Actually the PHB states that it absorbs the damage not deflects it. It even specifies that he ward has hit points equal to.. and what happens once the ward reaches 0 hit points. In my view the arcane ward is not a barrier, it is a strand of magic that absorbs damage (any type of damage) but that is all.
No concentration check is required because only if you take damage from an attack do you need to roll concentration checks.
Otherwise that is quite a powerful ability wouldn't it give the caster virtual immunity to any effect from melee until the ward is gone.
For example the aforementioned wizard has 20hp left to his arcane ward, he is struck by a Paladin using blinding smite. He takes 15hp damage from the attack (which the ward absorbs) does he or doesn't he have to make a saving throw or be blinded? Or better still he is invisible and is struck by the same paladin using branding smite and takes only 10 hp damage which the ward absorbs is he now visible or not?
He is attacked by another wizard with a chill touch cantrip same deal the 4 points of necrotic damage is absorbed by the ward can he regain hit points as normal?
Guiding bolt same deal 10 hp absorbed by ward does next attack have advantage or not?
Heat metal damage absorbed by ward, does target have to save or drop item?
Ray of Frost absorbed by ward, is the targets speed reduced?
Ray of sickness, does the target have to save vs poison?
Shocking grasp, electrical damage absorbed by ward, can or cannot the target take reactions?
Staggering smite...
You get the idea. It would be quite a powerful spell.
mk