Rainfall and Runoff Observations in the Subtropical Forest of Okinawa Island, Japan

Naoki Kabeya, Akira Shimizu, Takanori Shimizu, Hitoshi Ikuzawa, Takuya Arakaki, Hiroshi Furugen, Yashuhiro Ohnuki, Shiho Asano

Forestry and Forest Products Research Institute, Tsukuba, Japan.
Incorporated Okinawa Prefecture Environment Science Centre, Urazoe, Japan.
Kyushu Research Centre, Forestry and Forest Products Research Institute, Kumamoto, Japan.
Okinawa Prefecture Forest Resource Research Centre, Nago, Japan.

DOI: 10.4236/jwarp.2014.66061                

Abstract

We set up two experimental catchments to provide an improved understanding of hydrological processes in a subtropical forested area in the northern part of Okinawa Island, Japan. We calculated runoff using water level data (recorded by a pressure-type water level gauge installed in a box culvert) and a discharge rating curve (derived from in situ observations). Water balance calculations for 2010 showed that the rainfall, runoff and evapotranspiration losses (= rainfall – runoff) were 3403.6 mm, 2285.7 mm and 1117.4 mm, respectively. This result was in agreement with previous results from other forested experimental catchments in this region. Direct runoff, as a proportion of event total rainfall, can be expressed by the empirical equation (Q_direct = 0.0048, P_event 1.7971, R² = 0.9599). When P_event was 100 mm or less, the ratios of Q_direct to P_event were less than 15% in general. When P_event exceeded 100 mm, the ratios were 20% - 30%.

Keywords

Direct Runoff, Forested Watershed, Okinawa Island, Rainfall-Runoff Observation, Sub-Tropical Forest, Water Balance

Conflicts of Interest

The authors declare no conflicts of interest.

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