Simulation of Heat Flow in a Synthetic Watershed: The Role of the Unsaturated Zone

Future climate forecasts suggest atmospheric warming, with expected effects on aquatic systems (e.g., cold-water fisheries). Here we apply a recently published and computationally efficient approach for simulating unsaturated/saturated heat transport coupled flow (MODFLOW) (MT3D-USGS) models via synthetic three-dimensional (3D) representation of temperate watershed. Key aspects needed realistic at the watershed-scale include drivers, layering scheme, consideration surface-water groundwater interactions, evaluation parameters influencing flux. The unsaturated zone (UZ), which is typically neglected in simulations, primary focus analysis. Results from three model versions are compared—one that neglects UZ heat-transport processes two simulate through (1) moderately-thick (2) approximately double thickness. watershed evaluated terms temperature patterns trends UZ, water table, below table (in system), along stream network. Major findings are: Climate forcing product infiltration temperatures rates; they combine into single inflow function. acts as low-pass filter pulses migrating downward, markedly dampening warming recharge signal. (3) effect also buffered by mixing discharge points where shallow deep converge. (4) lateral extent riparian zone, defined near land surface (<1 m), plays an important role determining short-term dynamics baseflow response to forcing. Runoff generated areas particularly periods when rejected during warm wet generates extra runoff low-lying water.