Hi Suzie, if you're the desert and growing fig trees. Here is what I recommend:
Temps are high at day and cool or normal at night. By high I'm saying 95+ degrees. I'm in Charlotte, North Carolina and its starting to get hot (85+ degrees) here and humid because we get afternoon showers and then more sun. For starters, you're going to have to mulch your trees heavily. Second, dumping one full gallon or 2 onto a tree at one shot may not work. You're going to have to provide your trees with a drip emitter using 1 gallon emitters. Jon and I talked about this last year and there maybe a post about it too but the problem is the water will just roll off or around the root system. BUt a drip system gets the water down to the root system constant over time.
I have over 247 fig trees in 30gal container. All of these trees are on a drip emitter system. I give each tree 1/2 g of water everyday unless it rains. Some trees are so root bound and for those I just add another 1/2g emitter. I water my trees at 3AM for one hour. This is for a normal 85 degree day of sunshine. If temperature are projected to reach 95 or more, then I will water them again at 12PM for another hour.
If I was in the desert, I would water twice a day using a 1gal emitter for 1hour at seperate times. If I was using 1/2g emitters, then I would water 3 times a day, 7am, 10am and 2PM. The mulch help keep your trees a little cool. Hope this helps!