Potential Predictors Evaluations And Statistical Prediction Of Summer Rainfall In China

The inter-annual variation of summer rainfall in China is affected by many factors, which is the result of the joint action of the sea-land-atmosphere interaction. In the framework of impacts of sea-land-atmosphere factors on the following summer rainfall, according to the past publications, and on the basis of sea surface temperature (SST), NCEP/NCAR reanalyzed datasets, snow depth in Tibetan Plateau and rainfall datasets provided by 160 observation stations,40 factors possibly affecting East Asia summer monsoon and rainfall in China are reconstructed and evaluated. Firstly, the stability of correlations between prior factors and rainfall in the middle and lower reaches of the Yangtze River basin (YRB) during different period is discussed. Secondly, by the meaning of correlation and historical hindcast, the relationship between the key factors and East Asian summer monsoon (EASM) circulations is analyzed in order to reveal the potential forecast capacity of these factors for the summer precipitation in the YRB. Conclusions are as follows.(1) In the last 60 years, summer rainfall in China appears complex inter-annual variation rule and it also performances obvious regional differences in space. The summer precipitation mainly in space appears'-,+,-'pattern and 'southern flood and northern drought'distribution characteristics.(2) The Western North Pacific Monsoon index (WNPMI) can reflect the flood and drought in the YRB to some extent. The correlation coefficients between factors and monsoon index change as a function of time. Pre-winter Nino3 SST, snow depth over Tibetan Plateau and Northern Hemisphere Subtropical High have better forecast capacity for the WNPMI, but not for rainfall index in the YRB. (3) The relationship between the antecedent factors and summer rainfall in the middle and lower reaches of the YRB is unstable, which presents that their correlation coefficient show a decadal change or positive and negative changes with time. Moreover, the winter important predictors mainly come from the external forcing, such as Nino3 area SST, Kuroshio Current region SST (KCI) and snow depth in Tibetan Plateau. In contrast, spring factors coming from the general circulation show a significant manner such as Arctic Oscillation, Polar vortex, Subtropics high in the Northern Hemisphere, Mascarene high, and Okhotsk high. The correlation between factors above-mentioned and summer precipitation present inter-decadal variation.(4) Among these factors, Kuroshio Current regions SST, snow depth in Tibetan Plateau and surface air temperature near Lake Baikal (SATI) show the significant antecedents for summer rainfall seasonal variability in the YRB by influencing high-low latitude monsoon circulation. In addition, from the field regressed on spring factors such as the polar vortex in the European Atlantic area, the Okhotsk high and the Mascarene high, it also exists the situation in favor of the rainfall over the YRB. Therefore, taking weight and time variation into account, these three winter factors have better forecast capacity for the rainfall seasonal prediction in the YRB after 1970's.