Hi Lars,
The temperature of the recharge infiltrating through the ground surface is usually applied by a first kind heat BC on the models' top. EDIT: If you don't use a first kind heat BC and the flow recharge is set by source/sink (elemental material parameter), the flux will adopt the REFERENCE temperature when it enters the model. You can verify this in the Reference Manual, page 55, Eq. (3-17) for an unconfined aquifer: The last term reads ?[sup]f[/sup]*c[sup]f[/sup]*Q[sub]?[/sub]*(T-T[sub]0[/sub]) = Q[sub]T[/sub] (the overlines on the Q's missing...). Q[sub]?[/sub] refers to the flow source sink, Q[sub]T[/sub] is the resulting heat flux, which shall here be 0. Distributing and equating yields T = T[sub]0[/sub]; T is the node temperature and T[sub]0[/sub] the reference temperature.
Cheers,
Bastian