I recently had to travel for work. That time I had to travel 100+ miles in non AC car during hot weather (+100 F) while fasting hour itself is long here (17 hour). I had to sweat quite a lot during my travel which possibly made me dehydrated. I don't really know but I think dehydration can make you delusional or angry. If this is true, this might cause an accident as I was driving by myself. Furthermore, I think a doctor would recommend to keep my body hydrated in such hot weather.
What is the Islamic ruling in this case?
Is it still compulsory, optional, or makroh?