PRECIPITATION FACTORS AFFECTING YEAR-TO-YEAR FLUCTUATION IN LOW FLOW OF A FORESTED WATERSHED

Abstract

To provide an assessmento f the effects of the year-to-yearf luctuationi n precipitationa nd forest growth on the low flow of a headwater watershed, 61-year precipitation and discharge data in the Shirasaka Watershed in Japan were analyzed. The minimum flow in winter tended to be greater than that in summer in the 1930s and 1940s, whereas the minimum flow in summer tended to be greater than that in winter from 1950 to 1990. The precipitation factors, which have a reasonable degree of correlation with the annual low flow, were different in summer and in winter. Vegetation growth has occurred for 60 years in this watershed and the differences in trends between low flow and precipitation factors may be due to the effect of vegetation growth.