Usually when leaves show interveinal yellowing like that, it's an indication that water isn't getting into the leaves. This could be due to a number of factors (vascular disease, root rot, girdling roots, insects, etc.). It looks like this tree has a lot of dieback already. I would suggest pruning one of the declining (not completely dead) branches and checking the cut end for any discoloration, which can be an indication of disease. Feel free to send a declining branch sample to our lab so we can check for or rule out disease, submission information can be found here: https://www.udel.edu/academics/colleges/canr/cooperative-extension/sustainable-production/plant-diagnostic-clinic/