Long time-series variation of crop yield under drought stress and drought vulnerability curves in Songnen Plain, Northeast China

It is of practical significance to reveal the long-term characteristics of drought and its impacts on crop yield in Songnen Plain, an important commodity grain base in Northeast China. This study firstly explored the long timeseries variation of Modified Soil Water Deficit Index (MSWDI) and crop yield at multiple sites in Songnen Plain during 1960-2014 based on numerical simulation with the World Food Studies (WOFOST) model. This study then revealed the mutation of the drought and crop yield with three mutation point test methods, and thereafter explored their relationship between the drought and crop yield with the cross wavelet transform (XWT) and drought vulnerability curve. Results suggested the precipitation was at the lowest level in the 1970 s, which significantly increased in the 1980 s and thereafter exhibited a slow declining trend. Mutation points of drought conditions occurred at multiple stations in 1983, and the crop yields also showed obvious mutation in 1983 or 1984 at two stations. Besides, the drought and crop yield had significant 2-4 year resonance cycles during 1978-1980 at four stations. In particular, periods with high correlation between these two variables were generally years prone to abrupt changes. In addition, determination coefficients of the drought vulnerability curves based on the linear function, cubic curve function and hyperbolic tangent function reached 0.55, 0.65, and 0.64, respectively, suggesting the cubic curve function performed best. The drought vulnerability curve based on the cubic curve function suggested the crop yield loss showed a firstly decreasing and then increasing trend, which may be related to the compensation mechanism of crops. Overall, combination of the mechanistic drought index and crop models provides an effective way to reveal impacts of drought stress on crop yield and offer support information for coping with drought.