云南春夏连旱气候变化趋势及致灾成因分析

通过构建能同时考虑全省受旱范围(面积)和不同等级干旱强度的区域干旱指数,用异常指数划分出云南中、重和特旱年份,利用NCEP/NCAR再分析资料,采用morlet小波研究了云南春夏连旱强度指数的变化趋势,并对比分析了云南春夏连旱重灾年与多年平均200hPa与500hPa环流场的差异.结果表明:云南春夏连续致灾干旱的平均出现频率是:特旱20a一遇,重旱以上10a一遇,中旱以上5a一遇;目前云南可能处于这样的历史位置,要么是不出现春夏连旱,如果出现,则将是特旱灾害;500hPa高纬度为纬向环流控制,青藏高压明显偏弱,孟加拉湾低槽没有出现或明显偏弱,20°N以南地区为正距平区控制,无冷暖气流在云南交汇,200hPa青藏高原上为-50gpm的强负距平区,中南半岛北部处于-5gpm距平区,形不成中心在中南半岛北部的高层辐散、低层辐合上升的垂直环流,使云南不能出现解除干旱的有效降水天气过程,东西风季节转换较常年偏晚16d左右,导致了云南春夏连续致灾干旱的发生.

Analysis on trend and causes of Spring-Summer consecutive drought in Yunnan province

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 in200hPa 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 in20 years,heavy once in10 years,and moderate once in5 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 500hPa 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°Nis controlled by positive anomaly zone,and has not convergence of cold and warm air in Yunnan.The 200hPa Qinghai-Tibet Plateau is in -50gpm strong negative anomaly zone,and the north part of Indo-China Peninsula is in -5gpm 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.