January 2016


Period: From January 2016      Issued on 12.01.2016 using data to the end of December 2015

Summary

The one-month outlook is for January river flows to be above normal across most of northern and western Britain, with flows likely to be much higher than the normal range in some areas, particularly in north-east Britain where flows may be exceptional (major flooding has already occurred in early January in eastern Scotland). In south-east England, flows are likely to be normal to above normal. January groundwater levels are also likely to be normal to above normal. These expectations are largely a result of the very wet start to January, which has seen exceptional rainfall in many areas; much of north-east Britain saw more than the January average in the first week. Meteorological projections do not show any strong signal for wet or dry conditions over the next three months, implying normal river flows and groundwater levels will predominate, although the wet start to 2016 may result in seasonally high levels in some aquifers.

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

Rainfall

Based on projections released by the Met Office on 27 December. For January and for January-February-March, both above- and below-average precipitation are equally probable. The probability that UK-average precipitation for January-February-March will fall into the driest of five equal categories is around 20% and the probability that it will fall into the wettest of five categories is also around 20% (the 1981-2010 probability for each of these categories is 20%). 

River flows

River flows for December were exceptional across northern and western Britain, with new peak flow records established in many catchments, leading to severe flooding in many areas of northern England and Scotland. In southern and eastern England, December flows were mostly in the normal range. The one-month ahead projections based on the rainfall forecasts detailed above indicate above normal flows in northern and western Britain, and normal flows in south-east England. However, as usual there is a wide range in the rainfall forecasts and the exceptional rainfall witnessed in early January has increased the likelihood of the upper range of forecasts. Given the recent rainfall, it is likely that flows in northern Britain will be substantially above normal, with exceptional flows very likely in parts of north-east Britain that have been wettest. There is also an increased chance of above normal flows in south-east England. The three month outlook is more suggestive of a return to the normal range across the UK; the wet start to January increases the likelihood of flows above the normal range, but this has less influence on the three month outlook.  

Groundwater

December groundwater levels in the Chalk displayed a very mixed pattern, with below normal levels in some boreholes in central southern England and normal or above normal levels elsewhere. In other aquifers levels were normal or above normal, with very high levels in some northern aquifers. Based on early January rainfall, groundwater levels in the next month are likely to be normal or above except in the slower responding parts of the Chalk in central and eastern England. Exceptionally high levels will persist across Permo Triassic aquifers in the north. In the Yorkshire Chalk and in Wessex and along the south coast, levels  may rise to notable or exceptional levels and this may result in localised groundwater flooding. The three month outlook suggests a similar pattern, with normal to above normal groundwater levels prevailing, and a significant chance of notably high or exceptionally high levels in the most responsive aquifers.

Further information - January 2016

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