Tomokazu Haraguchi

Impact of Climate Change on Irrigation Demand and Crop Growth in a Mediterranean Environment of Turkey

A simulation study was carried out to describe effects of climate change on crop growth and irrigation water demand for a wheat-maize cropping sequence in a Mediterranean environment of Turkey. Climate change scenarios were projected using data of the three general circulation models—GCMs (CGCM2, ECHAM4 and MRI)—for the period of 1990 to 2100 and one regional climate model—RCM—for the period of 2070 to 2079. Potential impacts of climate change based on GCMs data were estimated for the A2 scenario in the Special Report on Emission Scenarios (SRES). The forcing data for the boundary condition of the RCM were given by the MRI model. Daily CGCM2 and RCM data were used for computations of water balance and crop development. Predictions derived from the models about changes in irrigation and crop growth in this study covered the period of 2070 to 2079 relative to the baseline period of 1994 to 2003. The effects of climate change on water demand and on wheat and maize yields were predicted using the detailed crop growth subroutine of the SWAP (Soil-Water-Atmosphere-Plant) model. Precipitation was projected to decrease by about 163, 163 and 105 mm during the period of 1990 to 2100 under the A2 scenario of the CGCM2, ECHAM4 and MRI models, respectively. The CGCM2, ECHAM4 and MRI models projected a temperature rise of 4.3, 5.3 and 3.1 °C, respectively by 2100. An increase in temperature may result in a higher evaporative demand of the atmosphere. However, actual evapotranspiration (ETa) from wheat cropland under a doubling CO2 concentration for the period of 2070 to 2079 was predicted to decrease by about 28 and 8% relative to the baseline period based on the CGCM2 and RCM data, respectively. According to these models, irrigation demand by wheat would be higher for the same period due to a decrease in precipitation. Both ETa and irrigation water for maize cropland were projected to decrease by 24 and 15% according to the CGCM2, and 28 and 22% according to the RCM, respectively. The temperature rise accelerated crop development but shortened the growing period by 24 days for wheat and 9 days for maize according to the CGCM2 data. The shortened growth duration with a higher temperature reduced the biomass accumulation of both crops regardless of CO2-fertilization effect. With the combined effect of CO2-fertilization and increased temperature, the CGCM2 and RCM projections resulted in an increase by 16 and 36% in grain yield of wheat and a decrease by about 25% and an increase by 3% in maize yield, respectively.

Quantification of soil surface evaporation under micro-scale advection in drip-irrigated fields

The objective of this study is to quantify soil surface evaporation under micro-scale advection in drip-irrigated fields. A numerical model for estimating soil surface evaporation under micro-scale advection, assuming drip-irrigated fields, is introduced. Results indicate that the soil surface evaporation changes spatially. Soil surface evaporation at the upwind edge of wet soil portions adjacent to dry soil portions increased abruptly. On the other hand, soil surface evaporation at the upwind edge of dry soil portions adjacent to wet soil portions decreased, and condensation was observed. These phenomena were considered to be due to airflows between differing climates. To verify the accuracy of the model, an experiment using a wind tunnel was conducted. The simulated soil surface evaporation results from the model were consistent with the experimental data. The numerical model introduced here is an effective way to quantify soil surface evaporation under micro-advective conditions.

Impact of aquatic plants on entrainment phenomena based on wind-induced flow in a closed density stratified water area

It has recently been proposed that water purification could be performed using aquatic plants, since they absorb nutrient salts. The behavior of a substance in a closed water area is affected by turbulent flows from wind-induced flow, which is a mechanical disturbance, and convective flow, which is a thermal disturbance. In a closed density stratified water area, wind-induced flow gives rise to the entrainment phenomenon at the density interface. This phenomenon, which is based on mixing between the upper and lower water layers, lowers the density interface and so affects the water quality. We experimentally investigated the effect of aquatic plants on the turbulent flow from a mechanical disturbance in the closed water area. Results indicated that the presence of floating and submerged plants had a significant effect on the scale of the turbulent entrainment, and that the entrainment velocity depended on the overall Richardson number to the power of −3/2.

The impact of floating water plants on wind-induced flow and wind wave in a closed water area

In some closed water bodies, the fluids are generally stratified based on vertical density differences. The causes of density these differences can be categorized as being due to temperature, salt levels, and turbidity. In addition, the dynamics of water environmental substances are induced by wind-induced turbulence, which is based on mechanical disturbances, and convective flow, which is based on thermal disturbances. Wind-induced flow and wind waves are produced when mechanical disturbances act on the water surface. These effects in turn generate a lowering of the density interface and increases in the upper layer density based on mixing between upper- and lower-layer fluids, which is commonly referred to as an entrainment phenomenon. This entrainment phenomenon greatly affects the dynamics of water quality in a closed water body. The production of turbulent energy at the water surface and its transport towards the interface play an important role in the dynamics of water environmental substances. When the surface of a closed water body is partially covered with floating water plants, it is considered that wind waves and wind current based on wind action body affected by the plants to some extent, especially in small reservoirs and creeks, which have less surface area for the wind to acts on. We have previously reported that the value of entrainment velocity decreases as the coverage rate of floating water plants increases. It is considered that the covered water surface cause a reduction in the turbulent energy produced by wind shear. It is therefore important to clarify the effects of floating water plants on the wind-induced flow and wind waves generated by wind shear. Accordingly we experimentally considered the turbulent characteristics of wind-induced flow and wind waves in a closed water body with floating water plants. The results indicate that the energy of wind-induced flow is affected by the existence of floating water plants and that the energy decrease as the covereage rate of floating water plants increases.

Temporal and Spatial Variations in Soil Temperature in Tidal Flat of Ariake Sea, Japan

The tidal variation of the Ariake Bay, which locates in the western part of Japan, is over 6 m. This bay is a closed water area. Tidal flats stretch in the bay, especially in the inner part. Recently water environment has been become worse, specifically, increase in occurrence of hypoxic condition and decrease in fishery. Some researchers think this might occur due to the reclamation of a tidal flat. Tidal flat is a habitation of livings, and has a function to purify water. The purification is decomposition of organic and inorganic matter originated from the land and the sea. Denitrification is caused by bacteria in soil, and the potential depends mainly on soil temperature.

Longwave radiation environment of an irrigation reservoir surrounded by mountains

In areas where irrigation facilities are not available or in mountainous areas, reservoirs are used for paddy rice culture in Japan. Water temperature must be adequately maintained because it affects water quality and has a significant impact on the growth and yield of the rice crop. Stratification of water in a reservoir occurs due to heat storage on the water surface by solar radiation, and destratification results from vertical mixing by wind-induced flow and heat convection. This study used a simple topography model to estimate numerically the spatial distribution of longwave radiation on the water surface of an agriculture reservoir surrounded by mountains. A radiation thermometer was used to estimate global longwave radiation. The spatial and temporal variations of longwave radiation on the water surface were calculated using view factors of objects surrounding the reservoir. The simulation showed that longwave radiation absorbed by the water surface increased with distance from the center of the reservoir. The proposed procedure can be used to estimate the longwave radiation environment and heat balance on a water body such as a reservoir and a stream.

Effect of Floating Vegetation on Wind-Wave in a Closed Water Body

In some closed water body the dynamics of substances in the water are affected by windinduced turbulence based on mechanical disturbances and convective flow based on thermal disturbances. Wind-induced flow and waves are produced when mechanical disturbances act on the water surface. The production of turbulent energy at the water surface and its transit through the density interface play an important role in the dynamics of the water environmental substances contained in the water. When the surface in the closed water body is partially covered with floating vegetation, it is considered that wind waves and wind-induced flow should be to some extent affected by the vegetation, especially in small reservoirs, ponds and creeks that have less surface area upon which the wind can act. Therefore, it is important to clarify the effect of floating vegetation on windinduced flow and wind waves generated by wind shear. We experimentally considered the turbulence characteristics of wind-induced flow and wind waves in the closed water body with floating vegetation using a test tank. This presentation includes a discussion of the impact of floating vegetation on wind-induced flow and wind wave characteristics caused by mechanical disturbance in a closed water body. The result indicate that the energy of wind-induced flow is affected by the existence of floating vegetation and that the wind wave characteristics changed as the floating pattern of the vegetation changed.

Evaluation of water and nutrient deficiency for fertigation using NIR image

For an application of the remote sensing technique on agriculture, an image taken from an artificial satellite is used widely. The image would not be useful in a field-scale precision agriculture due to the limited power of resolution. For the purpose that remote sensing is adopted in a field-scale precision agriculture, the resolution should be increased or an image taken by another technique should be used. In this study, an image of plants was taken by using a digital camera with a band-pass filter. The image was analyzed related with soil moisture and nutrient condition. Broccoli was planted in nine pots different in soil moisture and nutrient condition. An image of plants in a pot was taken by using a digital camera with a band-pass filter (visible range [550, 650, 680, 750nm], NIR range [780, 800nm]) and captured into a personal computer. The digital images were analyzed with computer software to find the reflection characteristics of visible and near infrared rays depending on deficiencies in soil moisture and nutrient. Frequency distribution of brightness was used to evaluate an influence of soil moisture and nutrient deficit from images. The influence due to soil moisture deficit was significantly found in near infrared images (780 and 800 nm) while the difference affected by the nutrient deficit was difficult to be detected with the proposed procedure.

Heat Environment Affected by Different Land Surface Conditions

Study of heat environment and evaporation affected by different surface condition. Observation and simulation of bare, grass and paddy field were performed, which results were compared. The observation was conducted at an experimental farmland. The simulations model used in the study includes numerical model of temperature, wind and humidity distributions in atmospheric boundary layer and soil temperature change. Crop resistance model was adopted to analyze heat energy exchange on surface layer. Using the model, simulations were conducted for 6 fine days in 6 different months using meteorological data measured at other experimental stations. The results show different thermal behavior of the three surface conditions. Temperature order from the highest are bare, grass and paddy; and evaporation order from the highest are paddy, grass and bare.

Effect of Paddy Irrigation Water on Recharging Groundwater

Paddy irrigation water is well known as big contributor of groundwater recharge. During the irrigation season, large amount of water is kept in groundwater and some parts of it flow out to the main river directly or indirectly. The objective of this study is quantifying the effect of the paddy irrigation water on the groundwater recharge, and evaluating of the influence of the land use condition on the groundwater recharge. A comprehensive simulation model of groundwater flow in alluvial plain along Chikugo River, which is located in southwest in Japan, has been established by coupling GIS technique with traditional Finite Differential Model (FDM). In this study, relationships of groundwater level change and land use change were investigated. Using GIS, the fundamental data related to groundwater flow and land use conditions are input at every nodal point as database. A GIS based surface water simulation was carried out and spatial and temporal groundwater infiltration quantity is obtained and provided for groundwater flow simulation. Groundwater flows was calculated by adopting the Successive Over Relaxation (SOR) technique. The simulated result is consistent with the observed data, and the simulation model introduced in this study is fairly satisfactory. The result indicates that the paddy irrigation condition affects on the groundwater recharge. The simulation model introduced here is effective for quantification the groundwater recharge, considering the land use condition.