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Volume 63, Issue 1
Displaying 1-5 of 5 articles from this issue
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Full Papers
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Tetsuo KOBAYASHI, Jun'ichi TESHIMA, Risa IWANAGA, Daichi IKEGAMI, Dais ...2007 Volume 63 Issue 1 Pages 1-10
Published: 2007
Released on J-STAGE: June 13, 2007
JOURNAL FREE ACCESSThe bucket with a bottom hole (BBH) model of soil hydrology was improved to incorporate bioprocesses such as surface rainfall interception and macropore flow into it by introducing three model parameters or two composite parameters. The improved model (BBH-B model) was applied to the estimation of evapotranspiration (ET) from a cornfield in the upper Yellow River. The results obtained are summarized as follows.
(a) Estimates of the cumulative ET during periods of about one month were made using the BBH-B model with fair accuracy if the model parameters could be evaluated appropriately.
(b) ET had a large spatial variation within the cornfield.
(c) The major zone of water use by corn moved downward through the soil as the growing season progressed. The ratio of root water uptake in depths between 40 cm and 100 cm to ET increased from about one-forth in June, when LAI increased quickly, to about one-half in September, when the corn maturred.
(d) The surface conditions, such as the fraction of crop cover, exerted a large influence on the partition of rainwater at the surface of the cornfield.View full abstractDownload PDF (899K) -
Toshichika IIZUMI, Yousay HAYASHI, Fujio KIMURA2007 Volume 63 Issue 1 Pages 11-23
Published: 2007
Released on J-STAGE: June 13, 2007
JOURNAL FREE ACCESSA cool summer seriously damages rice production in Japan under the present climate. On the other hand, an extremely hot summer may reduce production because of heat stress during the flowering period in a post-global warming climate. Reliable impact projections are required to grasp the hazards of production variability. However, accuracy limitations of the General Circulation Model (GCM) products obstruct impact projections in a particularly extreme year. A new dynamic downscaling method is suggested by the current study, which contributes to estimating a higher-resolution climate from GCM products while reducing the GCM bias. The bias means the difference between the simulated value and observations, and is the most serious factor in decreasing the reliability of impact projections. This study aims to show the difference in (1) the region-scale climate change and (2) the influence on rice production between a cool summer year and a hot summer year after global warming. A Regional Climate Model (RCM) downscales the change in climate over Japan based on GCM products under the Special Report for Emission Scenario-A2 scenario. Simulated changes in daily maximum/minimum temperatures, daily total solar radiation and monthly total precipitation vary depending on the target month and the area. Crop model simulations show that climate changes reduce the damage caused by a cool summer throughout Japan. On the other hand, climate changes enhance the damage caused by heat stress in central to southwestern Japan, but the damage is not found in northern Japan even in a hot summer year. As the result of global warming, the damage to yield from a cool summer is mitigated; however, damage from heat stress is enlarged in a post-global warming climate.View full abstractDownload PDF (2220K)
Short Papers
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Ryoji SAMESHIMA, Tomoyoshi HIROTA, Takahiro HAMASAKI2007 Volume 63 Issue 1 Pages 25-32
Published: 2007
Released on J-STAGE: June 13, 2007
JOURNAL FREE ACCESSStatistically expected early first-frost days with return periods from 2 to 30 y (EFFDk, where k represents the return period) were calculated by fitting frost records obtained at weather stations to the Weibull distribution function. To create 1 km2 mesh maps of EFFDk, a method to estimate EFFDk was developed by relating k to the normals of daily minimum air temperature (Tm).
An equation to calculate the probability of occurrence of the first frost before day x ((P (X ≤ x)) from Tm was derived. Risk of early first-frost damage to soybeans was defined as (P (X ≤ maturity day). Day of maturity was estimated with existing soybean developmental models, and risk maps of first-frost damage to soybeans were created.View full abstractDownload PDF (1160K)
Full Papers (in Japanese)
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Yasutomo HOSHIKA, Tomohiro HAJIMA, Yo SHIMIZU, Kenji OMASA2007 Volume 63 Issue 1 Pages 33-39
Published: 2007
Released on J-STAGE: June 13, 2007
JOURNAL FREE ACCESSThe global warming caused by greenhouse gases such as carbon dioxide is one of the major environmental issues. Because forest vegetation absorbs carbon dioxide from the atmosphere through the process of photosynthesis, the assessment of carbon uptakes by forest vegetation is important for controlling the global warming. The net primary productivity (NPP) is one of indices for the assessment. The estimation of NPP under future climate conditions will change when the assumption of vegetation distributions are different. Therefore, in this study, we examined how the estimated NPP of forest vegetation in Japan is affected by the difference in vegetation distribution, using a modified model of BIOME3 (Ishigami et al., 2002).
The process-based model, BIOME3 (Haxeltine and Prentice, 1996) enabled us to simulate NPP and the potential natural vegetation, i.e., the vegetation distribution that is in equilibrium with a given climate condition. By this model, the estimated total annual NPP of the current forest vegetation, 0.15 Pg C y-1, was about 11% lower than NPP of potential natural vegetation. This difference is caused by the difference in vegetation distribution. It follows that the effect of the difference in vegetation distribution on NPP needs to be considered for the future projection. To verify the model validity, we also compared the calculated NPP with the Chikugo model and the observation.View full abstractDownload PDF (1085K) -
Masana YOKOYA, Daisuke KOMORI, Pedram ATTAROD, Masatoshi AOKI, Katsuto ...2007 Volume 63 Issue 1 Pages 41-49
Published: 2007
Released on J-STAGE: June 13, 2007
JOURNAL FREE ACCESSRecently, cultivation of cabbages by hill tribes has been rapidly expanding in the mountainous regions of northern Thailand. This leads to a, fear of water shortage caused by hill farming and irrigation. To estimate water consumption, predicting the amount of evapotranspiration (ET) that occurs in irrigated cabbage fields is required.
In the present research, portable chambers were used to measure the actual ET occurring in irrigated cabbage fields. Since the measurement period was restricted in Thailand, measurements were also carried out in cabbage fields in Japan.
The results showed that daily ET was the same despite differences in the sizes of cabbage plants with sufficient soil moisture. Furthermore, strong correlations existed between ET, solar radiation (Rs) and vapor pressure deficit (VPD). This tendency was the same in Thailand and Japan. The authors then derived an empirical equation using Rs and VPD data measured in both Thailand and Japan to estimate ET from irrigated cabbage fields.
The empirical equation was validated using the data measured in Thailand and Japan, and it was determined that the root mean square error (RMSE) was 0.6 mm/day-1 for a daily scale.
Our results also indicated that ET decreased sharply with soil water content (SWC) less than 30%. However, the field survey determined that cabbage fields are regularly irrigated with SWC higher than 30% in these regions.
Therefore, it is possible to estimate ET from irrigated cabbage fields using the proposed equation.View full abstractDownload PDF (1481K)
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