December 2015


Period: From December 2015      Issued on 11.12.2015 using data to the end of November 2015

Summary

The one-month outlook is for December flows to be above normal across most of northern and western Britain, with an increased likelihood of exceptional flows in some regions. These projections reflect the exceptionally wet November in much of northern Britain. In actuality, early December has already witnessed exceptional rainfall and flooding in northern England and parts of Scotland, so it is highly likely that total flows for December will be exceptional. With meteorological projections favouring wetter-than-average conditions over the next three months, there is an increased likelihood of above normal winter flows in many northern and western areas, and high groundwater levels are also likely in aquifers in these areas. In the south and east of England, winter river flows and groundwater levels are largely expected to be normal or above, although below normal levels are likely to persist in some eastern areas.

Note: Up-to-date flood warnings are available from the websites of the Environment Agency, Natural Resources Wales and Scottish Environment Protection Agency.

Rainfall

For December and December-January-February as a whole above-average precipitation is more probable than below-average. The probability that UK-average precipitation for December-January-February will fall into the driest of five equal categories is between 10% and 15% and the probability that it will fall into the wettest of five categories is 25% (the 1981-2010 probability for each of these categories is 20%).

River flows

November river flows were mostly in the normal range in southern and eastern England and in the far north of Scotland, with below normal flows in a few catchments in the latter. Elsewhere in northern and western Britain, river flows were above normal, with exceptionally high flows in northern England and north Wales. The one month outlook is for a similar picture: river flows are likely to be above normal across most of northern and western Britain and there is an increased likelihood of exceptional flows in many places. In south-east England, normal to above normal flows are expected while in north-east Scotland flows are likely to be normal. The three month outlook is for a continuation of above normal flows in some northern and western regions, but in others (including Wales and much of Scotland) flows are more likely to return to the normal range. In south-east England flows are likely to be normal to above normal. 

Groundwater

In the Chalk, November levels were mostly in the normal range or below, with below normal levels mainly in eastern England. In other aquifers levels were mostly normal to above normal.  The one month outlook is for a continuation of this situation, with mostly normal levels in the southern Chalk and normal to below levels further east, and above normal levels in parts of the Permo-Triassic sandstone. The three month outlook suggests a mixed pattern for the Chalk, with below normal levels in some eastern areas contrasting with above normal levels for the South Downs. Elsewhere normal to above normal levels are likely and parts of the Permo-Trassic sandstone in the north west may see exceptionally high levels. These increases reflect the wetter-than-average rainfall projections and the latter looks increasingly likely given early December rainfall in northwest England. However it should be noted that high levels in the Permo-Triassic sandstone do not play a significant role in flooding. 

Further information - December 2015

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