Brown leaves on eucalyptus planted in New Zealand
Previously healthy tree of 20 metres suddenly leaves turned brown and over a six week period still brown but not dropping much.
Certified GKH Gardening Expert
Yes, wait and see how it does this spring and summer. It may be frost damage, from the characteristic partial browning on one side. If a hard freeze is sustained for a few days the Eucs can be killed; if only for a night or two, they brown like yours and then recover the next growing season.
Consider creating a drainage system for the lower property; dig a channel, install drain tiles or whatever is appropriate.