Evaporation over the British Isles

Theoretical values of average annual evaporation from the British Isles are calculated from long‐term averages of air temperature, duration of sunshine, vapour pressure and wind speed for about 100 stations. Direct estimates of the same quantity are obtained from long‐term averages of annual rainfall and annual run‐off from about 40 catchment areas. The two kinds of estimate agree and are plotted on a map to show the geographical variation of evaporation. This shows an increase from 14 in. per annum in Scotland to 20 in. along the south coast.