2003 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. For the UK as a whole, the 2003 rainfall total was around 18% below average with significant deficiencies characterising all regions – typically in the 15-25% range with the greatest anomalies in north-eastern Britain. England and Wales registered its driest year since 1975, Scotland its driest since 1972 whilst Northern Ireland reported its second lowest rainfall (after 2001) in the last 29 years. The distribution of rainfall through the year was also very unusual: January and December were very wet but many localities reported 8 or 9 months with below average rainfall. The very damp start to 2003 continued a wet episode which began in the autumn of 2002. Western Scotland aside, regional rainfall totals for the October 2002-January 2003 period (Figure 2) exceeded the average by a significant margin – helping to ensure that water resources were well placed to withstand the ensuing drought conditions.
The most significant characteristic of the 2003 synoptic patterns over the UK was the relative rarity of rain-bearing frontal systems over the late winter and early spring period, and again during the late-summer and early autumn. The scale of the resulting rainfall deficiencies is illustrated on Figures 3 and 4. Despite considerable late-April rainfall, the February-April total was the lowest for the UK as a whole since 1956 with large parts of the English lowlands reporting only a little over 50% of average rainfall. Even greater deficiencies characterised the August-October period which, for the UK, was the third driest on record. Some areas in central southern England registered less than 40% of average rainfall – such deficiencies correspond to return periods of around 50 years and deficiencies across almost all regions of the UK corresponded to return periods exceeding 20 years. The intensification of the drought well into the autumn resulted in the February-October period being the driest on record for the UK apart from 1921 (in a series from 1900); over this timespan, rainfall deficiencies exceeded 30% over wide areas (Figure 5). The high frequency of Atlantic frontal systems from mid-October until the end of the year was, thus, especially welcome.
January was notable for a very wide range of weather conditions – exceptionally mild interludes punctuating much colder spells with damaging blizzards on occasions. Snow constituted a significant proportion of total precipitation in parts of northern Britain (in eastern Scotland especially) and London had appreciable falls on the 8th and 30th – the latter associated with massive transport disruption. Of most hydrological significance was the continuation into January of a very wet spell during late December 2002. Some localities in central southern England reported the equivalent of 6-8 weeks of average winter rainfall over the 12 days beginning on the 21st December. Widespread rainfall on New Year's Day – Culdrose (Cornwall) reported 48mm in the 24 hours to 18.00hrs – ensured that the flooding, already notable in late December, would become more extensive and protracted. The January precipitation total was near average for the UK but much of eastern England was particularly wet, parts of East Anglia reporting almost twice the January average. However, the relative infrequency of Atlantic frontal systems after the first week resulted in generally below average January rainfall totals in the west – some catchments in Cornwall recorded <60% and longer term rainfall deficiencies – which began in the late summer of 2002 – continued to build in parts of western Scotland and the islands.
Weather conditions during February contrasted with those which typified most of the late autumn and early winter of 2002-03. Damaging blizzards (e.g. on the 3rd) – with substantial snow accumulations – produced considerable transport disruption in Scotland but precipitation totals were influenced more by the preponderance of dry days in mid-month; many areas reported little more than a trace of rain over the fortnight beginning on the 11th. With high pressure dominant, the rainfall total for the UK was the second lowest – for February – in the last 18 years. The low frequency of rain-bearing frontal systems resulted in below average precipitation across much the greater part of the UK. A few localities (e.g. Milford Haven and Morecambe) reported marginally above average February rainfall but most catchments registered between 40% and 70%; parts of eastern Scotland were especially dry. In Scotland, a continuation of a notable longer term rainfall deficiency in the north and west contributed to the second lowest winter (December-February) rainfall total since 1964. To the south, winter rainfall totals for all regions were within the normal range, but above average rainfall again characterised much of the English lowlands – many catchments reported their fifth successive wet winter.
Several vigorous Atlantic frontal systems brought significant rainfall to most areas in early March – many western upland catchments reported notable falls; on the 7/8th, Capel Curig (Gwynedd) registered 111mm in 36 hrs (including 80mm in 12 hrs). However, from the middle of the second week, high pressure dominated synoptic patterns and many areas reported long sequences of days with precipitation restricted to fog-drip. In some parts of southern England (e.g. the Lambourn Valley) no rainfall was recorded over the last 24 days of the month, continuing a relatively arid interlude – extending over nine weeks in some areas – which transformed the hydrological picture across much of the UK. The parched catchment conditions (for the spring) greatly reduced the risk of flooding but also signalled an early end to the aquifer recharge season – in some eastern aquifers particularly. Rainfall totals for March were below average throughout mainland UK. Northern Ireland registered its driest March since 1973 and, in Britain, rainfall deficiencies were generally greatest in the driest regions of the country – some sheltered southern and eastern catchments reported monthly rainfall totals of less than 15mm. The combined February and March rainfall totals were the lowest for 30 years in parts of eastern Scotland, and also notably low in much of eastern England.
Apart from a wet and blustery start, the first three weeks of April were mainly dry, extending a dry spell which started in mid-February. Rainfall totals were especially low over the seven-week period from the 8th March. Some places in north-east England reported less than 5mm of rainfall whilst in Wallingford (Oxon), measurable rain occurred on only four days (totalling a mere 2.6mm). Fortunately, widespread frontal rainfall, beginning on the 21st, reduced the growing risk of forest fires. Nonetheless, regional rainfall totals for April were well below average across the UK – less than 50% in the Western Isles, the seaboard of north-east England, the East Midlands, central London, eastern Kent and south Dorset. Substantial rainfall deficiencies over the Febrary-April period extended across almost all regions of the UK. In this timeframe, the Northumbrian and Anglian regions reported less than 50% of average rainfall, contributing to the lowest February-April rainfall since 1976 for England and Wales, and since 1975 for Scotland.
The episodic weather patterns, which were a feature of much of the 2002-03 period, continued during May. Notable late-winter and spring rainfall deficiencies increased in a number of lowland catchments, but were greatly moderated in most regions as the late-April rainfall heralded a prolonged unsettled spell. Mid-May was especially wet – a daily rainfall total of 52.2mm was reported for Silent Valley (Northern Ireland) on the 15th – and the month ended dramatically with heat-wave conditions and violent thunderstorms with hailstones and localised flash flooding. An especially severe storm – with remarkable surface runoff and debris slides – afflicted Yarrowford and Selkirk (in the Tweed basin) on the 30th. This contributed to the 4th wettest May on record for Scotland in a series from 1869. By contrast, May rainfall totals in a few southern and eastern coastal areas of England fell below 70% of average and spring (March-May) totals were particularly low throughout the English Lowlands (parts of the North-East also). In such areas, a notable drought could be traced back to mid-February; for the Thames basin the February-May rainfall was the second lowest, after 1976, in the last 48 years.
June was generally very warm with lengthy dry spells punctuated by showery or more stormy interludes. Rainfall for the UK as a whole was close to the long term average but its spatial variability was substantial, partly as a result of high temperatures triggering several thundery episodes. On the 1st, a 39mm rainfall total was recorded in an hour at Shepshed (Leics) and 60mm in around 2.5 hours was reported for St Leonards (East Sussex) early on the following day; both storms have return periods > 50 years. Further convective storms on the 22nd were responsible for more than half the total June rainfall in some southern catchments. More significantly, rainfall deficiencies – which had built up since late January in some areas – moderated across much of the country. Nonetheless, February-June rainfall totals were well below average in all regions; in this timeframe, many catchments in a zone from Dorset to Essex reported their second lowest rainfall total (after 1976) since 1962.
July was a very warm month with rainfall modestly above average for the UK as a whole but, as in June, the thundery and showery nature of much of the rainfall made for large local and regional differences in monthly totals. High intensity rainfall events were particularly common in mid-month and towards month end. A storm total of 55mm was recorded at St Athan (South Wales) on the 17th, whilst Newry (Northern Ireland) registered 70mm on the following day. On the 25th, Cardinham (Cornwall) reported 62mm and, at month-end, a remarkably intense storm produced a three-hour total of 54mm at Borgue (Dumfries and Galloway) – its estimated return period exceeds 100 years. During July, most frontal systems approached from the South-West; accordingly, a few localities in Cornwall and South Wales recorded over twice the monthly average rainfall. By contrast, areas in the rain-shadow of the western hills, (and which missed the thunderstorms), were relatively dry – parts of the west Midlands recorded <60% of the July average and some catchments along the eastern seaboard were even drier. Generally, regional rainfall totals for July were in the normal range across England and Wales but, once again, well below average across much of Scotland.
August was an extremely warm month – previous maximum recorded temperatures were eclipsed in many areas during a heat-wave beginning on the 3rd – and exceptionally low rainfall totals characterised most regions. Although the UK's longest absolute drought (73- days in East London in 1893) was not threatened, many notably arid interludes were reported – sequences of 26 or more rainless days being reported in parts of the English Lowlands. A few locally intense storms did occur, (e.g. a remarkable 45mm precipitation total in 10 minutes at Carlton-in-Cleveland, North Yorks on the 10th), and significant rainfall on the 28th prevented existing minimum August rainfall totals being eclipsed in many localities. Nonetheless, August totals were below 20% of average across the greater part of the UK, and less than 10% in many eastern lowland catchments. Large parts of the English Lowlands reported <5mm with only a single millimetre recorded for a few localities adjacent to the Wash. The August 2003 rainfall total was the fourth lowest for the UK in a 104-year record. More significantly, it was the seventh successive month with below average rainfall in some English lowland catchments. For the Thames basin, the February-August rainfall was the third lowest in the last 65 years – 1976 was substantially drier. Deficiencies in this timeframe were also notable in much of northern England and eastern Scotland.
As anticyclonic conditions continued to dominate synoptic patterns, September was another warm, sunny and, in most areas, dry month. A few notable storm events were reported – on the 19th severe damage was caused in the southern Shetlands by an exceptionally intense event and Dover suffered localised flooding on the 27th. Generally however, protracted sequences of dry days contributed to very modest September rainfall totals. Above average September rainfall was confined to a few, mostly upland, pockets whilst much of the UK registered 40-60% of the 1961-90 average with totals below 20% in substantial parts of southern England. England and Wales recorded its second driest August-September period in a series from 1766 and the extremely arid end to the summer half-year substantially increased the rainfall deficiencies that had been building since late January. The February-September rainfall total for the UK is the second lowest, after 1959, in the last 74 years – testifying to a notable and extensive drought which was most severe in parts of north-eastern Britain and the South-East. By the end of September, the estimated return periods for the post-January rainfall deficiency exceeded 20 years over the greater part of the UK.
Significant rainfall during the last week of October provided a welcome break in the drought conditions but rainfall deficiencies again increased considerably over the month. The UK rainfall total for the nine months ending in October 2003 was the lowest since 1921 with a few southern catchments having reported below average rainfall in each of the nine months. Thus, the abundant rainfall across parts of central southern England in the six days to the 2nd November – was particularly welcome; in some areas the 6-day total exceeded that for the preceding 12 weeks. Nonetheless, October rainfall totals were well below average across much of the UK; several monthly minima were established (e.g. Solwaybank, Dumfries and Galloway, reported its lowest October total in a 43-year record). Importantly from a resources perspective, many reservoir gathering grounds (including the Pennines) recorded below half their average October rainfall and for England and Wales as a whole, the February-October total was the second lowest, after 1959, since 1921. At month end the drought still affected much the greater part of the UK – return periods for the nine-month rainfall totals exceeded 50 years over wide areas. There were, however, important regional and local variations; an especially intense drought afflicted parts of the Thames basin – the February to October rainfall for the west London area was the second lowest in a series from 1697.
November was a mild month with large spatial variations in rainfall amounts. Drought severity increased across much of the Midlands and northern Britain where November rainfall was below average. By contrast, the South East was exceptionally wet. Cyclonic conditions dominated during the third week and one particularly slow-moving system generated rainfall totals of 40-80mm across a large part of the English Lowlands (Wisley in Surrey registered 95mm in 96 hrs; a few localities reported more rainfall than over the preceding three months). The, mostly moderate intensity, rainfall was very effective in reducing soil moisture deficits. Further rainfall over the following weekend contributed to November totals of twice the average in parts of the English Lowlands. Nonetheless the February-November rainfall totals for England and Wales and Scotland rank, respectively, third driest in the last 116 years and the lowest since 1955. Entering December, accumulated rainfall deficiencies exceeded 20% in most regions of the UK. The drought remained very extensive but the November rainfall changed its focus – the most severe deficiencies (over 10 months) were now in northern England and eastern Scotland.
Even in southern Britain, a wide range of precipitation types – from fog-drip to snow – were reported during December. However, the very damp complexion to the weather, from mid-month especially, often failed to translate into substantial daily rainfall amounts. Exceptions included a 36mm total on the Isle of Wight on the 1st and 80mm in 18 hrs at Shap Fell in the Lake District (26th); both were very useful storms in a water resources context. Despite the reduction in regional rainfall deficiencies over the latter half of the month, the February-December total for Britain was the third lowest since 1933. The drought remains notable in this timeframe – especially in the North-East where parts of Yorkshire recorded above average rainfall for only two months in 2003 (a distinction shared with parts of the Midlands and central southern England). Although the December rainfall total was only marginally above average for the UK, the nature of the mostly frontal rainfall and the generally wet soil conditions ensured that it was very hydrologically effective – contributing to a very notable improvement in the water resources outlook.