Decadal Variation of the Relationship Between Summer Precipitation along the Huaihe River Valley and SST over the Equatorial Eastern Pacific

The precipitation along the Huaihe River valley plays an important role for the position and the intensity of the rainbelt in eastern China in summer. Based on monthly rainfall data from 160 primary stations in China during 1951—2003 and the NOAA extended reconstruction sea surface temperatures (ERSSTs) data in the same period, the decadal variation of the relationship between summer precipitation along the Huaihe River valley and the SSTs over the equatorial eastern Pacific is studied. Results show that the precipitation is characterized by a remarkable interannual variability, especially by a quasi-biennial oscillation (QBO) during the 1950s to mid-1960s and after the 1980s. Besides the interannual variation, it also contains a distinct abrupt change in the mid-1970s. The precipitation decreases significantly before the abrupt change time while increases after that. The relationship between the summer precipitation and the SSTs in previous winters over the Niño3 regions also differs remarkably with significant negative correlation coefficients before 1974 but with weak and positive values after 1980. Similar patterns can also be found in the composed global SST anomaly (SSTa) fields according to five wettest and driest years in each period along this valley. A 24-year moving window correlation results reveal that the relation in the last two decades is the weakest among the whole research periods. This weakening relationship can also be found in the SSTa fields in previous autumns. Besides this, the relationship between the precipitation and the intensity of the western Pacific subtropical high (WPSH) also possesses a decadal variation with positive coefficients before 1974 but negative after 1980, especially for that of August. During August, the correlation coefficients between the precipitation and the longitudes of the ridge location of the high are -0.56 and 0.03 respectively in the first and second period, while -0.18 and 0.53 respectively for the intensity of the high. That is to say, the rainfall in August is mainly affected by the position of the WPSH in the first period while by its intensity in the second. Above results indicate that the significance of ENSO as a predictor of the summer precipitation along the Huaihe River valley is weakening and the influencing approach of the WPSH is changing. This weakening significance has increased the difficulties of the prediction of China summer rainfall.