Author(s): Yusuke Kume; Makoto Umeda
Linked Author(s):
Keywords: Climate change; River water temperature; Regression analysis
Abstract: Reservoirs play an important role in flood control and water use. In particular, from the viewpoint of water use, they are responsible for the major resources of domestic water in Japan as well as agriculture and industrial waters. On the other hand, various impacts from climate change are becoming apparent in various areas in recent years. Eutrophication phenomenon, especially occurrence of water bloom by cyanobacteria, seems more frequent possibly because of changes in river water discharge and nutrient load affected by alteration of precipitation as well as rising water temperature. Water temperature is generally considered the principal factor to control water quality and ecosystem in natural water bodies. In this study, we investigated the long-term changes in water temperature observed over the past several decades in many dam inflow rivers in all parts of Japan. The observed date of water temperature and air temperature contain seasonal periodic components, which were removed using Fourier series approximation to extract long-term trend components. The relationship between the long-term trend of water temperature change, meteorological data such as air temperature and precipitation, and geographical data with respect to the watershed of the reservoir were then analyzed. The air temperature tended to rise at the most of the reservoirs. On the other hand, a number of inflowing rivers exhibited decreasing trends in water temperature. Besides, the changes of the water temperature and the air temperature were almost uncorrelated. In addition, although some correlation was observed between other meteorological data and geographic data, and water temperature, it was not sufficient to express the change tendency of water temperature.
Year: 2020