2004 national and regional rainfall totals for the UK, together with the corresponding percentages of the 1961-90 average, are shown on Figure 1, individual monthly and half-yearly figures are given in Table 1. At the national scale, rainfall for 2004 was approximately 10% above average adding to a recent cluster of notably wet years - five of the last seven years rank among the 10 wettest in a series from 1914. The 2004 total for Scotland is the 4th highest annual total in a series from 1869 (1990 was considerably wetter). Northern Ireland registered a near-average annual rainfall total whilst the England and Wales total moderately exceeded the 1961-90 average but the regional totals for the Southern and the South-West regions fell marginally below average.
Although most regions of the country were relatively wet, the rainfall distribution through the year was generally unfavourable from a water resources perspective. January, April, August and October were wet months across most of the country but a relatively dry late winter (2003/04) and early spring across the entire country (see Figure 2) raised some concern about possible hydrological stress in the summer of 2004. In the event, a extremely unsettled August (equalling the wettest since 1917) contributed to the 2nd highest June-August rainfall since 1958 for the UK as a whole. Some regional rainfall totals for the summer were outstanding (see Figure 3). Much of the Northumbrian region reported considerably above average rainfall for each of the summer months and the accumulated total eclipsed the previous maximum (in a series from 1961) by a substantial margin. Much of eastern Scotland also had an exceptionally wet summer with only 1985 producing broadly similar totals in the last 45 years at least. Apart from western Scotland and the Islands (much of Northern Ireland also) October rainfall totals exceeded 120% of average but, thereafter, frontal systems mostly followed northerly tracks. As a result the normal north-west/south-east rainfall gradient across the UK was accentuated and significant rainfall deficiencies became established across southern and eastern Britain. Seasonal recoveries in water resources normally gather momentum in November and December but in 2004, the two-month rainfall totals were <60% of average across large parts of eastern, central and southern England (see Figure 4) and for England and Wales as a whole it was the third driest end to the year since 1953.
January was a generally mild and unsettled month but with a freezing interlude late in the month, as an Arctic airflow brought widespread snowfall across much of the UK late in the month. Gales and blizzards were common in northern Scotland but, to the south, mild and damp conditions predominated. Many areas reported only 3 or 4 dry days in the month and vigorous frontal systems produced significant precipitation totals on a number of occasions. Precipitation totals over the last few days of the month were especially impressive (Eskdalemuir reported 62mm on the 28th and parts of Northern Ireland received almost half their January total in the last couple of days); substantial accumulations of snow were also reported (e.g. around 30cm at Fylingdales and Glenlivit on the 28th) - initiating an exceptionally wet spell that continued into February. A few areas, mostly in eastern Scotland, reported slightly below average January rainfall totals but much of Britain exceeded 120% with a few areas (e.g. the North York Moors) approaching 200%. For the UK as a whole, January was the wettest month since October 2002 and all regions registered above average rainfall for the Nov-Jan period (only marginally so in the South-West). Given the low evaporation demands, the positive rainfall anomalies, during what is on average the wettest period of the year resulted in substantial improvements in water resources notwithstanding appreciable long term rainfall deficiencies (from February 2003) remaining, in parts of north-east Britain especially.
A sequence of vigorous frontal systems brought substantial rainfall to most regions in early February but a decisive change in synoptic patterns heralded colder and mostly dry conditions over the ensuing four weeks. In the context of the recent past, snowfall constituted a substantial proportion of total precipitation, in Scotland especially but blizzard conditions were also experienced in coastal areas of England (e.g. at Bournemouth on the 27th). A slow-moving frontal system produced a remarkable 260mm rainfall total over 48 hours (4/5th Feb) at Capel Curig in North Wales - the corresponding return period exceeds 100 years. Substantial rainfall occurred across much of the UK on the 5th but, subsequently, some localities in central southern England reported only 2mm over the three weeks up to March 2nd. Monthly precipitation totals for February exhibited wide spatial variations; North Wales was exceptionally wet and parts of northern Scotland reported >150% of the monthly average also. By contrast, parts of southern England (coastal areas particularly) registered <30% and Northern Ireland recorded its 2nd lowest February rainfall in 20 years. Despite its dry conclusion, rainfall totals for the winter (December-February) were close to, or above, average in all regions but long term deficiencies remained significant, particularly in the 13-month timeframe; the February- February rainfall total for the UK as a whole was the lowest since 1975/76.
March was, at turns, balmy and boisterous with precipitation mostly concentrated in the first three weeks. Gales produced significant rainfall and some wind damage on the 8th (e.g. on the Isle of Wight) and substantial rainfall totals were registered in northern Britain on the 19th (e.g. 60 mm at Loch Glascarnoch, Highland Region). However, many rain-bearing depressions passed to the north of the British Isles and most frontal incursions produced only modest rainfall totals. As a consequence, March rainfall was below average across the UK with the exception of a zone from the Cheviots to Northern Ireland (plus a few other localities). Large parts of eastern Britain registered less than 70% of the March average, the southern Pennines and Cheshire Plain being particularly dry. Regional February-March rainfall totals were generally higher than in 2003 but still well below average in most regions, notably so in the South East. For England and Wales it was the 4th driest such period since 1976. Rainfall over the winter half-year (October-March) was typified by large month-on-month variability but all regions of Britain registered half-year totals in the normal range; Northern Ireland was its driest since 1986 in this timeframe. Longer term deficiencies remained large across much of the UK with a few eastern catchments reporting below average rainfall in 10 of the 12 months since February 2003.
April was very unsettled across much the greater part of the UK and the proverbial April showers were decidely more vigorous than usual. Widespread frontal rainfall also contributed to the well above average rainfall reported in most regions. The 18th was especially wet with much of eastern England and the Borders registering rainfall totals > 20mm. Intense localised downpours were especially common over the final week - triggering localized, mostly urban, flooding. Following a short heat-wave, thunderstorms on the 26th and 27th resulted in some exceptional storm totals e.g. 43mm in 2 hours at Bromsgrove (26th); 33mm in an hour near Sheffield (27th). Further vigorous thunderstorms affected much of southern England as warm, moist air pushed up from France on the 27th. The showery nature of much of the April rainfall made for substantial local variability in the monthly totals but only a few areas - mostly in Wales and north- west England - reported less than 75% of average; Anglesey was especially dry. By contrast, much of the Scottish Highlands registered around twice the April average, with similar percentages characterising parts of the Midlands and the North-East. Regional rainfall deficiencies over the post-January 2003 period remain very substantial but the above average rainfall over the six months since October 2003 has largely banished the spectre of drought.
The sequence of low pressure systems which brought plentiful rain in late April continued into May with many areas reporting only one dry day in the first week; the 3rd was especially wet. Thereafter, anticyclonic conditions dominated synoptic patterns, producing warm and dry weather with notable sequences of dry days, in the west particularly - a number of localities from North Wales to Cornwall registered 22 consecutive dry days. Elsewhere, intense local thunderstorms - on the 19th and 20th especially - contributed to above average May rainfall totals in South-East England (and a few other areas). However, generally, regional rainfall totals were in the 45-90% range with a few areas registering only about a third of average (e.g in parts of the Vale of York and north-east Scotland). The modest UK total added to a cluster of dry Mays in the last 15 years - six being substantially below average. From a water resources viewpoint, medium and longer term deficiencies are of more significance. Some catchments (e.g. in the South West) have reported below average rainfall in 9 of the last 10 months with notable accumulated deficiencies over the August-May period. In this timeframe Northern Ireland and the Tay basin both registered their lowest rainfall since 1973; the South West was almost as deficient.
June was a month of contrasting weather patterns. The unsettled weather of late May continued with significant rainfall in northern Britain - Tain Range (Highland Region) reported 38mm on the 11th - but rainfall amounts were very modest in the South and, with high pressure dominating, some localities (e.g. in south Oxfordshire) reported <1mm of rainfall up to the 19th. This very warm and dry spell brought an arid complexion to the landscape and generated some local concern for the water resources outlook (e.g. in parts of Northern Ireland). Stress on farmers, growers and gardeners was relieved locally by thunderstorms and, more generally, on the 22/23rd when an unusually vigorous summer depression generated rainfall totals of 15-25mm across much of the UK - triggering local flooding and landslides (e.g. in Cornwall); Lough Fea (Northern Ireland) reported 45mm and Buxton 46mm on the following day. The showery nature of much of the rainfall made for imprecise areal assessments but a notable north-south contrast in June rainfall totals was clearly evident. A few localities near the Moray coast reached 300% of average and the above average rainfall in Northern Ireland was particularly welcome. Much of the English Lowlands, however, reported less than half the June average with several coastal pockets being extremely dry (e.g. Portsmouth and Southend). In some regions this arid interlude appreciably increased medium term rainfall deficiencies. The February-June period was the 2nd driest in the last 20 years in parts of the South-West, and, for a few southern catchments (e.g. in the Thames basin), above average rainfall has been registered in only three or four of the 17 months ending with June.
July began in autumnal mode across much of the UK with boisterous, cool, wet and cloudy conditions as a sequence of westerly frontal systems brought high winds and significant pulses of rain, often with thunderstorms in their wake. This very unsettled interlude culminated on the 7th when a particularly vigorous depression moved north across the UK. Daily rainfall totals exceeded 15mm over wide areas and convective activity generated some extreme storm totals: Wittering (Cambs) reported a remarkable 107.4 mm in 19 hours on the 7/8th; an event with a return period exceeding 100 years. Thereafter, thunderstorms remained common (Scampton in Lincolnshire reported 28.6mm in an hour on the 22nd) but rainfall totals were modest at the regional scale and many areas registered <5mm over the final three weeks of the month. July rainfall totals showed an unusual consistency across much of the country (mostly in the 40-70mm range) - this translates into well above average rainfall across much of eastern England but generally below average throughout most of the rest of the UK. Parts of eastern and northern Scotland were particularly dry as were catchments to the south of Lough Neagh in Northern Ireland. Regional rainfall totals for the January-July period were all relatively close to the long term average but some short term deficiencies were notable (e.g. May-July for parts of Wales). Many regions had 10-15% deficiencies over the period since July 2003; in this timeframe the Tay and South West regions registered their 2nd and 3rd lowest rainfalls in series from 1960.
Many new local and catchment rainfall records were established (particularly for high intensity events) when a combination of humid sub-tropical air masses, slow-moving frontal systems and several hurricane remnants made for exceptional precipitation conditions. Much of the precipitation was convective and downpours of near-tropical intensity affected many parts of the country (their impact exacerbated in some cases by hail - a 45mm diameter hailstone was reported at Bracknell on the 5th). Convective storms produced many notable precipitation totals including: 42mm in 38 minutes at High Wycombe (3rd) and an unconfirmed 67mm in 45 minutes near Huddersfield (12th) and a slow-moving front generated exceptional storm totals on the 9/10th. Many areas exceeded 50mm with Skipton registering 96mm in 36 hours and 24hr totals of 73mm (Wheatley, Oxen), 77mm (Sheffield) and 91mm (Wittering, Cambs). In the lower Trent basin a single raingauge reported an exceptional 6-hour total of 86mm. However, the most outstanding August event was a 200mm storm total in around 4 hours at Otterham, north Cornwall on the 16th (return period estimate >>1000 years). Rainfall accumulations were also exceptional over much longer timespans - in Dumfries and Galloway, Boreland recorded a 16-day total of 248mm (RP: > 200 years) and many localities reported record August totals (e.g. Wittering in an 80-year series). For the UK, the rainfall was the highest since 1956; only 1912 has been appreciably wetter in the 105- year national series. Much of eastern Britain reported more than twice the monthly average rainfall and totals for many gauged catchments were amongst the three highest on record for any month. By contrast, a few areas reported monthly totals of <70% (e.g. the north-eastern tip of Scotland, parts of Fermanagh). Such localities aside, the abundant August rainfall contributed to the 2nd wettest summer (June-August) in 47 years for the UK; rainfall totals were well above average in all regions and longer term deficiencies (e.g. from February 2003) were substantially reduced.
In contrast to much of August, Indian Summer conditions characterised early September with and predominately anticyclonic synoptic patterns and exceptional high temperatures characterising the first nine days. During this period precipitation was restricted to fog- drip throughout much of the English Lowlands. Thereafter, incursions of low pressure systems were more common - particularly in northern Britain where frontal rainfall produced some notable storm totals (e.g. Lusa 51mm on the 14th, Sloy 77mm on the 20th, Capel Curig, 56mm in 12 hrs - also on the 20th), and many catchments in Northern Ireland registered 15-25mm on the 29/30th. The preferred tracks of frontal systems were clearly reflected in the September rainfall totals. Above average rainfall was reported for the uplands of western Britain with parts of the Scottish Highlands reaching twice the average. By contrast, low-lying eastern and southern catchments were much drier with large areas of eastern Britain registering less than half the 1961-90 average; a few, mostly coastal, districts (e.g. in Kent) recording less than 30%. Rainfall throughout the summer half-year (April-September) was erratic but all regional totals exceeded the average. Since 1968, the total for Anglian region has been appreciably exceeded only in 2000 - and for some catchments it was the 7th above average summer half-year in the last eight. The summer half-year total only marginally exceeded the average for the Southern region where, for some localities (e.g. Havant), five of the six months were below average. Appreciable long term deficiencies remained (e.g. in the South West from Jan 2003) but accumulated rainfall totals for the first nine months of 2004 were close to, or above, average for all regions.
October was a very cyclonic month with an almost unbroken sequence of vigorous frontal systems producing significant pulses of frontal rainfall. The more notable rainfall totals included 48mm at Lusa (Skye) on the 5th and 24-hr totals of 91mm at Llansadwarn (Anglesey) on the 22/23rd and 78mm at Capel Curig (North Wales), the latter contributing to an exceptional 9-day total of 250mm. October rainfall totals were modestly below average in parts of northern and western Scotland (Allnabad, Highland Region reported 80%) and Northern Ireland (e.g. parts of the Sperrin Mountains) but elsewhere totals generally exceeded the average by a substantial margin. Large parts of eastern and central southern Britain reported more than twice the average and Leuchars (Fife) exceeded 300%. For England and Wales it was the 3rd wettest October in the last 37 years, adding to a cluster of recent wet Octobers. More significantly, the July-October period was the 3rd wettest since 1927 (2000 was similar); in this timeframe much of eastern Britain has been exceptionally wet. Unsurprisingly, rainfall accumulations for the May-October period were well above average in all regions and, for the year to the end of October. Northern Ireland and the Western Isles aside, most regional anomalies in this timeframe exceeded 15% - sufficient to eliminate, or greatly reduce, the large regional rainfall deficiencies built up through the 2003 drought.
Despite a cold snap in mid-month, November was generally mild and cloudy. The damp complexion to the weather (fog and drizzle were common) provided a misleading perception; significant storm events were rare, being largely confined to mid-month in many regions. On the 18th, a 33mm rainfall total was recorded at Grimsbury (Oxon) and significant snowfall was reported as far south as East Anglia. Three days later an active frontal system produced 2-day totals of >50mm in parts of the Western Highlands. Thereafter, November precipitation was largely limited to fog-drip in many areas, and the dry spell continued into December. Rainfall totals of only around 5mm were recorded in parts of central southern Britain over the 21 days from the 21st November. November rainfall totals modestly exceeded the average in parts of western Scotland and in a few parts of central England (e.g. Woburn, Bedfordshire.) but most index raingauges registered only 40-80% of average; the lowest totals clustered in north-east England, and in a zone from Cornwall to Sussex. The UK total of 75mm ranks as the lowest since 1993. Nationally, monthly rainfall totals have alternated between below and above average for the last nine months but in some regions there has been less counterbalancing; autumn (September-November) rainfall totals were particularly low in Southern Region. All regional rainfall accumulations are above average in the June-Nov timeframe and for the January-November period only Southern Region and Northern Ireland have below average totals.
December began with high pressure - which dominated the latter half of November - still acting as the most influential synoptic feature. The associated very dry spell extended to 25-30 days in much of eastern Britain. A vigorous frontal system on the 14th proved pivotal - bringing significant rainfall to much of Britain (a 75mm daily total was reported from Lussa, Kintyre) and heralding a sequence of deep Atlantic depressions; importantly, however, most followed tracks relatively remote from southern England. A cold snap was associated with significant snowfall (as far south as Dorset) around Christmas. December rainfall totals reflected the dominant synoptic patterns - with rain-shadow effects particularly influential in the east. In parts of the Scottish Highlands, precipitation totals approached 200% of the monthly mean, some western catchments in Wales and Northern Ireland were also notably wet. By contrast, much of eastern Britain reported less than half the average rainfall with December totals of <30% in parts of the Midlands. More significantly, England and Wales registered its third lowest November-December rainfall since 1953 and regional rainfall deficiencies in this timeframe were very substantial across much of the UK. The dry end to 2004 was especially notable in a zone from Kent to Northumbria; in the south these deficiencies continued to build well into January 2005. January-December rainfall totals testified to a notably wet year for Scotland as a whole whilst rainfall totals for Northern Ireland and England and Wales were near average. Although most regions of England reported above average rainfall, its distribution through the year was unfavourable in relation to the water resources outlook.