclone intensity between two periods is conducted. It is indicated that the south wind had experienced a strong period from 1958 to 1976 and then a weak period from 1977 to present. As a result, the precipitation distribution over northern China during the concerned periods altered obviously due to changes of the water vapor supply. Analyses on the 850 hPa anticyclone intensity present a similar conclusion. All these studies show that the aridification over northern China results from multiple factors: the weakened East Asian summer monsoon, the reduced water-vapor transport, and the increased anticyclone intensity, and so on.
aridificationwater-vapor transportEast Asian summer monsoonnorthern China
国家科技期刊平台
NSTL
万方数据
维普
