December was a mixed month and was subject to a range of weather types, in contrast to the predominantly westerly conditions that prevailed for much of 2017. The UK average temperature was typical for December but mild spells were punctuated with much colder periods, including a widespread wintry interlude mid-month. Generally, December was relatively dry across northern Britain and wetter in the south, which has moderated long-term rainfall deficiencies in the English Lowlands. Correspondingly, Soil Moisture Deficits (SMDs) diminished, while modest groundwater recharge was observed in the majority of boreholes and river flows returned to the normal range in many responsive catchments. While the rainfall was welcome from a water resources perspective, groundwater levels remained notably low in parts of the Chalk and flows were below normal in some groundwater-dominated rivers of southern England. Similarly, while reservoir stocks increased in the south, end-of-December stocks remained below average in some impoundments, e.g. the London group, Wimbleball and Bewl, the latter being 26% below average at month-end (leading to a drought permit application in early January). At least average rainfall is needed through the remaining winter or early spring months in order to reduce the risk of water resources pressure in parts of south-east England later in 2018.
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