October was a mild month with a sub-tropical airflow re-introducing Indian Summer conditions over the last 10 days in south Britain especially. Rainfall for Scotland was modestly above average with very wet conditions in some eastern catchments triggering flooding late in the month. By contrast, most southern regions of the UK were relatively dry, notably so in parts of the English Lowlands where accumulated rainfall deficiencies since February are substantial. Some brisk recoveries in reservoir stocks were reported (e.g. for parts of northern England) and, although at their lowest for two years, overall stocks for England & Wales are well above the late autumn average. However, seasonally low stocks characterise some southern impoundments (e.g. Bewl and Ardingly). Seasonal recoveries in runoff rates became established in many northern and western catchments over the second half of October but modest flows typified many rivers in eastern, southern and central England where extended recessions left flows close to monthly minima in a few areas. Broadly the largest medium-term rainfall deficiencies coincide with the outcrop areas of the Chalk (and some minor aquifers) where continuing recessions produced notably low groundwater levels in some southern outcrops. In such areas the change to much more cyclonic weather patterns at month end was especially welcome.
Westerly airflows, often dominant in October, were relatively infrequent this year although northern and western areas experienced gales on a number of occasions. Anticyclonic conditions in mid-month brought autumnal mist and drizzle and, over the final third of the month, very warm sub-tropical air drawn north on the flank of continental high pressure created balmy and warm late-October weather. In Scotland, a very-slow moving frontal system brought prolonged rainfall to parts of the north-east on the 20th heralding an exceptionally wet interlude: Waterside (Esk catchment) reported 90mm on the 21st, and a 5-day total of 182mm; several other raingauges recorded >150mm. For October as a whole, the highest rainfall anomalies were found in eastern Scotland with some areas (e.g. Aberdeen) exceeding 200%. In England, rainfall totals showed large spatial variations with above average rainfall in some coastal localities contrasting with <50% in a few central localities (including parts of London). Across large parts of the English Lowlands, only July has registered above average rainfall in the last eight months. Correspondingly, accumulated totals are relatively depressed - the provisional March-October total for Southern Region was the 5th lowest in 80 years. By contrast, Scotland registered its wettest May-October in 55 years with the Highland and North East regions being exceptionally wet.
Throughout almost the entire country the sustained early autumn recessions continued into October, leaving river flows well below the seasonal average. In Northern Ireland runoff rates were especially depressed during the second week (e.g. in the Faughan) but flow recoveries gathered momentum in south-western Britain and then, more dramatically, in Scotland from mid- month. Notably high flows were recorded on 21-23rd in eastern Scotland: on the Don both the Alford and Parkhill gauging stations registered their 5th highest flow on record whilst the Feugh reported its 2nd highest. The associated floodplain inundation, and surface flooding, caused severe transport disruption (including closure of the Aberdeen-Dundee rail link). In much of southern and eastern Britain however flows continued to decline. Flows in the Lud (Lincs) fell to their lowest since the summer of 1997 and notably low flows characterised many Anglian rivers (including the Colne and Waveney). Estimated October outflows for England & Wales were the third lowest in over 30 years and the great majority of index rivers recorded below average monthly runoff, many registering <50%; for the Little Ouse, October runoff was the 2nd lowest in a series from 1968. Generally, accumulated runoff totals, are well below average in the English Lowlands but exceptionally high in much of Scotland, the east particularly.
Soils were close to saturation at the end of October in much of western and northern Britain - contributing to an enhanced flood risk in parts of eastern Scotland - but remained seasonally dry in most major aquifer outcrop areas. Across much of the southern Chalk soil moisture deficits were around twice the late-October average and in a few areas (e.g. East Sussex) late-October soils were the driest for 30 years. Correspondingly, late-summer and autumn groundwater level recessions have been steep in part of the southern Chalk where Chilgrove is approaching its natural base level. With meagre infiltration in October, commonly <30% of average, groundwater levels are well below average across much of the South East, and extend to a few western wells (e.g. Tilshead). Levels in index wells penetrating the limestone aquifers are mostly below average but well above drought minima whilst near-average autumn levels are found in most Permo-Triassic sandstones aquifer units; groundwater resources are particularly healthy in the most northerly outcrop areas. The wet beginning to November, some parts of the South-East reported >60mm of rainfall in the first week, is particularly timely. An unsettled outlook is also encouraging but much will depend on the actual tracks followed by the low pressure systems.