1951－2015年洞庭湖区旱涝演变及典型年份旱涝急转特征分析

旱涝灾害是制约洞庭湖区经济发展的重要因素,为预测湖区旱涝灾害变化趋势,该文选取1951-2015年洞庭湖区及其周边地区35个气象站点的逐月降水量数据,利用标准化降水指数和夏季长周期旱涝急转指数,辅以小波分析方法,分析近65 a来研究区域的旱涝演变及典型年份旱涝急转特征.结果表明:该区旱涝事件发生的频率高,不同时间尺度旱涝事件发生的平均频率为42.62%.在季节尺度上,夏季洪涝事件发生的频率最高,为33.33%,冬季干旱事件发生的频率最高,为41.54%;在年代际尺度上,20世纪70年代干旱事件发生的频率最高,为25.83%,其次是2001-2015年,频率为22.99%,90年代洪涝事件发生的频率最高,为30%.该区域旱涝变化有4个特征时间尺度,分别为4、10、25和31 a,预测湖区在未来几年降水偏多.洞庭湖区3个区域的旱涝变化大抵一致,但在不同时期仍存在一定的差异.湖区近65 a来有15 a的LDFAI绝对值大于1,旱涝急转现象较频繁,不管是旱涝变化还是旱涝急转变化,东、西洞庭湖区的变化趋于一致,南洞庭湖区与东洞庭湖区旱涝急转变化差异较大.

Analysis on evolution of drought-flood and its abrupt alternation in typical year from 1951 to 2015 in Dongting Lake area

Abstract: Drought-flood disaster is one of vital factors restricting Dongting Lake area''s economic development. In order to predict the future drought-flood change tendency, using the monthly precipitation data of 36 meteorological stations in Dongting Lake and its surrounding areas, this paper attempted to describe the characteristics of evolution of drought-flood and its abrupt alternation in typical year from 1951 to 2015 in Dongting Lake area. Standardized precipitation index (SPI) and long cycle drought-flood abrupt alternation index (LDFAI), Morlet wavelet analysis and other climate diagnosis method were adopted. The results showed that the variation of drought and flood could be roughly divided into 5 periods. The first period was from 1951 to 1955, which was relatively humid. The second period was from 1956 to 1970. In this period, the alternation of flood and drought was frequent and the calamity degree was not severe. The third period was from 1971 to 1990. The alternation was also frequent and the calamity degree was severer than the previous period. The fourth was a humid period from 1991-2003. The last was an arid period after 2003. In this period, drought disaster has showed an obvious increasing trend. In the study area, flood and drought occurred frequently, and its alternation was also frequent during 1951-2015. The average frequency of different time scales of drought and flood events was 42.62%. The distribution of precipitation was uneven and concentrated in summer. The highest frequency of flood events was 33.33%, which occurred in summer. In winter, the frequency of drought events was 41.54%. Flood events showed an increasing trend in spring and summer in the 1990s. But in recent years, the rainfall has kept decreasing in 4 seasons. On an interdecadal scale, the 1990s was the wettest decade and had the highest frequency of flood events which was 30%. The precipitation was the least and the frequency of drought event was 22.99% in 2001-2015. In this period, the frequency of extreme drought event was the highest. The highest frequency of drought events was 25.83% in the 1970s. In this period, the precipitation was also low. Variation of drought-flood had 4 characteristic time scales, respectively, 4, 10, 25 and 31 a, which revealed that Dongting Lake area would be have more precipitation in the next few years. The variations of drought-flood in the 3 areas including East, West and South Dongting Lake area were basically the same, but had some differences in different periods. The variation of drought-flood even showed an obviously reverse phase in South and West Dongting Lake area in 1990s. There were 15 years with the absolute value of LDFAI is greater than 1 in recent 65 years in this area, which meant drought- flood abrupt alternation phenomenon was frequent. For either the variation of drought-flood or its abrupt alternation, West Dongting Lake area and East Dongting Lake area were basically the same. The variation of drought-flood abrupt alternation in South Dongting Lake area was obviously different from East and West Dongting Lake area.