  In this paper, we analyze water ice occurrences at the surface of Mars using
near-infrared observations, and we study their distribution with a climate
model. Latitudes between 45{\deg}S and 50{\deg}N are considered. Data from the
Observatoire pour la Min\'eralogie, l'Eau, les Glaces et l'Actitit\'e and the
Compact Reconnaissance Imaging Spectrometer for Mars are used to assess the
presence of surface water ice as a function of location and season. A modeling
approach combining the 1-D and 3-D versions of the General Circulation Model of
the Laboratoire de M\'et\'eorologie Dynamique de Jussieu is developed and
successfully compared to observations. Ice deposits 2-200 \mu m thick are
observed during the day on pole facing slopes in local fall, winter and early
spring. Ice extends down to 13{\deg} latitude in the Southern Hemisphere but is
restricted to latitudes higher than 32{\deg} in the north. On a given slope,
the pattern of ice observations at the surface is mainly controlled by the
global variability of atmospheric water (precipitation and vapor), with local
ground properties playing a lower role. Only seasonal surface ice is observed:
no exposed patches of perennial ground ice have been detected. Surface seasonal
ice is however sensitive to subsurface properties: the results presented in
this study are consistent with the recent discovery of low latitude subsurface
ice obtained through the analysis of CO2 frost.
