西安地区近五百年旱涝变化趋势与近百年旱涝成因分析

Trends of Drought and Flood in Recent 500 Years and Their Causes in Recent 100 Years in Xi'an

根据历史文献、站点资料对西安地区五百多年的旱涝等级序列进行了重建和统计分析,并利用ERA-20C再分析数据,并对近百年(1900—2008年)不同旱涝等级的气象条件进行了合成分析。结果表明:西安旱涝等级随时间有向偏涝发展的趋势,旱涝年的环流形势有明显的差异,体现在极涡、阻高、低槽及北大西洋涛动等方面均呈相反的形态;水汽输送差异主要在7月和9月的纬向水汽输送通量,动力作用与南亚高压的位置和强度紧密相关,呈现出非常明显的差异。造成旱涝年前期冬末初春的环流背景和海温也具有显著的不同,总体来说,涝年前期伴随了较强的冷空气活动,而旱年大气活动相对平稳;东太平洋和北大西洋海温异常,对旱涝年的大气响应主要表现在副热带高压强弱位置的差别和北大西洋涛动位相的不同。

In this paper,the drought and flood levels in Xi＇an in recent 500 years were rebuilt and analyzed using the historical documents and precipitation data. It was found that the variation of drought and flood levels in Xi＇an was aperiodic,and it trended from normal to flood. Nearly recent 100-year reanalysis data were used to investigate the circulation background,moisture and dynamic conditions affecting the drought and flood years. The results showed that the circulation background was significantly different from different years,and the polar vortex,blocking high,trough,North Atlantic Oscillation were opposite. Differences of water vapor transport was mainly affected by zonal water vapor transport flux in July and September,and of dynamic effect by the location and intensity of South Asian anticyclone. The causes of drought and flood in late winter and early spring were significantly different,including mainly the circulation background in atmosphere and sea surface temperature.