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 (Qdirect = 0.0048, Pevent 1.7971, R2 = 0.9599). When Pevent was 100 mm or less, the ratios of Qdirect to Pevent were less than 15% in general. When Pevent exceeded 100 mm, the ratios were 20% - 30%.
 Wohl, E., Barros, A., Brunsell, N., Chappell, N.A., Coe, M., Giambelluca, T., Goldsmith, S., Harmon, R., Hendrickx, J., Juvik, J., McDonnell, J.J. and Ogden, F. (2012) The Hydrology of the Humid Tropics. Nature Climate Change, 2, 655-662.
 Gossling, S. (2001) The Consequences of Tourism for Sustainable Water Use on a Tropical Island: Zanzibar, Tanzania. Journal of Environmental Management, 61, 179-191. http://dx.doi.org/10.1006/jema.2000.0403
 Kakazu, H. (2011) Sustainable Island Tourism: The Case of Okinawa. In: Carlsen, J. and Butler, R., Eds., Island Tourism: Sustainable Perspectives, CAB International, Wallingford, 171-185.
 Ishijima, S., Kimura, R., Yokoyama, T., Shimose, R. and Yoshinaga, A. (2000) Observations of the Surface Temperature of the Northern Region of the Okinawa Island with a Preliminary Analysis of Therein Water Balance. Bulletin of the Faculty of Science, University of the Ryukyus, 70, 49-62.
 Sueyoshi, M., Goto, H., Sato, H., Hattori, T., Kotaka, N. and Saito, K. (2009) Clusiidae (Diptera) from Log Emergence Traps in the Yambaru, a Subtropical Forest of Japan. Entomological Science, 12, 98-106.
 Kanna, K., Arakaki, T. and Kinjyo, M. (2001) Effect of Erosion Control Work on Forest Watershed Conservation—A Case Study of Hydrological Observation at Hentona of Kunigami Village. Bulletin of Okinawa Forest Research Institute, 44, 1-14.
 Kabeya, N., Shimizu, A., Shimizu, T., Arakaki, T., Furugen, H., Ikuzawa, H. and Ohnuki, Y. Canopy Interception Bservations in the Northern Forest of Okinawa Island. Kyushu Journal of Forest Research, in Press.
 Kabeya, N., Shimizu, A., Shimizu, T., Asano, S., Ikuzawa, H., Imada, M., Higa, M. and Fugugen, H. (2011) Rainfall and Runoff Observations in Forested Watersheds Located in the Sub-Tropic Small Island (II). Kyushu Journal of Forest Research, 64, 105-107.
 Shimizu, A., Miyabuchi, Y., Shimizu, T., Ogawa, Y., Daimaru, H., Sato, T. and Takeshita, M. (2008) Statistical Report of Hydrological Observations at the Sarukawa Experimental Watershed (January 1987 to December 2000). Bulletin of Forestry and Forest Products Research Institute, 406, 13-65.
 Asano, S., Shimizu, A., Kabeya, N., Hagino, H. and Tamai, K. (2011) Statistical Report of Hydrological Observations at the Sarukawa Experimental Watershed (January, 2001 to December, 2005). Bulletin of Forestry and Forest Products Research Institute, 407, 49-71.