Impact of El Nino / Southern Oscillation on Low-flows in South Georgia, USA

We investigated the impact of El Nino and La Nina climate patterns on the low flows of seven streams in south Georgia. Four stations were located in heavily irrigated areas of southwestern Georgia, whereas three other stations were located in areas of southeastern Georgia with virtually no agriculture. El Nino (La Nina) climate patterns were defined when the 5-month averaged sea surface temperature anomalies recorded by the Japanese Meteorological Association (JMA) are greater than + 0.5 degrees C (lower than -0.5 degrees C) for at least six consecutive months, including the October to December period. With the standard JMA approach, an episode lasts from October to the following September. We also investigated the impacts of a modification to this classical method. In the modified method, an ENSO phase only lasts as long as the temperature conditions (+/- 0.5 degrees C) are met. For the three southeastern stations, low flows recorded during La Nina (El Nino) episodes were usually lower (larger) than the low flows recorded during Neutral episodes from November to April, with differences significant at a level of at least 90 percent from February to April (January to March) only. The four southwestern stations responded similarly, but the significance of the differences was usually lower than for the southeastern stations. The modified classification method tended to give more significant results than the standard method.