Climate models have traditionally only represented heat and water fluxeswithin relatively shallow soil layers, but there is increasing interest inthe possible role of heat and water exchanges with the deeper subsurface.Here, we integrate an idealized 50 m deep aquifer into the land surfacemodule of the GISS ModelE general circulation model to test the influence ofaquifer–soil moisture and heat exchanges on climate variables. We evaluatethe impact on the modeled climate of aquifer–soil heat and water fluxesseparately, as well as in combination. The addition of the aquifer to ModelEhas limited impact on annual-mean climate, with little change in global meanland temperature, precipitation, or evaporation. The seasonal amplitude ofdeep soil temperature is strongly damped by the soil–aquifer heat flux. Thisnot only improves the model representation of permafrost area but propagatesto the surface, resulting in an increase in the seasonal amplitude of surfaceair temperature of > 1 K in the Arctic. The soil–aquifer water and heatfluxes both slightly decrease interannual variability in soil moisture and inland-surface temperature, and decrease the soil moisture memory of the landsurface on seasonal to annual timescales. The results of this experimentsuggest that deepening the modeled land surface, compared to modeling only ashallower soil column with a no-flux bottom boundary condition, has limitedimpact on mean climate but does affect seasonality and interannualpersistence.
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