Influence of ENSO on precipitation in the East River basin, south China

A majority of the literature analyzing the role of El Nino-Southern Oscillation (ENSO) and other teleconnections has focused on summer precipitation and on global and regional scales. Seasonal precipitation, occurring at local scale (<50,000 km(2); i.e., a size of one grid cell of a typical global climate model), is of considerable importance for flood mitigation, water supply, and water resources management. In view of the relative absence of studies exploring the forces driving local precipitation, the present study examines this precipitation regime (represented by monthly precipitation data for a period of 1956-2005 from 21 gauge stations in the East River basin) as a response to well-known determining factors, i.e., Southern Oscillation Index (SOI), El Nino Modoki index (EMI), and sea surface temperature anomalies (SSTA) of Nino 1 + 2, Nino 3, Nino 4, and Nino 3.4. To achieve the goal of the study, three types of ENSO events were defined: eastern Pacific warming (EPW), central Pacific warming (CPW), and eastern Pacific cooling (EPC). Mann-Whitney U test was applied to assess whether the probabilistic behavior of precipitation in the ENSO period was different from that in the normal period. The Pearson correlation coefficient was calculated to investigate the relations between areal precipitation in the East River basin and the above-mentioned ENSO indices. Results indicated that (1) EPW caused more precipitation in autumn and winter, but less precipitation in summer. EPW even brought about extremely heavy precipitation in summer and winter. (2) CPW caused less precipitation in spring, autumn, and the annual totals. Sometimes, CPW might bring about heavy precipitation. The precipitation pattern in summer in CPW was different from the normal years. (3) EPC caused more precipitation in autumn and less precipitation in spring and winter. The middle East River basin is the region where precipitation has decreased most severely due to EPC. (4) SSTA, SOI, and EMI had significant relations with areal precipitation from January to March. EMI is the only index having significant correlation with precipitation in April.