I have had this problem in older Volvos and the cause are leaves and tree droppings clogging the drain tubes that run down the left and right windshield pillars. The gasket around the hatch is designed to shed ninety or so percent of the water and what gets past them is sent down the tubes. Get a source of compressed air and blow the tubes clear of junk from years of bits and things going down them. Do you park it with the hatch open under trees?