  To study the effects of galactic winds on the stellar metallicity
distributions and on the evolution of Draco and Ursa Minor dwarf spheroidal
galaxies, we compared the predictions of several chemical evolution models,
adopting different prescriptions for the galactic winds, with the
photometrically-derived stellar metallicity distributions of both galaxies. The
chemical evolution models for Draco and Ursa Minor, which are able to reproduce
several observational features of these two galaxies, such as the several
abundance ratios, take up-to-date nucleosynthesis into account for
intermediate-mass stars and supernovae of both types, as well as the effect of
these objects on the energetics of the systems. For both galaxies, the model
that best fits the data contains an intense continuous galactic wind, occurring
at a rate proportional to the star formation rate. Models with a wind rate
assumed to be proportional only to the supernova rate also reproduce the
observed SMD, but do not match the gas mass, whereas the models with no
galactic winds fail to reproduce the observed SMDs. In the case of Ursa Minor,
the same model as in previous works reproduces the observed distribution very
well with no need to modify the main parameters of the model. The model for
Draco, on the other hand, is slightly modified. The observed SMD requires a
model with a lower supernova type Ia thermalization efficiency ($\eta_{SNeIa}$
= 0.5 instead of $\eta_{SNeIa}$ = 1.0) in order to delay the galactic wind,
whereas all the other parameters are kept the same. The model results, compared
to observations, strongly suggest that intense and continuous galactic winds
play a very important role in the evolution of local dSphs.
