Articles | Volume 21, issue 7
Research article
11 Jul 2017
Research article |  | 11 Jul 2017

Temporal variations of groundwater tables and implications for submarine groundwater discharge: a 3-decade case study in central Japan

Bing Zhang, Jing Zhang, and Takafumi Yoshida

Abstract. Fresh submarine groundwater discharge (SGD) is the key pathway of flux and nutrients for the groundwater from land to the ocean. SGD flux is a current issue of discussion and a means to clarify the coastal marine system under climate change. SGD flux accounts for about one-quarter of the river runoff in the Katakai alluvial fan in Uozu, Toyama, Japan, which is an ideal area to study SGD flux considering the need for a rapid response to climate change and the prior research on SGD there. In this paper, the monthly groundwater table's condition over 30 years is analyzed using monthly rainfall, snowfall, and the climate change index. Rainfall has been on an upward trend, but the snowfall has decreased over 40 years. Furthermore, the groundwater table at monitoring wells in the coastal area increased, as a result of the increased rainfall. However, the relationship between snowfall and groundwater is negative. As expected by Darcy's law, SGD flux was controlled by the hydraulic gradient of the coastal groundwater. The estimated historic SGD flux by groundwater table variation shows an upward trend of SGD. Considering the increase in precipitation and the groundwater table, SGD flux may increase under climate change.

Short summary
Since groundwater is the linkage between climate changes and fresh submarine groundwater discharge, the variations of and relationships among monthly groundwater table, rainfall, snowfall, and climate change events from 1985 to 2015 were analyzed by wavelet coherence to discuss the implications for climate changes. The results show the increase in precipitation and the groundwater table, indicating that fresh submarine groundwater discharge flux may increase under climate change.