Long-term hydrological changes of the Seine River flow (France) and their relation to the North Atlantic Oscillation over the period 1950-2008

摘要

The variability of Seine River flow (France) was investigated using daily time series over the period of 1950-2008. The study aimed at characterizing the dominant modes explaining the variability of flow and at investigating their possible link with the North Atlantic Oscillation (NAO) as the dominant climate regime in the region. The Seine River flow was affected by a statistically significant increasing trend across the period. The hydrologic regime of the Seine River was found to be highly variable and seem to occur later in the year, approximately, since the end of the 1980s. Annual minimum, maximum and mean flow time series exhibited an obvious change around 1970. Continuous wavelet transform (CWT) of flow revealed energetic peaks highly localized in time, defining three time periods: before 1970, between 1970 and 1990 and after 1990. Two interannual modes (17 and 5-9 years) occur, respectively, around 1970 and in the early 1990s. The same observations on precipitation CWT ensure a climatic origin to these interannual modes. The annual oscillation was always strongly represented in flow and was affected by an increase in power from 1990 until the end of the time series. Comparison between NAO and annual flow anomalies revealed similar trend behaviour characterized by a change around 1970 towards more positive NAO indices and positive flow anomalies. In addition, CWT of NAO revealed similar modes of variability around 17 and 5-9 years as flow interannual modes. This highlighted a possible link between NAO and hydrometeorological processes in the region. The flow fluctuations (interannual modes and trend) expressing this potential link would explain approximately 23% of total variance of Seine River flow and would even reach 35% of the variance after removal of the annual cyclicity. These results would then emphasize the potential strong control of NAO on the variability of Seine River discharge.