2002 regional rainfall totals for the UK, together with corresponding percentages of the 1961- 90 average are shown on Figure 1; corresponding monthly and half-yearly figures are given in Table 1. In all regions apart from northern Scotland, rainfall exceeded the average - by a notable margin in many cases. England & Wales recorded its third wettest year, after 2000 and 1960, since 1903. Scotland was less outstanding but still 16th wettest in the same timeframe and, more notably, the Northern Ireland rainfall total was almost 50 mm greater than the previous annual maximum. For the UK as a whole rainfall in 2002 was around 15% above average, the winter, summer and autumn each being well above average. Unusually, rainfall exceeded 120% of the 1961-90 average in five separate months - February was exceptionally wet. September was the only notably dry month at the national scale and apart from catchments in north west-Scotland (and the islands) no extended rainfall deficiencies developed.
In climatic terms the most notable feature of the rainfall distribution during 2002 was the unusual tracks followed by most rain-bearing frontal systems. As a consequence of synoptic patterns which for lengthy periods favoured tracks across southern Britain parts of southern England registered October-December rainfall totals which approached the record figures established in 2000. Over the same timespan rainfall deficiencies in western and northern Scotland increased briskly. Following the second wettest January-July period in at least 40 years, the Highland region recorded five successive months with well below average rainfall. Over the August-December period precipitation was only around half the long term average; a remarkable deficiency in this part of the UK - the total was around 100 mm less than the previous minimum for the Highland region in a series from 1961. Modest late summer/early autumn rainfall deficiencies were common across much of the country but these were rapidly made-up during an exceptional wet period from the second week of October. For England and Wales, the October-December rainfall was the third highest (after 2000 and 1929) in a series from 1766 - see Figure 2.
2002 began with high pressure dominating synoptic patterns; correspondingly precipitation was very limited and the sustained low temperatures resulted in frozen catchment conditions over wide areas. Following low rainfall totals in November and December 2001, winter rainfall deficiencies began to develop in much of southern Britain. However, synoptic patterns changed around mid-month allowing a mild westerly airflow to feed a succession of active frontal systems across the UK. As a result January rainfall totals in most western regions were well above average; by contrast some sheltered eastern catchments reported less than 60%.
As the cyclonic pattern continued through most of February many western areas experienced a number of damaging storms. A particularly active depression produced notable rainfall totals on the 1st - approximately 75 mm was reported from Shap (Cumbria) - and regular pulses of rain continued through the month. Over a very unsettled six-week period 522 mm was recorded at Bala (north Wales); this is the equivalent of around four months average winter rainfall and established a new 40-day maximum rainfall accumulation for the site. For the UK as a whole, February 2003 was the third wettest in a series from 1900. Nonetheless, the counterbalancing effect of the dry early winter meant that regional rainfall totals for December-February were mostly well within the normal range.
March was windy but mild, with notable rainfall early in the month; a 24-hr total of 93 mm was reported for Sloy in the western Highlands on the 6th. Most of the frontal systems which crossed the country followed tracks remote from southern England where, in some central areas, fog-drip provided the only contribution to precipitation totals over periods of up to three weeks (extending into April). Northern Ireland registered its 7th successive March with below average rainfall. Notwithstanding substantial month-on-month variability, winter-half year rainfall totals were close to, or above, average in all regions - ensuring an encouraging water resources outlook.
April was an exceptionally mild and sunny month in most regions, with large spatial variations in rainfall amounts. The 100% rainfall isopleth broadly partitioned Britain between the wetter west, where some catchments reported >150% of average and the much drier east. In some areas a short but intense drought - at an important time for the farming community - was terminated by widespread rainfall on the 26th; in some central areas less than 5 mm had been recorded over the previous seven weeks. The late-April rainfall was agriculturally very useful but too late to be hydrologically effective in eastern England where the dry April soils signalled the end of the 2001/02 recharge season.
In May a brief heat-wave in mid-month was more than counterbalanced by longer autumnal episodes during which many localities experienced a wide variety of precipitation types: rain, sleet, snow, hail and fog-drip. Notable storm totals (>50 mm) were reported for Dawlish (Devon) and parts of County Down on 16/17th. May rainfall totals exhibited large spatial variations - a reflection of the showery and thundery nature of much of the rainfall, but most exposed western hills had a notably wet month. For the UK it was the second wettest May since 1986. Northern Ireland was particularly wet; rainfall was around 90% above the May average and contributed to the highest January-May rainfall total in a series from 1900.
Low pressure continued to dominate synoptic patterns in June - across northern regions especially. Scotland and Northern Ireland were very wet but June rainfall totals fell below 70% in parts of England where many lowland catchments were very dry after the initial week. For the UK as a whole, the combined May and June rainfall was the second highest since 1969. In Northern Ireland the wet phase continued; the May-June rainfall was the highest on record.
July was an exceptional month with large spatial and temporal variations in rainfall, lengthy dry spells in central England, and outstanding local storm rainfall totals across a range of timeframes. Approaching month-end the breakdown of a brief heat-wave triggered violent thunderstorms in many areas. On the 30th, 26.2 mm fell in 15 minutes at Kirklees (Yorks), 103 mm was reported in around 6 hrs at Charnwood Forest (Leics). The most severe local flooding was in Glasgow - triggered by a six-hour total of 61 mm (including 38 mm in a hour and a maximum intensity of 94.5 mm/hr). A 3-hour total of 49 mm at Leuchars (Fife) contributed to the wettest July in an 80-year rainfall series. Notwithstanding some dry interludes, July rainfall totals were well above average in most regions and the unsettled complexion to the late-spring/early summer weather patterns is reflected in the May-July rainfall - the wettest such period since 1958 for the UK (but 1968 and 1997 were only marginally drier). Exceptionally wet conditions extended across a broader timespan in Scotland and Northern Ireland which, respectively, reported their second highest and highest rainfall on record for the January-July period.
The extremely wet spell continued into August; for the rain-day ending on the 1st, Fylingdales (Yorks) registered 114.6 mm and totals were outstanding throughout most of North-East England. Exceptional rainfall totals characterised wide areas for the week ending on the 5th. More locally, Olney (Bucks) reported 63 mm on the 6th, an exceptional figure for a lowland site. From the 13th, a rare (during the spring and summer of 2002) north-eastward extension of the Azores high pressure cell produced very dry and warm conditions. Northern Ireland recorded its driest August since 1995. The summer (June-August) rainfall total was appreciably above average for the UK as a whole and some of the driest (on average) catchments in eastern England reported their fifth summer in the last six with above average rainfall.
September was a very mild, sunny and dry month in most regions as anticyclonic conditions persisted in most regions. Most catchments reported lengthy dry sequences - but punctuated locally by some notably intense storm events, commonly associated with thunderstorms. On the 7/8th torrential rainfall (>90 mm, including 61 mm in 4 hours) caused severe flooding in Inverness (Highland). The following day Swanage (Dorset) reported a very exceptional 121.4 mm (including 71 mm in two hours) and rainfall totals exceeded 20 mm over much of England and Wales. This widespread event heralded an extended dry spell, and many areas reported 27 or more days without significant rain in September. Scotland and Northern Ireland registered their driest and second driest September respectively in the last 30 years. More significantly, only in 1972 has the combined August/September rainfall been appreciably lower for the UK.
Rainfall deficiencies continued to build in early October - sequences of days without significant rainfall extended to 30 or more in parts of central England. However, from the 9th active frontal systems again tracked across the British Isles, heralding a very unsettled episode with damaging gales towards month end. The passage of several sequences of vigorous depressions produced exceptional 2-5 day rainfall totals: 120 mm at Dunkeswell (Devon) on the 11-15th; 90 mm in parts of the Grampian Region (22-23rd) and >130 mm in the Mourne Mts, 20-22nd, heralding an outstandingly wet 7-day period in northern Ireland. Parts of northern and western Scotland - to the north of the favoured frontal tracks - had a dry month but most regions reported rainfall totals >150% of average. The third notably wet October in succession produced a dramatic change in the hydrological outlook, flood risk was significant in many areas by month end.
Continuing the synoptic theme established in October, November was a mild but stormy month as a succession of vigorous Atlantic low pressure systems crossed the British Isles. Dry days were rare - a few localities reported none (e.g. in parts of Northern Ireland) - and some 2-3 day rainfall accumulations were very exceptional. From the 15-17th orographic enhancement contributed to a remarkable 240 mm total reported for Mulden (near Elgin), equivalent to around a quarter of the annual average, triggering severe flooding in the Grampian Region. Some exposed catchments in south-west Britain recorded more than 40% of average annual rainfall over the seven weeks from Oct 13th and the monthly total reached three times the October average for some locations in central southern England. At Wallingford (Oxon), November was among the four or five wettest months in the last 50 years. Consequently, autumn (September-November) rainfall totals were well above average in all regions apart from western and northern Scotland - in parts of the latter, rainfall was only a little above 50% of the 1961-90 average.
Apart from a calm interlude in mid month, resulting from a westerly extension of the Scandinavian high, active frontal systems were again very common in December. However the low pressure systems generally followed an even more southerly track. Much of Scotland was relatively dry, the north-west remarkably so - extending an exceptional rainfall deficiency which began in the late summer. The hydrological magnitude of this drought was emphasised by the December rainfall in some catchments in south-east England which reported monthly totals five times greater than that for some catchments in north-west Scotland - a rare circumstance. December rainfall totals were very high throughout most of southern Britain and a sequence of depressions over the final week, producing rainfall totals of 50-100 mm over wide areas and triggering widespread flooding which continued into 2003.