Interannual-Interdecadal Variations Of Drought In Northeast China

Based on monthly data of precipitation and air temperature at160stations for the period from1951to2012provided by National Climate Center of China, the SPEI index which characterizes the drought was calculated, and the ESMD of this index was performed to investigate the interannual and interdecadal variations of the summer drought in Northeast China. The results show that the summer drought in Northeast China has distinct characteristics of interannual and interdecadal variations. Significant quasi biennial,2yrs, and3yrs oscillations occur in the interannual variations, while quasi17yrs,and22yrs periods occur in the interdecadal variations of the SPEI index in Northeast China. Further studies show that two phases1975-1984and1994-2008are relatively dry, and severe drought occurred during the period1994-2008, while three phases1951-1975,1984-1994and2009-2012are relatively wet. Abrupt test was performed,1994were found to be the change-points of the drought and flood trends for the period1951-2012. The temporal and spatial variance show that the magnitude of drought in June is most obvious. The drought trend show that the increase of drought trend is more obvious in August.Moreover,the atmospheric circulation anomalies which impacts the summer interannual and decadal changes over the Northeast China are analyzed.Results indicate that Asian summer monsoon is closely related with the drought and flood in the northeast of China,when the East Asian monsoon enhanced(weakened),it is relatively wet (drought)in Northeast China. the subtropical high position is northward (southward), it is relatively wet (drought) in Northeast China. On the decadal scale, After1974, the East Asian monsoon significantly weakened,the effect on the drought and flood in the northeast of China weakened. In addition, the relationship between the summer drought in Northeast China and ENSO as well as the Somali cross-equatorial flow was investigated. The EP El Nino (La Nina) is the conventional type of El Nino (La Nina) that has its SST anomaly center located near the South American coast, while CP El Nino (La Nina) is different from the traditional EP El Nino (La Nina), and has its SST anomaly center located close to the date line. As EP El Nino(La Nina) occurs, the summer precipitation in Heilongjiang province of Northeast China is significantly more(less) than normal, however,flood occur in Northeast China.Moreover, it was found that there is a significant negative correlation between the summer drought index SPEI in Northeast China and the intensity of Somali cross-equatorial flow in May. As the Somali cross-equatorial flow in May is stronger, the summer precipitation is significantly less than normal (the drought occurs), and vice versa. Especially,from1996to now, the negative correlation is significant and stable.Therefore, the intensity of the Somali cross-equatorial flow in May can be used as one of predictors for the prediction of drought and flood in Northeast China.