Below grade roof water discharge is poor roof water discharge practice.
Downspouts should discharge water above grade. Downspouts collect water from the gutter discharge exit points.
Discharging roof water below grade can come with unexpected consequences.
Below grade drain pipes can become clogged, or break below grade due to shifting soil, or damaged from water inside the drain freezing. Water can expand up to 9% its volume damaging the drain pipe below the soil dispersing water in that area when thawed causing soil erosion when an underground downspout malfunctions. Water problems can likely develop and flow towards the basement foundation leading to unexpected consequences.
Downspout placement is important. To prevent water from seeping into the home from downspouts; Proper placement. This is the key to keeping water away from the home's foundation.
Rule of thumb. Above ground downspout extension placed 6' to 8' feet on the highest point on the lot, in that area, allowing roof water to discharge atop the ground flowing downstream, away from the home.