  Gas clouds are present in the Galactic centre, where they orbit around the
supermassive black hole. Collisions between these clumps reduce their angular
momentum, and as a result some of the clumps are set on a plunging trajectory.
Constraints can be imposed on the nature of past accretion events based on the
currently observed X-ray reflection from the molecular clouds. We discuss
accretion of clouds in the context of enhanced activity of Sgr A* during the
past few hundred years. We put forward a scenario according to which gas clouds
bring material close to the horizon of the black hole on <~0.1 parsec scale. We
have modelled the source intrinsic luminosity assuming that multiple events
occur at various moments in time. These events are characterized by the amount
of accreted material and the distribution of angular momentum. We parameterized
the activity in the form of a sequence of discrete events, followed the viscous
evolution, and calculated the luminosity of the system from the time-dependent
accretion rate across the inner boundary. Accreting clumps settle near a
circularization radius, spread there during the viscous time, and subsequently
feed the black hole over a certain period. A significant enhancement (by factor
of ten) of the luminosity is only expected if the viscous timescale of the
inflow is very short. On the other hand, the increase in source activity is
expected to be much less prominent if the latter timescale is longer and a
considerable fraction of the material does not reach the centre. A solution is
obtained under two additional assumptions: (i) the radiative efficiency is a
decreasing function of the Eddington ratio; (ii) the viscous decay of the
luminosity proceeds somewhat faster than the canonical L(t)~t^{-5/3} profile.
We applied our scheme to the case of G2 cloud in the Galactic centre to obtain
constraints on the core-less gaseous cloud model.
