Why does your parquet floor get cracks in wintertime?
Wood is a material that adapts to the humidity, environment's climate, which explains why the wood shrinks and swells.

Shrinking in winter and swelling in summer is a natural phenomenon of wood. The different finishing layers (oil, varnish, wax) have no impact on it, since they delay the exchange of humidity between wood and its environment, but never prevent it from happening. Do you have cracks that are larger than 1mm in your wood? In that case, adjusting the humidity level is recommended.

In the winter, when your home is artificially heated, humidity drops. You can easily check the humidity values using a hygrometer. In ideal conditions, the humidity is between 45% and 55%. Are the values too low? To regulate humidity, you can use a humidifier. These devices evaporate water to increase humidity in the air.

If you don't foresee additional humidification in the space, your parquet will inevitably dry out, which leads to flakes and cracks. 

Would you rather avoid that?

Limit venting and ventilating the room. When it's freezing outside, it's better to completely open the windows or doors for a short period of time, instead of having a continuous supply of dry outdoor air.
Spread more humid air. By not immediately drying the walls and the floor after a shower or bath, and keeping the bathroom door open, you increase the humidity level in the home.
Don't set the heating too high. The (floor)heating of a house has a lot of influence on the humidity level. Warm air dries out more.
Use a humidifier. To regulate humidity, you can use a humidifier. These devices evaporate water to increase humidity in the air.