Assessing effects of temporal changes in River water temperature on stratification in the Ariake Sea

Abstract

The upward trend of river water temperature due to climate change has recently been confirmed. However, its effects on thermal stratification in coastal waters are not clear. Therefore, targeting the Ariake Sea - a semi-enclosed bay in the island of Kyushu, Japan - we continuously monitored river water temperature during and after August 2015 at the discharge observation stations of Class-A rivers that feed the sea, located in the non-tidal areas of the rivers and closest to the respective river mouths. Numerical simulations were performed on the density stratification in the Ariake Sea using the obtained hourly river water discharge and temperature data, to assess the effects of temporal changes in river water temperature on thermal stratification. It was shown that during a summer flood, river water temperature could influence the reproducibility of the development of thermal stratification depending on the river water temperature used, and the reproducibility of the base water temperature differed during the transition to the mixing period. Effects of river water temperature on the water temperature structure of the sea were indicated.