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...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%.展开更多
The northern area of Okinawa Island is a unique forest area in Japan, with a distinctive ecosystem and subtropical climate. The area is a central region of forestry in Okinawa Prefecture. However, quantitative evaluat...The northern area of Okinawa Island is a unique forest area in Japan, with a distinctive ecosystem and subtropical climate. The area is a central region of forestry in Okinawa Prefecture. However, quantitative evaluation of the effects of the forest environment is inadequate. The authors began meteorological observation of this forested area to address this situation by setting up a weather station in 2009. In this study, we performed research on one of the major factors of the water cycle in forest ecosystems, evapotranspiration. We calculate seasonal changes in potential evapotranspiration through analysis of data from our weather station in 2013, because all measurement elements were assembled. To calculate potential evapotranspiration, we used the Penman equation. We found that the potential evapotranspiration in this forest area was 1170.5 mm in 2013. The mean temperature in 2013 was 20.7°C, yearly average relative humidity was 84.7%, and average wind speed was 1.40 m/s. Regarding the amount of evapotranspiration in the forests of northern Okinawa Island, which has not been previously obtained, it has become possible to calculate the amount of potential evapotranspiration using the Penman equation.展开更多
We develop a new technique to measure the exact upper diameters of trees that is comparatively simple and inexpensive. We can measure the diameters of entire tree trunks efficiently and with high precision. The system...We develop a new technique to measure the exact upper diameters of trees that is comparatively simple and inexpensive. We can measure the diameters of entire tree trunks efficiently and with high precision. The system uses a digital camera with a ~15 - 30× telephoto lens to take a photograph that can be used for measuring the diameter of the upper part of a comparatively slender tree trunk. Since this method requires a measuring distance and the height of the target point in the image, a range finder capable of measuring angles was combined with the main digiscoping system. A range finder sensor uses a laser and makes a 360 degree angle of observation possible. The diameter of a target position of the objective tree can be obtained by measuring the digital image using image editing software and calculations from spreadsheet software. We focus on the Japanese cedar species in the southwestern part of Japan. Photographic measurements were obtained prior to thinning. The estimates that we obtained largely agree with the true measurements of all trees. With regard to the estimated accuracy of all measured trees, the maximum error ratio was 7.0% (1.45 cm), with a ~2% - 4% error for most of the estimated results. Although the absolute value of the estimation error was 1.87 cm (5.3%) at the maximum (9.87 m in height and 35.5 cm in diameter), an estimation accuracy of <1 cm was reproduced in almost all measurements except for the extreme hypertrophy portion by butt swelling.展开更多
文摘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%.
文摘The northern area of Okinawa Island is a unique forest area in Japan, with a distinctive ecosystem and subtropical climate. The area is a central region of forestry in Okinawa Prefecture. However, quantitative evaluation of the effects of the forest environment is inadequate. The authors began meteorological observation of this forested area to address this situation by setting up a weather station in 2009. In this study, we performed research on one of the major factors of the water cycle in forest ecosystems, evapotranspiration. We calculate seasonal changes in potential evapotranspiration through analysis of data from our weather station in 2013, because all measurement elements were assembled. To calculate potential evapotranspiration, we used the Penman equation. We found that the potential evapotranspiration in this forest area was 1170.5 mm in 2013. The mean temperature in 2013 was 20.7°C, yearly average relative humidity was 84.7%, and average wind speed was 1.40 m/s. Regarding the amount of evapotranspiration in the forests of northern Okinawa Island, which has not been previously obtained, it has become possible to calculate the amount of potential evapotranspiration using the Penman equation.
文摘We develop a new technique to measure the exact upper diameters of trees that is comparatively simple and inexpensive. We can measure the diameters of entire tree trunks efficiently and with high precision. The system uses a digital camera with a ~15 - 30× telephoto lens to take a photograph that can be used for measuring the diameter of the upper part of a comparatively slender tree trunk. Since this method requires a measuring distance and the height of the target point in the image, a range finder capable of measuring angles was combined with the main digiscoping system. A range finder sensor uses a laser and makes a 360 degree angle of observation possible. The diameter of a target position of the objective tree can be obtained by measuring the digital image using image editing software and calculations from spreadsheet software. We focus on the Japanese cedar species in the southwestern part of Japan. Photographic measurements were obtained prior to thinning. The estimates that we obtained largely agree with the true measurements of all trees. With regard to the estimated accuracy of all measured trees, the maximum error ratio was 7.0% (1.45 cm), with a ~2% - 4% error for most of the estimated results. Although the absolute value of the estimation error was 1.87 cm (5.3%) at the maximum (9.87 m in height and 35.5 cm in diameter), an estimation accuracy of <1 cm was reproduced in almost all measurements except for the extreme hypertrophy portion by butt swelling.
