Author(s): Huaxia Yao; Michio Hashino; Tohru Kanda
Linked Author(s): T. Kanda, Michio Hashino
Keywords: Nnual water budget; Water resource reduction; Forest foliage; Rainfall; Temperature; Evapotranspiration; Shikoku
Abstract: Annual water budgets are analyzed for two mountainous and forested basins in the Shikoku Island of Japan, and their changing trends within 36 years are explained. Similar and notable trends are found: small increase in rainfall, but small decrease in runoff and large increase in evapotranspiration. The remarkably increased evapotranspiration is found to be mainly caused by extraordinary forest plantation and growth, not by rainfall change, temperature change or domestic water usage. Mean annual runoff within 1984-1993 decreased by 68 mm at the Nagayasuguchi Dam basin, compared with the runoff in 1957-1964, although the rainfall increased by 165 mm. That is because the evapotranspiration increased remarkably by 308 mm due to doubled forest foliage. In another basin of the Hiji River, annual runoff within 1960-1969 decreased by 140 mm while the rainfall increased by34 mm, because the evapotranspiration increased by 173 mm due to enhanced forest foliage. These results imply that extraordinarily enhanced forest may bring about reduction in water resource in rivers, although it has many beneficial functions in flood control, sediment prevention and environmental improvement.
Year: 2001