ANALYSIS OF RIVER WATER TEMPERATURE CHANGES IN JAPAN IN RECENT DECADES

Abstract

 Climate change has been realizing influences on river environments from a number of aspects. This study focuses on changes in river water temperature during recent several decades. Hourly measurement data of water temperature were collected from a database on Internet and one managed by a research foundation. Fourier series were applied to the water temperature data to eliminate seasonal changes. The residual component was used to detect a long term change that may be affected by the climate change. The long term change component of water temperature was slightly correlated with that of air temperature, with a correlation coefficient of about 0.37. Necessary conditions of water temperature measurement regarding duration and frequency were statistically investigated using the actual hourly-measured data. The results suggested that the typical measurement programs of public water environment with an interval of 1 month requires far longer than 20 years of measurement period to detect long term changes with a sufficient precision.