February began with the most sustained and damaging snow episode experienced across large parts of southern Britain for a generation. By contrast, the latter half of the month was largely dry and mild. February precipitation totals in many, mostly western, areas were well below average and reservoir stocks declined considerably in some large impoundments (e.g. in north-west England and western Scotland). Overall stocks for England & Wales fell to within 1% of the long term average for early March. Nonetheless, stocks in almost all index reservoirs exceeded 90% of the early spring average; most remain close to capacity. Frozen catchment conditions resulted in steep recessions in many responsive rivers during early February but sustained frontal rainfall early in the second week, supplemented by a substantial snowmelt contribution, triggered widespread flooding; flood warnings were common around the 9-10th in southern and eastern Britain. In many western catchments however, February runoff totals were well below average. Precipitation patterns during the month generally favoured the major aquifers and groundwater levels, although seasonally below average in some western outcrops, were above, to well above, the late- winter average. Overall water resources have held-up well through the UK's 2nd driest winter since 1996/97; the outlook remains generally healthy but, this year, the amount and distribution of spring rainfall will be particularly influential.
Very wintry conditions characterised early February - exceptionally low temperatures accompanied by the most widespread snowfall since the winter of 1990/91. Accumulated snowfall exceeded 50cm over the first week in some upland areas (e.g. Dartmoor); as remarkably, daily totals exceeded 25cm in some low-lying districts (e.g. Epsom, Surrey). Across the country, thousands of schools closed - partly due to the major transport disruption as snow cover extended over seven days or more. Further substantial precipitation (a mixture of rain, sleet, snow and hail) was recorded across southern England on the 9/10th (the Scilly Isles reported 63mm and many catchments registered >25mm). Thereafter, northern Britain was wet around the 15/16th but high pressure was generally dominant - bringing mild, dull and dry weather. Some areas (e.g. Oxfordshire) registered <2mm of rainfall over the last 16 days of the month. February precipitation patterns reflected the limited influence of Atlantic frontal systems. Monthly totals were well above average in most of eastern Britain - exceeding 150% in parts of eastern Scotland and much of SE England whilst many western catchments reported <50% of the February average. Provisional data indicate that both Northern Ireland and the EA Wales region reported their 2nd lowest February rainfall since 1986. As notably, many western catchments registered their 5th or 6th driest winters in the last 45 years and, nationally, it was the coldest Dec-Feb since 1995/96 - such a combination contrasts dramatically with the generality of winters in the recent past. Longer term regional rainfall accumulations are mostly well above average.
Sustained late-January river flow recessions continued into February and, with headwater catchments frozen in many areas, river flows were seasonally low during much of the first week. Following the storms on the 8/9th across southern Britain, river flows recovered very briskly (snowmelt was a significant factor). Provisional data indicate that the Kennet, Dorset Stour and Taw were among those rivers establishing new maximum February peak flows. Flood warnings were very widespread on the 10th; tidal blocking was an exacerbating factor in some coastal areas. Floodplain inundations were generally moderate but localised flooding was widely reported (e.g. in Yeovil, Watford and parts of West Berkshire). A week later spates were common across parts of northern Britain; the River Naver registered its 2nd highest February flow on record - in a 30-year series. Recessions became firmly re-established over the latter part of the month but February runoff totals were still considerably above the average throughout the English Lowlands. By contrast, very modest runoff characterised many western catchments - the Luss Water registered its 2nd lowest February runoff for 23 years. A similar, but more muted, geographical contrast may be recognised in the winter (Dec-Feb) runoff totals. Initial estimates indicate that Northern Ireland registered its 5th lowest winter runoff in a series from 1981.
Generally, the February rainfall distribution was very beneficial from a groundwater resources perspective; most of the English Lowlands reported >120% of the monthly average. With soils close to saturation throughout the month, conditions were very favourable for substantial late-winter recharge - but frozen ground restricted infiltration through the coldest part of the month. Modelled estimates of infiltration exceeded twice the average in parts of the Chalk outcrop and observational evidence confirms exceptional groundwater level increases in the southern and eastern Chalk (e.g. in the South Downs and on the Isle of Wight). February groundwater levels in almost all the Chalk index wells and boreholes were considerably above average. Levels in most limestone outcrops were also close to, or above, average. The Permo- Triassic sandstones outcrops present a spatially more varied picture (in part, a consequence of large differences in responsiveness of the index sites). Healthy groundwater levels characterise most slow- responding wells in the Midlands and a steep increase was recorded at Bussels in the South West. By contrast, notably low levels were reported for the Newbridge well in Dumfries and Galloway. With very modest soil moisture deficits and an unsettled start to March, a seasonally early onset of the seasonal recession in groundwater levels is unlikely. Groundwater resources are healthy throughout most major aquifers but rainfall over the next 6-8 weeks will be influential in determining the range of groundwater levels through the summer of 2009.