Temperatures of adjacent coastlands are reduced when on - shore winds blow over cold currents because the

The temperatures of adjacent coastlands are reduced when on-shore winds blow over cold currents primarily because the cold currents influence the temperature of the prevailing winds.

Here's how it works in simple terms:

When winds blow over the ocean surface, they pick up characteristics of the water beneath them. If these winds travel over a cold ocean current, the air they carry becomes cooler. As this cooler air moves onto the coastlands, it brings down the temperature of those areas. This is why coastlands experience reduced temperatures when on-shore winds carry the chill from cold ocean currents.

So, the key factor here is the cooling effect of the cold water, which cools the air above it, consequently lowering the temperature of the coastal regions the wind blows onto.