The provisional annual rainfall total for the UK in 1998 is 1259 mm, 117% of the 1961-90 average. Most regions received substantially above average rainfall - reflected in the provisional totals for England and Wales (1026 mm - 115%), Scotland (1718 mm - 120%) and Northern Ireland (1179mm - 111%). On the basis of provisional data Great Britain registered its third wettest year this century and Scotland its third wettest in a series from 1869 (but 1990 and 1992 were both wetter). Some caution is necessary in interpreting these rankings, the final rainfall figures may differ appreciably from the provisional estimates and artifacts in both the Great Britain and, in particular, the Scottish rainfall series mean that recent totals may be overestimated relative to earlier annual figures.
The 1998 regional rainfall totals varied between 114% and 134% of the 1961-90 average (see Figure 1). Almost all major catchments received above average rainfall with only sheltered parts of south Devon/Dorset having less than the annual mean, although rainfall totals were only marginally above average in the Fort William area. Throughout the driest parts of the country - the English lowlands - rainfall totals were typically 20% or more above average. The overall area registering annual rainfall totals of less than 600 mm was the second lowest in the last 30 years.
In percentage terms the regional rainfall totals show considerable spatial coherence but temporal variations in rainfall through the year were considerable. February, May and August were relatively dry whereas April (see below), June and October were notably wet. February 1998 was dry throughout most of England and Wales - the fourth driest February in the last 33 years - with the Southern and Anglian regions receiving less than 20% of the 1961-90 mean. By contrast Sconser on the Isle of Skye logged a monthly rainfall total of 646 mm, greater than the average annual rainfall over most of eastern England. For England and Wales, April was the wettest since 1818, some districts - mostly in the Midlands - recording more than three times the monthly average. On the 9th, a frontal system aligned along a broad swathe from The Black Mountains (South Wales) to the Wash became very slow moving and many catchments received the equivalent of an average month’s rainfall (45-70 mm) in around 10 hours; maximum 48-hour totals of 90 mm in Pershore and 97 mm in Peterborough were recorded. Extensive flooding ensued (see Runoff).
May was the equal 12th driest this century for England and Wales; parts of eastern Wales and Essex registered less than a quarter of the monthly average rainfall. Westerly airflows returned to dominate weather patterns in June which for England and Wales was the third wettest in the last 120 years; some western locations e.g. Valley (Anglesey) and Plymouth (Devon) established new rainfall maxima for the month. Well above average rainfall totals were recorded for most catchments in July also; Scotland had its wettest July for 10 years. August provided a notably dry interlude in England with some southern districts, which escaped the thunderstorms, receiving less than 10 mm. In September, a sequence of vigorous frontal systems crossed southern Britain producing double the average September rainfall in some parts of the English lowlands, much of western Scotland, by contrast was notably dry. October was very wet throughout the UK. Treherbert, at the head of the Rhondda valley in South Wales, recorded a monthly rainfall total of 550 mm, its second highest rainfall there for any month in the past 30 years. Serious flooding occurred in South Wales and the Severn Basin.
November was also unsettled and the provisional autumn rainfall total for Great Britain was the highest (along with 1992) since 1984. December rainfall totals were a little below average in most parts of England and Wales but, with soils remaining close to saturation, the seasonal recovery in river flows and groundwater levels was maintained. One consequence was that stocks in almost all strategic reservoirs were near capacity entering 1999.