My lemon tree is 15 plus years old and has grown to be very healthy and fruitful.. until recently.

The tree and my permanent home is in San Francisco where it stays mostly in the range of 50-65 F all year long. I was attending school out of state until recently and when arriving home, discovered that the top branches of my lemon tree have died (no leaves and when I scratched the bark with my nail, there was no green.)

After inquiring with my family and learning it has been unusually warm, I was concerned that the tree wasn't getting enough water (because my family doesn't water the garden at all.) I began watering the tree more frequently instead of solely relying on it's deep roots in the soil.

Unfortunately it's been a month since I returned home and the tree still continues to drop leaves, perhaps even more than normal and branches continue to die.

I'm becoming very concerned. Even if the tree bounces back and recovers, I am worried because all the branches he is losing are on the top and in the back; If I prune the dead branches off, he will become very lopsided and may threaten to tip over (?) or crack (?) or I have no idea!

Please help!