Following an exceptionally dry October across the majority of the UK, the outlook for November is for river flows to be below normal to normal across the UK, with below normal flows more likely in the south and east. Below normal to normal flows are likely to persist across the south and east of the UK over the next three to six months. Groundwater levels are expected to be within the normal range, except in areas of the southern Chalk which are likely to be below normal over the next three months.
Rainfall over October was unseasonably low. Western and southern parts of the UK saw rainfall totals from less than 30% to 50% of the 1971-2000 average, whilst localised areas in coastal Norfolk, Northumberland and north-eastern Scotland saw above average rainfall. October has been the fourth consecutive month of drier than average rainfall totals across the UK. South-east England has seen the least rainfall over this period.
For November, below-average precipitation is more probable than above-average values. For the period November-December-January as a whole, the chances of below-average precipitation are also higher than those of above-average values. The probability that UK precipitation for November-December-January will fall into the driest of five equal categories is between 20 and 25% and the probability that it will fall into the wettest of the five categories is around 15% (the 1981-2010 probability for each of these categories is 20%).
Reflecting the dry nature of October’s rainfall, river flows in western parts of the UK have been below normal to exceptionally low, with several rivers exhibiting record low flows for the month. Normal to below normal flows were recorded across eastern parts of the UK.
The outlook for November indicates that river flows in the northern and western parts of the UK are likely to be below normal to normal. In southern and eastern parts of the UK, a combination of slower streamflow response to rainfall due to groundwater influence, as well as high soil moisture deficits, contribute to a longer term low river flow outlook. Here, flows are more likely to be below normal than normal over the next one to three months, with a continuation of a normal to below normal outlook over the next three to six months.
Groundwater levels generally continued receding into October, delaying the usual recharge of aquifers at this time of year. The northern Permo-Triassic sandstone aquifers returned to normal levels after a prolonged period of above average levels following winter 2015/2016. Groundwater levels for October were generally within the normal range, with a few southern boreholes recording below normal levels.
The outlook for November to January is for groundwater levels to be within the normal range, though parts of the southern Chalk aquifer are likely to be below normal over the next three months.