Global warming should increase evapotranspiration rates. Soluble salts from saline water tables can reach the soil surface more easily under such conditions, yielding a higher extent of the saline area in agricultural lands. A mechanistic modeling application for dealing with this problem is presented, estimating the saline area increments due to global change in a small catchment at the South East extreme of Cuba. The semi-arid conditions of the zone shall be enhanced, according to climate change forecasts. As cattle's raising is the main economical activity in the catchment, daily grass evapotranspiration values (ET) were calculated from an autorregressive model considering real values of the meteorological variables and the forecast. The calculated ET values and the soil hydraulic properties (obtained from pedotransfer functions) were used as input in the mechanistic model. The new water table depths from a maximum capillary-raising depth of 2 m were estimated through the model. Soil salinisation in the catchment was characterized from soil Electrical Conductivity measurements at several depths. This information was introduced in a GIS, as well as the topographical altitudes. AGIS analysis was performed with this data, determining the actual salt-affected area and those predicted under the forecasted climate changes. The saline area increments in the catchment depend upon the climate change scenarios and upon the catchment topography.