Did you have very heavy long term frost where it is planted last winter? Between that and the drought it has probably become over stressed. Check to see if the branches are still alive by scraping away a little of the bark with a finger nail. If it is green underneath all is well. You can cut it right back and it will regrow from the stump.

Our large Crinodendron hookerianum was cut back to the ground by winter cold this year but, as MG says, is now regrowing from the very base. Our Crinodendron patagua appears to have been killed altogether though....

If yours is dropping foliage now (rather than earlier in the year) it would suggest that it has suffering from quite severe drought. They should be grown in semi-shade rather than full sun, but might have needed watering through the long recent dry spell in either position.