They suffer lack of vigour in these conditions and tend to droop, become loose in the branches and trun brown in patches. Only in sheltered coastal conditions do they cope reasonably well.
As a species, in the right climate, it can send down deep roots and it is very drought resistant. Water-logging, even persisently wet soil, leads to reduced air capacity and roots die.
A tree replaced just this year could be suffering either drought, not enough water, or airlessness in the soil due to over-watering. A drip system can be good as it allows air to penetrate but you need to get the balance right. Also it is possible that the water is going down but is blocked and backing up so that the bottom part of the root ball is too wet.
Just at the edge of the root ball, make a small narrow hole with a trowel to inspect the soil and see if you can glean more information on the root conditions and act accordingly.