A notably dry interlude in mid-month aside, December was mild and wet with damaging storms early and late in the month. Precipitation totals across much of northern Britain were exceptionally high and most of the English Lowlands registered a 5th successive month with above average rainfall. Generally, this sequence constitutes the terminal phase of the drought but substantial rainfall deficiencies remain in parts of the South West and groundwater level recoveries have only recently been initiated in some eastern aquifers. Despite flood alleviation drawdown in some headwater reservoirs, overall stocks for England & Wales were considerably above average entering 2007 and well above corresponding stocks in 2006. However, stocks remain seasonally low parts of the South West, Colliford in particular. River flows exceeded previous maxima in parts of Scotland and floodplain inundations were common across much of the UK. Substantial recharge since mid November has greatly improved the groundwater resources outlook. The saturated soil conditions are conducive to further replenishment through the late winter but also contribute to the continuing risk of further flooding.
December was a mild month with abundant rainfall over the first fortnight followed by a notably dry spell - in parts of the English Lowlands precipitation was largely restricted to fog-drip over the 10 days from the 16th. The return of cyclonic conditions produced a tempestuous end to the year; damaging storms and substantial rainfall continued into January 2007. The December rainfall distribution reflected the prevailing synoptic pattern. Moist westerlies produced many notable storm totals (e.g 24-hr totals of 115mm at Capel Curig, N. Wales and 102mm at Inveruglas, Strathclyde on the 13th). In many mountainous catchments, these contributed to December rainfall totals of more than twice the 1961- 90 average - a significant anomaly for one of the wettest months of the year. Below average rainfall was largely restricted to sheltered eastern areas (Peterhead reported < 40%) but Cornwall was also relatively dry. Provisionally, the UK registered its 4th wettest December since 1959 and the Oct-Dec period ranks 2nd wettest in over 50 years. The Nov/Dec rainfall was the highest for Scotland in a series from 1914 and, for the Thames closely equates to the combined totals for 2004 and 2005. Most of the drought-affected region (parts of the South West excepted ) continued a sequence of relatively wet months stretching back to August; long term rainfall deficiencies have decreased substantially. 2006 regional rainfall totals are within the normal range but much of western Scotland was notably wet and residual pockets of significant rainfall deficiency remain (e.g. in Cornwall). Such areas aside, the autumn and early winter rainfall provided a clear termination to the meteorological drought.
Although recessions predominated in the 3rd and 4th weeks, December was characterised by sustained spate conditions and floodplain inundations in rivers across much of the country. Flood warnings were common and most catchments were, again, very vulnerable to further rainfall in early 2007. In responsive catchments, the steep late-autumn recoveries in runoff rates continued into December. Very exceptional flow rates were recorded in North Wales, the northern Pennines, parts of Northern Ireland and, especially, rivers draining the Scottish Highlands. New maximum recorded flows were established on a number of Scottish Rivers including the Tay (at Pitnacree), the Teith and Allen Water with records of around 50 years. The Ballathie gauging station on the Tay recorded a remarkable peak of 1705 cumecs on the 14th. Substantial residential and commercial flooding was reported from eastern Scotland (e.g. at Callender, Stirling, Bridge of Allan, Dalguise). In the English Lowlands, where the drought's impact was most compelling, a seasonally late recovery in runoff rates gathered momentum in most permeable catchments. After depressed autumn flows, December runoff totals for most spring-fed streams returned to the normal range (the Darent in Kent was an exception), typically exceeding Dec. 2005 flows by a wide margin. For the Lambourn, flows approached the monthly mean after more than two years with seasonally depressed flows. Monthly runoff totals established new December records across much of northern Britain; the Earn exceeding the previous maxima in a 59-yr series. Elsewhere runoff totals were generally well within the normal range. Accumulated runoff totals provide echoes of the sustained drought conditions. Despite a modest upturn in the Mimram flows, the 2006 runoff was the 2nd lowest annual total in a 55-yr series and long term accumulated runoff deficiencies remain large across southern England.
With soil moisture deficits eliminated across almost all outcrop areas, the December rainfall was very beneficial for aquifer replenishment (helped by the moderate intensity of the frontal rainfall). Over wide areas, the period since mid-November has been the most productive for infiltration since late 2002, and estimated recharge has exceeded that for the full 2004/05 recharge season in some areas (e.g. parts of the North Downs). However, at many index sites - particularly where autumn groundwater levels were very depressed - much of this abundant recharge had yet to reach the water-table when the December levels were reported. Late-reporting wells in responsive aquifer units have captured notably steep recoveries with recent rises of 20 metres or more in some Chalk and Limestone outcrops areas (e.g. Rockley, Chilgrove, Alstonfield) - commonly leaving levels at their highest for at least three years. In the slower responding Chalk of the Chilterns (Stonor) modest upturns have been registered but the 2006 maximum levels should be exceeded in January. The storage characteristics of the Permo-Triassic sandstones of the Midlands ensure that the post-drought recovery is likely to be slow but the Weeford Flats borehole is no longer dry and levels rose smartly at Nuttalls Farm through December. The last 8-10 weeks has seen a very major improvement in groundwater resources and the outlook is substantially healthier than a year ago.