Does anyone know what’s wrong with my horse-chestnut tree

I didn't mean to say the trees were really dying, what I meant is that the LEAVES are dying - not the trees themselves! The leaf miner damage is clearly visible in one of my photos & it is this that is doing the most damage to the trees. A bit of drought they can take as they are trees that were planted alongside the paths on the housing estate 60 years ago. There must be several 100 Horse Chestnut trees on the estate most of which have survived during the last 60 years.

Just today my wife had an appointment at the eye clinic at our local hospital. This hospital was built in the immense grounds of Hinchingbrooke House Park. The access roads probably followed some of the original roads through the grounds as there are several rows - long lines - of Horse Chestnut trees lining them. As we went past them on the bus I saw many. many really old trees also defoliated. In fact some were in an even worse state than the "youngsters" in my photos. There are trees that must be a couple of centuries old that have been defoliated as well.

Other years in May I've taken pictures of them in bloom & so many together & such enormous trees make a magnificent sight!

 

I'm pretty sure its mostly leaf miner that is causing the problems with horse chestnut early leaf fall.
Apparently HC native to Asia and S. E. Europe so I'm pretty sure they can handle a drought or two.

In my street we have crab apple trees and the leaves usually start falling around now, I think in most cases the trees are just getting rid of insect damaged leaves when they fall early.