The Causes of Low Predictive Skills of Precipitation in Flood Season in Northeast China

The real-time forecast accuracies of summer precipitation in Northeast China (NEC) from 1978 to 2018 were significantly low. Moreover, in the recent four years, when the prediction of the overall distribution of summer precipitation anomaly for the whole country was relatively accurate, the prediction of summer precipitation anomaly in NEC was contrary to the actual situation. Therefore, analyzing the cause for the low forecasting accuracy is necessary. In this paper, the forecasting ability of dynamic models and cognitive defects on forecasting summer rainfall in NEC are discussed. Moreover, by systematically reviewing the climatic characteristics, influencing factors, prediction methods of summer drought and flood in NEC, and the real-time forecasting skills, the causes have been obtained as follows: (1) The precipitation in early summer in NEC is mainly affected by the cold vortex activity in NEC, and in midsummer, it is mainly affected by the subtropical high in the West Pacific, the southerly wind in the Northeast, and the circulation pattern in the middle and high latitudes. However, the main dynamic climate models commonly used at home and abroad cannot accurately reflect the key circulation systems associated with precipitation in early summer and midsummer in NEC. (2) The relationship between the summer rainfall in NEC and the global sea surface temperature (SST) is weak and unstable. Especially, the influence of El Niño-Southern Oscillation (ENSO) on summer precipitation in NEC is complicated; the relationship between them varies from decade to decade. (3) The summer rainfall in NEC has remarkable multi-timescale variability (inter-seasonal, inter-annual, and inter-decadal timescales), influenced by different circulation systems, which makes accurately predicting summer precipitation in NEC more difficult. Finally, some scientific problems and possible solutions regarding summer rainfall forecasting in NEC are further discussed, which may be helpful for the future summer rainfall predictions in this area.