A Temperate Climate

As in the rest of the British Isles, the climate of Exmoor is a temperate one. That means some rainfall all year round and a relatively small seasonal and daytime fluctuation of temperatures.

The British Isles are in a maritime temperate zone, where the climate is influenced by the sea, keeping the air moist and reducing temperature extremes. The sea takes much longer to warm up and cool down than the land surface. The water in the Bristol Channel is warmest in the autumn and the heat retained through the winter tempers the effects of colder winds and air masses from the north and east. The western side of Britain benefits from the North Atlantic Drift extension of the Gulf Stream current, bringing warm waters from the Carribbean and the temperature of the water in the Bristol Channel can be 10°C in winter, only 6°C less than its summer average.

Exmoor, however, is an area of varied relief. It can range from sea level to 520metres above sea level in the short distance of 5 miles. Average figures for the climate of Exmoor could be given but would mean very little. Because of its southerly position in Britain but its relatively high altitude, its average climate would be like parts of the English Midlands. However, because it is such a varied area, there are few parts of Exmoor with that sort of climate.

Upland microclimates

Upland areas will inevitably have a different climate as temperatures drop, according to the Environmental Lapse Rate, by 6.5 °C per thousand metres. But as far as microclimates are concerned, it is the presence of warm, anabatic, up-valley winds during the day and cool, katabatic, down-valley winds at night that give some upland areas very distinctive microclimates. There are also important differences in precipitation amounts, with a föhn effect causing leeward areas to be in a rain shadow, receiving less rainfall than windward slopes.

Coastal microclimates

Coastal areas have land breezes and sea breezes that are generally mild during the winter months and cool in the summer. A warm, onshore breeze might also result in the build-up of advection mist or fog on the coastal fringe, with the warm, moist air coming into contact with the cold land surface. This results in the condensation of the water vapour and the creation of mist or fog, which gradually clears as one moves further inland away from the breeze.