Abstract:

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.