Impact of Urbanization and Climate Change on Aquifer Thermal Regimes

We evaluated the past impacts of urbanization and climate change on groundwater-in particular, aquifer temperature-in the Sendai plain, Japan, and further compared with the probable changes due to changing climate in the future. A series of simulations were performed and matched with the observed temperature-depth profiles as a preliminary step for parameter calibration. The magnitude of ground surface warming estimated from subsurface temperature spans 0.9-1.3°C, which is consistent with the calibrated ground surface warming rates surrounding various observation wells (0.021-0.015°C/year) during the last 60 years. We estimate that approximately 75% of the ground surface temperature change can be attributed to the effect of past urbanization. For the climate predictions, climate variables produced by the UK Hadley Centre's Climate Model (HadCM3) under the A2, A1B and B1 scenarios were spatially downscaled by the transfer function method. Downscaled monthly data were used in a water budget analysis to account for the variation in recharge and were further applied in a heat transport equation together with the estimated ground surface warming rates in 2080. Anticipated groundwater recharge under the projected climate in 2080 would decrease by 1-26% compared to the 2007 estimates, despite the projected 7-28% increase in precipitation, due to a higher degree of evapotranspiration resulting from a 2.5-3.9°C increase in surface air temperature. The overall results from the three scenarios predict a 1.8-3.7°C subsurface temperature change by 2080, which is notably greater than the previous effect of urbanization and climate change on aquifer temperature in the Sendai plain.