1960—2013年北京旱涝变化特征及其影响因素分析

基于1960—2013年北京及其周边34个气象站点逐日降水数据,利用标准化降水指数(SPI),辅以小波分析、滑动平均和相关分析等气候诊断方法,论文分析了近54 a北京旱涝变化特征,探讨了城市化和大气环流异常与旱涝变化的关系。结果表明:1近54 a北京轻微旱涝事件呈减少趋势,极端旱涝事件逐渐增多;2在年代变化上,20世纪60—80年代SPI值呈稳定波动,80年代中后期SPI值呈下降趋势,涝灾逐渐减少,旱灾逐渐增多,1999—2008年形成10 a连旱的降水偏少期;3快速城市化对北京旱涝变化影响明显,但是并未改变旱涝宏观变化趋势;4 ENSO与北京旱涝变化关系存在不稳定性,El Nio事件并非严格对应旱灾,La Nia事件并非严格对应涝灾;副热带高压位置和东亚夏季风强弱与北京旱涝变化关系相对稳定。当副热带高压明显北移、东亚夏季风偏强时,北京多发生干旱;反之,则北京明显偏涝。

The Characteristics of Drought-Flood Variation and Its Influence Factors in Beijing during 1960-2013

Using the daily precipitation data of 34 meteorological stations in Beijing and its surrounding areas, this paper attempts to describe the variation trends of drought-flood in Beijing in different seasons during 1960-2013. Based on Standardized Precipitation Index (SPI), correlation analysis, Morlet wavelet analysis and other climate diagnosis method, we analyzed the influence factors of drought-flood variations. It is found that the number of minor drought-flood events decreased, while that of the severe drought- flood events increased during that period, which indicates that drought and flood events were becoming more extreme. At short- time scales, SPI fluctuated greatly, which means that drought and flood alternated frequently. At long-time scales, droughts and floods alternated frequently before the 1980s; after the middle of 1980s, SPI was going down, so that the number of flood disasters decreased, while the number of drought disasters increased gradually. Since there was little precipitation during 1999- 2008, the continuous drought occurred during the past decade. The urbanization process had obvious effect on the intensity of droughts and floods, but it did not affect the interdecadal variation. The relationship between drought-flood and El Niño-Southern oscillation (ENSO) is unstable. During the El Niño before 1980s, precipitations in summer showed a decreasing trend, leading to a severe drought in Beijing. With the emergence of the anomalous convection over the western North Pacific after the 1980s, the relationship became weak. The western Pacific subtropical high and East Asian summer monsoon showed relatively stable relationship with the variation of droughts and floods in Beijing: when the East Asian summer monsoon was stronger than normal and the western Pacific subtropical high went more northward, continuous droughts occurred in Beijing, whereas the reverse would cause flood.