Disturbances of Temperature-Depth Profiles by Surface Warming and Groundwater Flow Convection in Kumamoto Plain, Japan

Linyao Dong,Congsheng Fu,Jigen Liu,Yifeng Wang

doi:10.1155/2018/8451276

Abstract

Subsurface temperatures depend on climate and groundwater flow. A lack of observations of subsurface temperature collected over decades limits interpretation of the combined influences of surface warming and groundwater flow on subsurface thermal regimes. Subsurface temperature-depth profile data acquired for Kumamoto Plain, Japan, between 1987 and 2012 were collected and analyzed to elucidate regional groundwater and heat flows. The observed and simulated temperature-depth profiles showed the following: subsurface water flows from northeast to southwest in the study area; the combined influence of surface warming and water flow perturbation produces different temporal changes in thermal profiles in recharge, intermediate, and discharge areas; and aquifer thermal properties contribute more than hydraulic parameters to the perturbation of temperature-depth profiles. Spatial and temporal evolution features of subsurface thermal regimes may be utilized to investigate the influence of surface warming events on subsurface water and heat flows at the basin scale.

Highlights

Temperature-depth profiles may be disturbed by both surface warming events and subsurface water flow [1, 2]
This study extends analyses of observed subsurface temperatures in different decades to theoretical analyses using numerical modeling and investigates temporal changes in subsurface temperature under the combined influence of surface warming and regional groundwater flow
Convection of water flux produces a high subsurface temperature at the same depth in the discharge area. These features are used to depict groundwater flow in Kumamoto Plain, where 28 temperature-depth profiles were collected in July 2012 to detect local subsurface water flow features

Summary

Introduction

Temperature-depth profiles may be disturbed by both surface warming events and subsurface water flow [1, 2]. Stallman [8] first presented the basic governing equations of simultaneous transfer of heat and water in a porous medium This general equation was solved analytically [1, 9,10,11] and numerically [12, 13] to interpret groundwater flow patterns from the observed temperature-depth profiles. This study extends analyses of observed subsurface temperatures in different decades to theoretical analyses using numerical modeling and investigates temporal changes in subsurface temperature under the combined influence of surface warming and regional groundwater flow. The main objectives were to evaluate changes in groundwater flow systems between 1987 and 2012 based on repeated measurements of subsurface temperature, to elucidate the temporal and spatial evolution of the subsurface temperature regime at the basin scale using a numerical model and to quantify the propagation of surface warming events in aquifers with different groundwater velocities

Data and Method

Results and Discussion

Conclusions