Simulating subsurface temperature under variable recharge

A distributed numerical model utilizing MacCormack finite difference method is developed to simulate the transient subsurface temperature profiles under time varying groundwater recharge. It is not restricted to constant percolation rate and sinusoidal temperature variations as is the case in most models. The model is validated with the data available for the Nagaoka plain, Japan showing good agreement for the computed subsurface temperatures having correlation coefficient (as R 2) and root mean square error (RMSE) as 0.89 and 0.42, respectively. The model is employed to investigate the alteration in the subsurface thermal regime due to variable recharge resulting from precipitation in South Korea. Results reveal that the subsurface thermal regime is influenced significantly by the temporal variability in groundwater recharge and temperature at the surface, and subsurface temperatures are not necessarily sinusoidal at all depths. Seasonal variations and the effect of short term hydrological phenomena are clearly depicted in simulated results. The temporal variations of the subsurface temperature are highly nonlinear near the ground surface and become almost linear beyond 10 m. The subsurface temperature profiles vary significantly from one cycle to other and tend to be vertical beyond 15 m. Its variability also depends upon the Peclet number.