Effect of evaporation on the concentration of a saturated solution
When a solution is saturated, it contains the maximum amount of solute which can be dissolved at that particular temperature. So effectively it is at its "maximum concentration" (for a given temperature).

This means that if your solvent is evaporating and the temperature remains constant, then solute will precipitate out of solution. The concentration of the solution will still be at its maximum as you are concerned with the amount of solute dissolved.

If you are heating up the solution in order to evaporate the solvent then the increase in temperature might mean that your solute solubility increases. This will depend on what solvent/solute you have.

However, a saturated solution which cools down without being disturbed may form a super-saturated solution whereby its concentration has gone beyond the solubility of the solute at that temperature.