Hiroki Oue

A stomatal ozone flux-response relationship to assess ozone-induced yield loss of winter wheat in subtropical China.

Stomatal ozone flux and flux-response relationships were derived for winter wheat (Triticum aestivum L.) grown under fully open-air ozone fumigation. A stomatal conductance (g(sto)) model developed for wheat in Europe was re-parameterized. Compared to European model parameterizations, the main changes were that the VPD and radiation response functions were made less and more restrictive, respectively, and that the temperature function was omitted. The re-parameterized g(sto) model performed well with an r(2) value of 0.76. The slope and intercept of the regression between observed and predicted g(sto) were not significantly different from 1 to 0, respectively. An ozone uptake threshold of 12 nmol m(-2) s(-1) was judged most reasonable for the wheat flux-response relationship in subtropical China. Judging from both flux- and concentration-based relationships, the cultivars investigated seem to be more sensitive to ozone than European cultivars. The new flux-response relationship can be applied to ozone risk assessment in subtropical regions.

Comparison of different methods for estimating soil surface evaporation in a bare field

In this paper, three methods for estimating soil evaporation in a bare field were evaluated: evaporation ratio method (k ratio), complementary relationship and bulk equation. Micro-lysimeters were used to measure the actual evaporation for validation of the three methods. For the k ratio method, pan evaporation was used as the reference evaporation instead of the value obtained from the Penman–Monteith equation. This result is important for areas where meteorological data are unavailable. The results showed that, for daytime evaporation, the k ratio and bulk equation produced a good fit with the observation data, while the complementary relationship generated a larger deviation from the measured data. We recommend that the k ratio method and bulk equation could be used to calculate daytime soil evaporation with high accuracy when soil water content and pan evaporation data or meteorological data are available, while the complementary relationship could be used for a rough estimation when pan evaporation is available. All the methods could be applied to calculate cumulative evaporation.

Predicting water surface evaporation in the paddy field by solving energy balance equation beneath the rice canopy

The energy flux on the ground surface depends not only on climatological and biophysical controls in the vegetative canopy, but also on the available energy and energy partitioning beneath the canopy. Quantifying the evaporation and energy partitioning beneath the canopy is very important for improving water and energy utilization, especially in arid areas. In this study, we measured meteorological data, the net radiation and latent heat flux beneath the rice canopy, and then applied the radiation and energy balance equations to get the water surface temperature beneath the rice canopy. To apply the equations, we constructed shortwave and longwave radiation beneath the canopy sub-models and a bulk transfer coefficient sub-model. A plant inclination factor was parameterized with plant area index for the shortwave and longwave radiation sub-models. Bulk transfer coefficient was parameterized by plant area index and soil heat flux was predicted by the force restore model. With calculated water surface temperature and constructed sub-models, we reproduced net radiation and latent heat flux beneath the rice canopy. As a result, the reproduced water surface temperature, net radiation, and latent heat flux beneath the rice canopy were very close to the measured values and no significant differences were found according to 2-tail t test statistical analysis. Therefore, we conclude that these constructed sub-models could successfully represent water surface temperature, net radiation, and latent heat flux beneath the rice canopy.

Evapotranspiration, Photosynthesis and Water Use Efficiency in a Paddy Field (III) -Scaling Impacts of the Change of LAI on Evapotranspiration, Photosynthesis and Water Use Efficiency from leaf to canopy by the Multilayer Model-

前報の多層モデルを用いて葉面積密度の鉛直分布を増減 (葉面積指数LAI＝0～10に相当) させる数値シミュレーションを行い，4つの生育ステージにおいてLAIの違いが個葉の蒸散量と光合成速度に及ぼす影響，そして水田の蒸発散量 (ET)，光合成速度 (CER)，水利用効率(WUEET＝CER⁄ET)に及ぼす影響を検討した．LAIの増加に伴って，ETとCERは漸近的に増加して極大値をとった後減少した．その原因は，LAIの増加に伴って，群落層別の蒸散量と光合成速度が群落上部層で漸近的に増加したが群落中•下部層では逆に減少したためと，株間蒸発量が0に漸近したためである．その結果，WUEETもLAIの増加に伴って最大値に漸近し極大値をとった．朝と夕方や弱光条件では，LAIを増加させると群落中•下部層へ透過する日射量やPARが益々少なくなるため，ET，CERおよびWUEETの極大値が現れやすかった．CERとWUEETについての最適LAIは生育ステージ，時刻，気象条件によって異なり，それぞれ5.0～10.0と5.8～10.0であった．このCERについての最適LAIは，従来のイネ研究で報告された値よりもやや高かった．その主な原因は，本研究では総じて晴天の日を検討対象としたためであると考えられる.

Comparison of the soil physical properties and hydrological processes in two different forest type catchments

Soil physical properties and hydrological processes were analyzed in two experimental catchments with different forest types: one catchment is covered mostly with conifer type trees and the other catchment is covered with conifer and broad leaf trees. To analyze the effects of forest type on soil physical properties, we applied an hourly time step lumped conceptual model, which includes a physically-based infiltration submodel and an evapotranspiration sub-model, to simulate long term discharge. The estimated model parameters and some measured soil characteristics were compared for the two catchments to reveal the differences in soil physical properties. The differences in hydrological processes were compared through observed hydrological factors (rainfall, discharge and meteorological data) between the two catchments.

Local-Level Water Conservation Assessment in the Upstream Watershed Based on Land-Use Scenarios

To assess the effects of differences in land use in a mountainous sub-watershed on water conservation, namely, hydrological services like flood control and groundwater recharge, first, this chapter aims to present a water balance analysis in two sub-watersheds located upstream of the Saba River watershed. Specifically, the Titab and the Busungbiu-Tunju were compared. An annual water balance analysis in the two sub-watersheds in 2013 and 2014 revealed that the ratio of base flow to the total discharge was larger in the Titab, which has a lower areal percentage of clove plantation, a higher percentage of coffee plantation, and a slightly higher percentage of natural forest than the Busungbiu-Tunju. Second, by applying the International Center for Water Hazard and Risk Management/Public Works Research Institute (ICHARM/PWRI) distributed hydrological model, discharges under the present land use and three scenarios of changed land use were predicted. By converting all coffee plantations to clove plantations, base flow decreased, direct runoff increased, and the peak discharge increased. By converting clove plantations at high elevation to coffee plantations, base flow increased, direct runoff decreased, and the peak discharge decreased when compared with the present. In converting all land uses to natural forests, base flow was the largest, direct runoff was the smallest, and the peak discharge was the smallest of all cases. Comparison between the three land uses, coffee plantations, clove plantations, and natural forests, revealed that the clove plantation has the highest possibility of causing a flood disaster, the coffee plantation has a possibility of preventing a flood disaster and increasing groundwater, and the natural forest has the highest possibility of preventing a flood disaster and increasing groundwater.