August 2017


Period: From August 2017      Issued on 10.08.2017 using data to the end of July 2017

Summary

The one month outlook is for river flows to be normal to above normal across much of northern and western Britain, with above-normal groundwater levels in some northern areas. In south-east England and parts of central England, river flows and groundwater levels are likely to be normal to below normal, with notably low levels in some areas of the southern Chalk. The three month outlook is for a broadly similar situation to continue, but with a tendency for more river flows and groundwater levels to enter the normal range.

Rainfall

Rainfall during July was above average for much of the UK, while parts of northern Britain and large areas of southern England were exceptionally wet, with over 170% of the July average. Northern Scotland saw below-average rainfall.

The Met Office 3-month Outlook issued on 20th July indicated that for August the chances of above- and below-average precipitation are well balanced. For August-September-October below-average precipitation is slightly more probable than above-average.

The probability that UK precipitation for August-September-October 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 these categories is around 20% (the 1981-2010 probability for each of these categories is 20%).

River flows

For most of western and northern Britain, July river flows were in the normal range or above normal. Flows in much of southern Britain were in the normal range, except for parts of central England and the Welsh borders where flows were below normal.

Following a wet July, the one month outlook is for normal to above normal flows across most of northern and western Britain (with normal flows most likely in the far north of Scotland). While July was also very wet in some central and southern areas, the outlook is for normal to below normal August flows, with below normal flows more likely in groundwater-fed rivers. The three month outlook is similar, and whilst some groundwater-fed catchments may return to the normal range, there is less confidence for the more responsive catchments in the north and west. 

Groundwater

Across the Chalk outcrop, July groundwater levels were below normal or notably low. In other aquifers, groundwater levels were generally normal or below normal except in some northern boreholes where levels were above normal or exceptionally high.

As expected for the summer, the one month outlook is for this situation to persist regardless of August rainfall patterns, as groundwater levels continue to recede. The three month outlook is broadly similar, but levels in the central Chalk may return to the normal range, while notably low levels are likely to persist into autumn in parts of the chalk in the south-east. Over this period, autumn rainfall will become influential in determining the long-term outlook.

Further information - August 2017

Comprehensive further information that supports the production of the Hydrological Outlook UK is available here.