Yasuo Sakura

Disturbances of temperature-depth profiles due to surface climate change and subsurface water flow: 1. An effect of linear increase in surface temperature caused by global warming and urbanization in the Tokyo Metropolitan Area, Japan

A series of type curves is presented for evaluating vertical groundwater fluxes under the condition of a linear increase in surface temperature. The depths of minimum groundwater temperature in the temperature-depth profiles indicate the magnitude of the downward groundwater flux. The type curve method has been applied to the subsurface thermal regime observed in Tokyo metropolitan area, Japan, to estimate the vertical groundwater fluxes under the condition of surface warming caused by global warming and urbanization. The groundwater fluxes obtained from the type curves and the depths of minimum groundwater temperature agree well with the values obtained from the other studies in the Tokyo metropolitan area. The inversion due to the surface warming could be a good tracer to detect the groundwater flow system.

Prediction of changes in soil moisture associated with climatic changes and their implications for vegetation changes: Waves model simulation on Taihang Mountain, China

The WAVES model was used to simulate the effect of global warming on soil moisture on the semi-arid Taihang Mountain in China. Parameters of the WAVES model were first adjusted according to soil moisture data from a field global warming experiment. Then, the reliability of WAVES in predicting soil moisture changes induced by climatic change was confirmed by comparing the simulated and observed soil moisture values under different climatic conditions and plant growth rates of another field treatment. Next, 10 climate change scenarios incorporating increases in temperature and changes in precipitation were designed. When a simulation was conducted using the leaf area index (LAI) growth pattern from a field experiment under the present climatic conditions, the results suggested that the combination of temperature increase and precipitation decrease would greatly decrease soil water content throughout the entire simulation period. On the other hand, only when precipitation increased by 20% and temperatureincreased by 2 °C, the effect of precipitation increase on soil moisture was obviously positive. Although soil moisture conditions in the T2P1 (temperature increase by 2 °C and precipitation increase by 10%) and T4P2 (temperature increase by 4 °C and precipitation increase by 20%) scenarios were slightly better during the rainy season and notmuch changed before the rainy season, the positive effect of 10%precipitation increase on soil moisture was totally offset by moisture decrease caused bya 4 °C temperature increase in the T4P1 scenario. At the same time, the trends of soil-moisture change were highly coincident with predicted changes in productivity. Finally, the predicted LAI values from other studies were combined with the climatic change scenarios and used in the simulation. The results showed that changes in LAI alleviated, at least to some extent, the effects of temperature and precipitation changes on soil moisture.

Effects of urbanization and groundwater flow on subsurface temperature in three megacities in Japan

Subsurface temperatures were used to evaluate the effects of both urbanization and groundwater flow in three megacities in Japan. The magnitude of the heat island and time of the start of urbanization are preserved in subsurface temperature, and these signatures are clarified by meteorological data from these three cities. Heat conduction–convection analyses of subsurface temperature under the conditions of surface warming show that the ranges of the subsurface temperature indicate the magnitude of the regional groundwater flow in these three megacities in Japan.

Distribution of subsurface temperature in the Kanto Plain, Japan; estimation of regional groundwater flow system and surface warming

Abstract Temperature-depth profiles and hydraulic heads were measured on 88 observation wells in the Kanto Plain. Subsurface temperature distribution in the Kanto Plain is assumed that it is strongly affected by heat advection due to groundwater flow. The high temperature area is located in lowlands around the Kinu River, the Tone River and the central part of the plain. On the other hand, the low temperature area is distributed in highlands such as hills and uplands located in the surroundings of the plain. Considering the observed distribution of subsurface temperatures and hydraulic heads, we estimated that there are two local groundwater flow systems which discharge to the Tone River and the Kinu River, and one regional groundwater flow system, in which the water is recharged in the surroundings of the plain and is discharges to the central part of the plain. Moreover, it was observed that 30 temperature-depth profiles have minimum temperature. The distribution of the depth of minimum temperature in the temperature-depth profile has tendency that the depth in the recharge area is deeper than that in the discharge area. This tendency indicates the existence of the regional groundwater flow system in the Kanto Plain.

Shallow subsurface thermal regimes in major plains in Japan with reference to recent surface warming

Abstract It is generally recognized that the temperature profile in a borehole is affected by both groundwater flow and past climatic change. Solid earth scientists seek to remove such effects from a temperature profile for the corrections of terrestrial heat flow values. It has also been well recognized by hydrogeologists that the distribution of subsurface temperature is affected by groundwater flow and that those temperature data can be used to evaluate the direction and velocity of groundwater flow. There are studies dealing with the effect of surface temperature change on the subsurface thermal regime in the solid geophysical literature, and there are studies on the effect of groundwater flow on subsurface temperatures in the hydrogeological literature. However, there are few studies including both effects. This paper intends to provide some evidence of interactions between the two competing effects that we can see at depths about 30–300 m in Japanese basin or plains. We have compiled shallow subsurface temperature–depth profiles at depths about 30–300 m in Japanese basins and plains. Number of thermal data set is 15 areas from Hokkaido to Kyushu at present, and we can classify thermal data sets into four categories depending on the thermal regime. This paper, moreover, describes details of the subsurface thermal regimes in the Yamagata Basin and the Nobi Plain. Thermal regime in the Yamagata Basin was calculated by two-dimensional analytical solution and estimated the effect of regional groundwater flow. Result of three-dimensional heat transport simulation in the Nobi Plain shows that there are two effects of regional groundwater flow and surface temperature warming owing to urbanization on subsurface thermal regime.

Assessment of urban groundwater heat contaminant in Jakarta, Indonesia

Urbanization has become one of the domain processes for city development in Indonesia. The results of the extremely high densities of fast growing population have led to negative subsurface environmental impact. Jakarta, as one of the rapidly developed and urbanized cities in Southeast Asia, has become one of the interesting urbanization city to analyze its effects. In Jakarta, the use of groundwater has greatly accelerated conforming to the rise in its population and the development of the industrial sector, which consume a relatively large amount of water. The increase of groundwater exploitation in Jakarta city has already caused a negative impact on these resources. Therefore, an assessment of groundwater trends in the urban area, including their hazard and risk management, is a necessary action. This paper describes the assessment of urban groundwater loading caused by human concentration in Jakarta city. Subsurface heat contamination under the condition of surface warming shows significant effects of urban groundwater loading during the past century in Jakarta city.

Groundwater flow and subsurface thermal regime

It is generally recognized that the temperature profile in a borehole is influenced by both groundwater flow and past climatic change. Geophysicists seek to remove such effects from a temperature profile for the corrections of heat flow values. It is also well known by hydrogeologists that the distribution of subsurface temperature is affected by groundwater flow and that temperature data can be used to estimate the direction and velocity of groundwater flow. Until present, there are few studies dealing simultaneously with both effects. This workshop provides a review of the literature dealing with the effects of groundwater flow and past climatic change on the subsurface thermal regime. Then, temperature profiles and the distribution of temperature inversions in Japan, Germany and China are analyzed and presented as examples showing both effects as well as the effects of surface warming owing to urbanization.

Groundwater Flow Systems in Yoro River Basin Estimated from Stable Isotope, Subsurface Temperatures and MODFLOW

Yoro river basin is located at the center of Boso peninsula, Chiba prefecture. Its area is 250 Km2, with maximum width of about 10 Km, length of 40 Km, then a relative height of 360 m and, a slope of 0.5 degree dipping northwards to the Tokyo bay. The topography of the area has been classified from South to North into three groups: Kazusa hills, Shimosa upland and alluvial plain. These geomorphobgical units belong respectively to the geological features of Kazusa group, Shimosa group and alluvium. From oxygen isotope analysis and subsurface temperature distribution, three groundwater flow systems of almost equivalent concentration of oxygen isotope are distinguished: the regional, intermediate and local. Natural recharge areas consist of zones of low subsurface temperature and, discharge areas of zones of high temperature. The regional and intermediate flow systems are recharged upstream of Yoro river basin at Kazuasa hills and, discharged respectively near the seashore and the middle of the basin through the kasamori formation (top layer of Kazusa group composed of muddy strata). The flow of discharging groundwater is at the origin of high subsurface temperature areas. The local flow system recharges at the Shimosa upland (midstream) and discharges at the alluvial plain (downstream river basin). These flow systems have been confirmed by a 2-D steady state numerical simulation using the MODFLOW program on a cross-section along the main groundwater flow direction.

The Lysimeter Experiments and Numerical Simulations on Behavior of DNAPL in the Unsaturated Zone

Lysimeter experiments were conducted to study the behavior of NAPLs in unsaturated zone by simulated rain. TCE and Bromide were used in the experiments to trace the behavior of DNAPL and water respectively. Soil properties such as porosity and hydraulic conductivity were measured at nine depths. Soil water potential was measured with tensiometers and soil water contents were checked by a nuclear soil water meter and TDR. The water was sprinkled from the top of the lysimeter during the ten experiments. At the beginning of the first experiment, pure TCE and bromide-dated water were put at the surface of lysimeter. Soil water and soil gas in the unsaturated zone were sampled and analyzed during and after rain events. Soil water content increased as lapsed time from 20 % to 30 % approximately. By comparing the velocity of infiltrating water with that of TCE, it was found that pure TCE liquid did not always move straight downward immediately and TCE gas moved more quickly than water in the unsaturated zone where TCE gas migration was important. Using experimental results, some numerical simulations were carried out to reveal the behavior of TCE in both gaseous phase and dissolution phase. Compared the vertical profile of TCE concentration experimented and that of calculated, some parameters such as diffusion coefficient, partition coefficient and decay coefficient have been derived.