Seasonal Drought Characteristics And Its Interdecadal Variation Factors In Northeast China From 1961 To 2012

The decline in ecosystem productivity caused by drought has become a global observation fact.Under the future ecological environment background,drought will become more and more serious.With global warming,temperature appears an upward trend and Precipitation continue to reduce and drought frequency goes up in Northeast China.It's satisfied with SPEI that monitor and estimate through drought period in Northeast China.According to meteorological data monthly in 1961-2012 years in Northeast C hina,we investigate SPEI time distribution and impact factors of drought process at seasonal time scales in Northeast C hina by EOF.And investiga te the seasonal features of interdecadal variation of drought between 1961-2012 years in Northeast C hina by climate statistics like M-K test,low pass filtering,etc.And study atmospheric circulation characteristics and the correlation between SST and interdecadal transition in autumn from 1961 to 2012 by climate statistics like synthesis analysis,correlation analysis,etc.The main conclusions:(1)The results show that the first EOF modes of SPEI in each season reflects same anomaly in whole area and the second one reflects opposite anomalies in the south and north which borders from 47°N to 48°N in Northeast China.Under the first EOF mode which is the mode of same anomaly in whole area,SPEI in spring represented as low volatility before 1988,more drought period during 1988 to 2000,and after 2000 have a uptrend that turn drought to water-logging period.SPEI in summer has interannual-interdecadal fluctuation,most are drought period before 1974,during 1974-1980 exist water-logging period momentarily,1984 to 1996 are water-logging period basicly,turned in 2000 become drought tendency.SPEI in autumn have interdecadal characteristics obviously,which divided into water-logging period in 1961-1974 and 1982-1994,drought period in 1974-1982 and 1994-2012 roughly.SPEI in winter present as drought period completely before 1986,and has relieved after 1986,even appear water-logging trend,exist drought around 2000 yet.(2)From Interdecadal variations characteristics,it's unnoticeable with the time series of SPEI in spring.Drought years are 10(1963,1969,1974,1980,1983,1992,1993,2003,2005,2011).Removing the high frequency by filtering,it can be divided in 3 interdecadal variations period: Water-logging from 1965 to 1979 and 1998 to 2008,drought from 1980 to 1997.It's unnoticeable with the time series of SPEI in summer,drought years are 8(1965,1970,1982,1987,1999,2000,2001,2003)It can be divided in 3 interdecadal variations period: Water-logging from 1973 to 2004,drought from 1965 to 1972 and 1996 to 2005.It's significant with the time series of SPEI in autumn.Drought years are 11(1968,1976,1979,1980,1999,2001,2002,2005,2006,2007,2008).Approximately before 1973 is water-logging period,from 1973 to 1981 is drought period;and from 1982 to 1994 is the second water-logging period,after 1995 is the second drought period.It's unnoticeable with the time series of SPEI in winter.Drought years are 11(1962,1967,1970,1971,1978,1983,1986,1990,2001,2005,2011).It can be divided in 4 interdecadal variat ions period: Water-logging from 1965 to 1981 and 1991 to 2001,drought from 1982 to 1990 and 2002 to 2008.Between 1972-1982 and 1990-2000,there are two interdecadal transitions of SPEI in each season in features of interdecadal variation,especially in autumn.(3)Due to the outstanding characteristics that SPEI interdecadal variations in autumn,there is a certain correlation with the atmospheric circulation and SST variability.In autumn,according to 500 h Pa Geo-potential Height field,the whole layer Vapor flux D-value field,and 700 h Pa vertical velocity D-value field,compared with water-logging period,Northeast China under the control of positive D-value Geo-potential Height field,which make advantageous rise temperature.The area is under the control of passive D-value area,and the northern edge is in the region of vapor positive D-value that illustrates vapor outflow and count against precipitation.Northeast C hina is in the area of descending motion D-value that adverse to precipitation.(4)On the basis of SST D-value field in summer and autumn,they both exist-IPO likeness SST D-value condition in the Pacific Ocean and +AMO likeness in the North Atlantic.Meanwhile,in Northeast C hina,IPO,AMO in summer and autumn have the same interdecadal transition with SPEI in autumn during 1982 to 2012,coefficient of association with Autumn SPEI:0.30(Summer IPO),0.27(Autumn IPO),-0,26(Summer AMO),-0.26(Autumn AMO).The turning point is in the mid and late 1990 s which have concerned correlations between IPO,AMO and SPEI.Compared with water-logging period,during drought period,-IPO SST status in Pacific Ocean can lead to positive D-value in North Pacific which means warmer SST,rise 500 h Pa Geo-potential Height field over it,and +AMO which implies warmer in North Atlantic,act on 500 h Pa Geo-potential Height field that may produce an effect on the area of Northeast China by teleconnection.