Watering and maintenance for Canary Island date palms in Arizona

[palms23]

I've got three palm trees in my front yard which I believe are Canary Island date palms. I've had them since I moved into the house about 15 years ago. For most of that time, I've barely done any maintenance or watering of them, I have just left them alone for the most part. Recently, over the past few years I've noticed that they seem to be losing fronds. I imagine there's some variation by season, but there's clearly an overall trend downward (fewer fronds, green fronds not extending as far).

In just the past three years, I've started watering them a bit now and then during the hot months (like April to September), but not with much consistency. Maybe 2-4 times a year. When I water, I'll turn on the hose, set it at the tree's base, and leave it for 5-10 minutes at each tree. It seems like this may be helping some, but I'm also worried that I could be under/overwatering or that there are other steps I should be taking.

Pictures attached, showing then and now.  There are two trees on the north side (one smaller, one bigger) and one tree on the south side (big).

I'd definitely appreciate any thoughts from folks, and in particular suggestions for:

1. What I can do or change to prevent the trend of decreasing frond density
2. In general, how best to care for them (maybe changing how/when I water or using some kind of fertilizer)