Mendip Hills - Climate

Climate

Along with the rest of South West England, the Mendip Hills have a temperate climate generally wetter and milder than the rest of England. The annual mean temperature is about 10 °C (50 °F) with seasonal and diurnal variations, but the modifying effect of the sea, restricts the range to less than that in most other parts of the United Kingdom. January is the coldest month with mean minimum temperatures between 1 °C (34 °F) and 2 °C (36 °F). July and August are the warmest, with mean daily maxima around 21 °C (70 °F). In general, December is the dullest month and June the sunniest. The south-west of England enjoys a favoured location, particularly in summer, when the Azores High extends its influence north-eastwards towards the UK.

Cumulus cloud often forms inland, especially near hills, and reduces exposure to sunshine. The average annual sunshine is about 1,600 hours. Rainfall tends to be associated with Atlantic depressions or with convection. In summer, convection caused by solar surface heating sometimes forms shower clouds and a large proportion of the annual precipitation falls from showers and thunderstorms at this time of year. Average rainfall is around 800–900 mm (31–35 in). About 8–15 days of snowfall is typical. November to March have the highest mean wind speeds, with June to August having the lightest; the prevailing wind direction is from the south-west.

A combination of the rainfall and geology leads to an estimated average daily runoff from springs and boreholes of some 330,000 m3 (72 million imperial gallons). Bristol Waterworks Company (now Bristol Water) recognised the value of this resource and between 1846 and 1853 created a series of underground tunnels, pipes, and aqueducts called the "Line of Works", which still carry approximately 18,200 m3 (4 million imperial gallons) of water a day to Barrow Gurney Reservoirs for filtration and then on to Bristol and the surrounding areas. This collection and conveyance of water from the Chewton Mendip and East and West Harptree areas is accomplished by the effect of gravity on the runoff. Water from the Mendips is also collected in Cheddar Reservoir, which was constructed in the 1930s and takes water from the springs in Cheddar Gorge.