Analysis on trend and causes of Spring-Summer consecutive drought in Yunnan province.
Analysis on trend and causes of Spring-Summer consecutive drought in Yunnan province.
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发表时间：
2010
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通讯作者：
Peng Gui-feng;Zhao ErXu;Zhou Guo-lian
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作者：
Peng Gui-feng;Zhao ErXu;Zhou Guo-lian
根据全省受旱面积和不同干旱强度等级，构建区域干旱指数，用异常指数划分中、重、特旱年，利用NCEP/NCAR再分析资料，用Morlet小波分析云南省春夏连旱强度指数的变化趋势，并对春夏连旱灾害年与多年平均值的200 hPa、500 hPa环流差异进行了比较分析。结果表明，云南省春夏连旱灾害发生的平均频率为：20年一遇特大干旱，10年一遇重旱，5年一遇中旱，目前云南可能处于这样的历史位置，要么没有春夏连旱，要么将是特大干旱灾害，500百帕高纬受纬向环流控制，青藏高压明显偏弱，孟加拉湾低槽不出现或明显偏弱，20°N以南地区受正距平带控制，200 hPa青藏高原处于-50 gpm强负距平区，中南半岛北部处于-5 gpm异常带，这些情况不能形成以中南半岛北方和南海北部为中心的垂直环流。高层辐散增强，低层辐散增强，缺乏有效降水过程缓解干旱，东西季风转换较常年偏晚16 d，造成云南春夏连旱。
By constitution of Regional Drought Index concerning drought-hit area in the whole province and different levels of drought intensity,we have used Abnormal Index to divide years into moderate,heavy and super drought ones.Based on NCEP/NCAR reanalyzing data,we have used morlet wavelet to investigate the trends of Intensity Index of Spring-Summer consecutive drought in Yunnan Province,as well as to compare and analyze the difference in 200hPa and 500hPa circulation between the disastrous years of Spring-Summer consecutive drought and multi-year’s average value. The results show that average frequency of Spring-Summer consecutive drought causing disasters in Yunnan Province is:Super drought happens once in 20 years,heavy once in 10 years,and moderate once in 5 years.At present,Yunnan may be in such a historical position,either there is no Spring-Summer consecutive drought,or will be a super drought disaster.The 500hPa high latitudes is controlled in zonal circulation,and Qinghai-Tibet high-pressure is obviously weak,and the bay of Bengal low trough does not appear or obviously weak.The south area of 20°N is controlled by positive anomaly zone,and has not convergence of cold and warm air in Yunnan.The 200hPa Qinghai-Tibet Plateau is in -50gpm strong negative anomaly zone,and the north part of Indo-China Peninsula is in -5gpm anomaly zone.These situations can not form the vertical circulation with a center in the northern part of Indo-China Peninsula and the upper-level divergence as well as the low-level divergence rising,which means that there is not an effective precipitation process to relive the drought.In addition,the east-west monsoon transition is later about 16d than usual,which bring on the Spring-Summer catastrophic consecutive drought in Yunnan province.