From what I remember Pecans respond very well to high or low rainfall. During high rainfall foliage and nuts grow like crazy...so much that the branches get so heavy they break off at times. With lesser amounts of rain I assume the opposite happens.

We have had a dry summer (even for Albuquerque!)so perhaps it is responding as you say: depending on the water available: dry season ... small leaves? Lawn watering each week has been the same for the side roots though less rainfall but I'd expect the deep tap roots I was told pecans have would after 30 + years to go down to the water table by now?

Hopefully uf we get a regular rainfall later the tree will put out more & bigger leaves next year. Woukls sure hate to lose that pretty shade tree!