I don't know much about Israel, so I'm going to guess. First, I suspect the water or soil has a pH that's a bit too high. Secondly, it may be hot so that the plant can't always move enough water from the roots to the leaves and they dry out a little. You can put a small spoonful of vinegar in the water from time to time and see if the new leaves become green. Secondly, can you shade the tree by putting it under a larger shrub during very hot weather? I am much colder than you, in Canada, but I have lots of chestnuts at home. :) Good luck with your tree.