Takashi OKUMA
Determination of Hydrological Year and Its Effects on Water Balance Analysis
Minjiao LU
When using hydrological data, it is important to grasp the tendency of the water balance in basin. And a hydrological equation serves as the foundations. By making the period of the hydrological equation into one year, the value of the amount of storage is approximated to 0. However, if it carries out a January 1 start-term and water budget calculation is performed, rainfall and runoff are not in agreement in an area with snow coverage. Then, water budget calculation is performed using a hydrological year.
I investigated the start terms of a hydrological year of fifteen river basins, the Kimotsuki River, the Onga River, the Watari River, the Naka River, the Hii River, the Yura River, the Shingu River, the Kano River, the Kuji River, the Sho River, the Agano River, the Natori River, the Yoneshiro River, the Mu River, and the Teshio River.
As the result, the tendency of the hydrological year in Japan has loosely been classified into four. The start term of the hydrological year of a basin of the Kimotsuki River, the Onga River, the Watari River, the Naka River, and the Shingu River were from December till January. The start term of the hydrological year of a basin of the Kano River, the Kuji River, and the Natori River became the beginning of the month in February. Since the start term of a hydrological year of basins of these two classifications are almost the same as a calendar year, there is little influence of using a hydrologic year. The start term of a hydrological year of a basin of the Hii River, the Yura River, the Sho River, and Agano River became around October and November. The start term of a hydrological year of a basin of the Yoneshiro River, the Mu River, and the Teshio River became around June and July.
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