There are three main types of rainfall - convectional rainfall, frontal rainfall and relief rainfall. Convectional rainfall may occur in Britain in the summer, after a long hot day, but is most commonly found in places with warmer climates. The ground or water in lakes or seas is warmed by the sun, throughout the day. The air above the land becomes heated. This makes the air less dense, so it rises. As the air rises it cools. Cool air can not hold as much water vapour as warmer air, when the air becomes too cold for the amount of water it holds condensation occurs. The point where this occurs is called the dew point. These drops of condensation form into clouds, gradually becoming tall thunderstorm clouds, called cumulonimbus. When these clouds become too big, containing too much water gravity forces them to release the water in a huge downpour.
Relief rainfall or orographic rainfall is common in the west of Britain. The prevailing winds blow moist air from the Atlantic Ocean to the west of Britain onshore. As the air hits higher land, such as the hills and mountains in Wales and the north-west of England, the air is forced to rise. When air rises above the dew point, it can no longer hold all its water, which starts to condense and form clouds. This type of "rainfall" is called relief because it is affected by the lie; or "orographic" because it is affected by mountains. And this explains why Ireland (or West Britain if analysing 17th century Irish history), is so green.
Hydrological cycle revised, I headed out into the garden to check the winter standing brassicas. Cavolo nero looking magnificent, one or two red cabbages still hanging on in there, but the purple sprouting broccoli has at last come into its own. Thigh high, these vegetables are just calling out to be picked, their leaves squeaky and stiff, their magnificent, glaucous leaves holding the rain drops and looking just so enticing.