Shieldwall uses a 12 turn per year calendar.
We use the old german calendar names for the months of the year.
Seasons are quite harsh in shieldwall: if you are running on 0 food during the fall expect to be below 0 on the first turn of winter! You cannot simply maintain a minimal level of food and expect to survive the winter without enduring shortages.

Build granaries to store food, and run a surplus to help you survive the winter.