SHAFAQNA – The Grand Ayatollah Vahid Khorasani answered a question about fasting in countries with unusual days and nights.
Question: In some countries, days and nights are unusual, for example sometimes the night is 22 hours and the day is just 2 hours, or vice-versa; what is the ruling about fasting?
The Grand Ayatollah Vahid Khorasani: Fasting must be done from Dawn’s call to prayers (Fajr Adhan) until evening (Maghrib Adhan), even if the day is long. And if in the middle of the day, the fasting becomes so difficult that customarily cannot be tolerated, can drink water and food to the amount to deal with difficulty and fast the rest of the day, and must compensate for that day by fasting later on (Qadha).
Source: PERSIAN SHAFAQNA