Interference of natural and anthropogenic forcings on variations in continental freshwater discharge from the Red River (Vietnam) to sea

Continental freshwater discharge is vital to global human development. Intensive studies have been conducted on changes of river discharge around the world (Dai et al., 2009; Milliman and Farnsworth, 2011). However, little work has been carried out on the daily continental freshwater discharge of the Red River in response to influence of the natural and anthropogenic forcings. This paper presents results of change analysis of daily continental freshwater discharge over the period 1956-2009 in the Red River. The wavelet analysis results showed observable periodicities in the continental freshwater discharge series with 4-6 months, 8-12 months, 1.5-2 years, and 4-7 years (48-80 months), respectively. The results from Mann-Kendall test indicated insignificant trends in annual continental freshwater discharge during the study period, but there is clearly decrease in annual suspended particulate matter of the Red River. It is shown that the continental freshwater discharge from the Red River was dominated by precipitation over the catchments. Moreover, changes in the continental freshwater discharge are closely related to SASM (the South Asia Summer Monsoon) and ENSO (EI Niño Southern Oscillation). Variations in daily discharge are lagged behind SASM 13-29 days. It revealed that El Niño and La Niña events are likely to induce extreme low and extreme high continental freshwater discharge from the Red River into the Tokin Gulf, respectively. Meanwhile, continental freshwater discharge from the Red River into the Tonkin Gulf experienced abrupt changes with present characteristics as 'no flood in the flood season, no drought in the drought season' due to water regulation induced by dam.