Canopy rainfall interception and fog capture by pinus pumila regal at Mt. Tateyama in the Northern Japan Alps, Japan

The importance of fog precipitation in the alpine hydrological processes of Pinus pumila canopy was evaluated on Mt. Tateyama, central Japan. We observed rain and fog precipitation, throughfall, and wind direction and velocity at Jodo-daira (36.566°N, 137.606°E, 2840 m a.s.l.) for 3 years. During the snow-free period (August and September), mean monthly rain and fog precipitation was 0.45 mm h ^-1 and 0.14 mm h ^-1, respectively. The mean rainfall interception by P. pumila canopy was about 48%, which is higher than that of other forest canopies at lower altitudes. During rainfall, the dense canopy intercepts rain and the water evaporates from the needle surfaces. On the other hand, the canopy captured fog precipitation even in the absence of rainfall. The amount of throughfall increased with increasing fog deposition. Using δ ¹⁸O and δD analysis, the mean contribution of fog water to the throughfall was estimated at approximately 35%, consistent with the result from direct measurement. These results indicate that P. pumila should have a significant influence on the local hydrological processes of the high mountain ecosystem. The large contribution of fog precipitation can be attributed to the high wind velocity and humidity of the Japan Alps.