Youhei Uchida

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.

Reconstruction of the ground surface temperature history from the borehole temperature data in the southeastern part of the Republic of Korea

The changes in the temperature on the Earths surface in the past have penetrated into the subsurface and have been recorded as transient temperature perturbations to the background thermal field. In this study, we reconstruct the ground surface temperature (GST) history of the last 300 years by analysing three borehole temperature profiles in Ulsan, the southeastern part of the Republic of Korea. The borehole temperature profiles show positive temperature anomalies caused by recent warming. The reconstructed GST history showed a cold period in the late 19th century and subsequent warming in the present time. After the cold event, the GST increased by 1.5 K up to 1980. The warming trend from 1900 to 1980 was 2.0 K/century. We compare the GST history with proxy temperature reconstructions obtained by other studies in Northeast Asia. The result suggests spatial variability of the climate in Northeast Asia.