Fiddle Leaf Fig Help!

My fiddle leaf fig has dropped most of its leaves but growing new ones from the top. 

I live in Australia and have been watering only when soil is dry..between a week and two weeks. However over the last two weeks the leaves have gradually been falling. 

It has been hot..more in the 40 degree Celsius range so should I have watered more frequently? I just don't understand how it can be growing new leaves with the others dying. 

Any help much appreciated!