2011年长江中下游春旱的气候特征分析

利用我国高分辨率逐日降水资料，从降水量、无降水日数、连续无降水日数、气象干旱指数（CI）等指标对2011年春季长江中下游地区发生的气象干旱进行了分析评估。结果表明，2011年春季长江中下游地区降水量为近60 a同期最少，无降水日数、气象干旱影响范围均为近60 a同期最大，重度以上气象干旱日数为近几十年来同期罕见。此次严重气象干旱具有强度强、持续时间长、干旱范围广、影响程度重等特点，为近60 a来长江中下游地区春季发生的最严重的气象干旱，对水资源、水产养殖业、农业生产等造成了重大影响。还从大气环流、水汽输送角度对气象干旱的成因进行了初步分析，认为2011年冬春季北方冷空气势力强大，向南扩张明显，南方热带对流系统不活跃，向长江中下游地区水汽输送弱，是造成此次气象干旱的主要原因

CLIMATE CHARACTERISTICS OF THE 2011 SPRING DROUGHT IN THE MID LOWER YANGTZE BASIN

Climate change is accelerating and leading to climate and weather extremes around the world.Climate and weather extremes such as severe droughts,destructive flooding,heat waves,etc accounted for more than 90% nature disasters in 2011.Statistical analyses showed that the loss caused by drought rank first among all the meteorological disasters.Previously,most attention has been paid to analyze the time space characteristics of drought in northern China and much less has been paid to the Yangtze Basin.In spring of 2011,however,a severe drought occurred in the mid lower basin of the Yangtze River. Based on the daily precipitation data from 1951 to 2011,the seasonal precipitation anomalies,no rainfall days,continuous no rainfall days were calculated to compare the severity of the 2011 spring drought.By calculating the grades and extent of the Compound Index of meteorological drought (CI),the historic comparison of the intensity of 2011 spring drought was made in the study.It is shown that spring of 2011 had much less precipitation than normal,creating the least record since 1951.Prolonged rainfall deficiency led to severe droughts over the region,featuring abnormally low water levels in rivers,lakes and reservoirs and significant shrinkage of water bodies,and obviously affecting productions and peoples daily life.The results of CI analyses showed that the meteorological drought in spring of 2011 were characterized by greater severity of rainfall deficiency,longer persistency,wider drought range and severe impact on water resource. From the aspect of atmospheric circulation and moisture transportation,a preliminary analyses on the cause of this meteorological drought was carried out.It was indicated that the drought resulted mainly from weak moisture transportation due to the extremely strong southward expanding cold air from the north in winter and spring of 2011 coupled with non active tropical convective systems in the south.Unfavorable moisture transportation conditions made it difficult for warm and cold air flows to meet and produce effective precipitations in the middle and lower basin of the Yangtze River.