  We study the intriguing analogy between gravitational dynamics of the horizon
and thermodynamics for the case of nonstationary radiating spherically
symmetric black holes both in four dimensions and higher dimensions. By
defining all kinematical parameters of nonstationary radiating black holes in
terms of null vectors, we demonstrate that it is possible to interpret the
Einstein field equations near the apparent horizon in the form of a
thermodynamical identity $TdS=dE+PdV$.
