资源环境科技发展态势分析平台

Recent advancement in climate sciences has discovered two different types of El Nino events, namely the eastern Pacific El Nino (EP-El Nino) and central Pacific El Nino (CP-El Nino). Identifying how watershed responses to different El Nino-Southern Oscillation (ENSO) events, including both El Nino and La Nina conditions, is critical in understanding how the oceanic teleconnections possibly affect local precipitation and streamflow. In this study, 70 watersheds with minimum human impact during the period 1950-2010 in the Southeastern United States (SEUS) were selected to examine whether streamflow exhibits different patterns in EP- and CP-El Nino conditions, and La Nina events. Similar analyses were applied to 187 precipitation stations in SEUS. Analyses reveal that for the peak season of both EP-El Nino and CP-El Nino years, December-January-February (DJF), seasonal average streamflow and precipitation is higher than long-term average. CP-El Nino, however, weakens the wetting effect brought by traditional EP-El Nino, leading to smaller percentage of increases in seasonal precipitation/streamflow for most stations in the SEUS. In the decaying season March-April-May (MAM) of ENSO signals, streamflow for both EP- and CP-El Nino is higher than its corresponding climatology. The increased amplitude is even greater in MAM compared to that of the DJF season. During La Nina events, reduced precipitation and streamflow are observed for large portion of stations in SEUS, especially for the DJF and MAM season. The use of ENSO in water resources management is often limited to boreal winter season for the SEUS, as its signal is well reflected in hydrological responses. This study finds that for the June-July-August (JJA) season followed by the decay of ENSO signals in MAM, there is striking difference in the magnitude of precipitation and streamflow for EP-El Nino and CP-El Nino events.