Fig. 4

Assessing the impact of climate change on temperature gradients at different depths. Changes in temperature profile associated with climate change. Lithology is granite. Temperature gradients are shown in 8 cases: 10 K km⁻¹, 20 K km⁻¹, 30 K km⁻¹, 40 K km⁻¹, 50 K km⁻¹, 60 K km⁻¹, 80 K km⁻¹, and 100 K km⁻¹. a The initial condition, and b, c, d, e, and f show the condition after 100 years. Based on Fujibe (2012), the trend of temperature rise over the past 100 years is expressed using five cases (0.88 °C per 100 years, 1.00 °C per 100 years, 1.10 °C per 100 years, 1.60 °C per 100 years, and 2.08 °C per 100 years) according to population density. g, h, i, j, and k show the temperature gradient ratios after 100 years from the initial condition for these five cases. Calculations are performed for each of the five intervals (60–80 m, 80–100 m, 100–120 m, 130–150 m, 180–200 m) shown in b, c, d, e and f. If the observed temperature gradient is Gobs, the corrected temperature gradient is Gcor, the temperature gradient 100 years ago is G(T = 0), and the currently estimated temperature gradient is G(T = 100), then G_cor = G_obs × G(T = 0)/G(T = 100), the reciprocal of the y-axis in this figure multiplied by the observed temperature gradient