TITLE:
Rainfall and Runoff Observations in the Subtropical Forest of Okinawa Island, Japan
AUTHORS:
Naoki Kabeya, Akira Shimizu, Takanori Shimizu, Hitoshi Ikuzawa, Takuya Arakaki, Hiroshi Furugen, Yashuhiro Ohnuki, Shiho Asano
KEYWORDS:
Direct Runoff, Forested Watershed, Okinawa Island, Rainfall-Runoff Observation, Sub-Tropical Forest, Water Balance
JOURNAL NAME:
Journal of Water Resource and Protection,
Vol.6 No.6,
April
29,
2014
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 (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%.