Estimations of the past groundwater recharge rate from deep borehole temperature data

In order to estimate the past groundwater recharge rates from deep borehole temperature data, observed temperature–depth profiles are compared with the profiles calculated from heat conduction–convection equation under the condition of linear increase in surface temperature due to global warming and urbanization in Tokyo metropolitan area. The results show the increase in groundwater recharge rate from the 1890s to 1940s, and it decreased from the 1940s to 1990s. These estimations agree well with the precipitation record in Tokyo during the last 100 years. Therefore, the deep borehole temperature data can be used for estimating not only surface temperature history but also the past groundwater recharge rate in Tokyo area.