April 2015


Period: From April 2015      Issued on 15.04.2015 using data to the end of March

Summary

The outlook for April suggests normal river flows are likely to predominate across the UK. While normal flows are the most likely outcome, in parts of Northern Ireland and Scotland there is an increased probability of above normal flows, whereas there is a increased probability of below normal flows  in small catchment draining to the east coast of Scotland and England, in Wessex and parts of central England. The outlook for the next three months is for flows to be in the normal range throughout the UK. Groundwater levels in April are likely to reflect the pattern observed in March, but over the three month timeframe below-normal levels are more prevalent and notably low levels are likely in some parts of the Chalk aquifer. 

Rainfall

The latest predictions for UK-mean precipitation favour near- to above-average rainfall in April. For April-May-June, there is a slight shift away from climatology towards above-average precipitation but there is a wide spread of possible outcomes. The probability that UK precipitation for April-May-June will fall into the driest of five equal categories is around 20% and the probability that it will fall into the wettest of the five categories is 25% (the 1981-2010 probability for each of these categories is 20%).

River flows

River flows in March were in the normal range across almost all of England and Wales, with below normal flows in a few localities. Flows in central and western Scotland and northern parts of Northern Ireland were above normal, appreciably so in some cases, while some small eastern Scottish catchments saw below normal flows. The one month outlook is for a similar picture, especially given the wet start to April in these areas. Below normal flows are likely in some areas, such as in in Wessex, parts of central England and north-east Scotland. For the three month outlook, the most likely outcome across the country is for normal flows, although there is an increased possibility of lower than average flows in groundwater-dominated catchments in southern England.

Groundwater

In March, normal groundwater levels were widespread across the Chalk, but with below-normal levels in north-east England and above-normal levels in the far south-east. Levels were variable in other aquifers, with both above- and below-normal levels in the Permo-Triassic of central England. With recessions established in most aquifers, groundwater levels over one to three months are relatively insensitive to  rainfall, with significant recharge unlikely unless rainfall is exceptional. The one month outlook suggests significant areas of the Chalk aquifer will see below normal levels and, except in the far south-east, the three month outlook suggests a predominance of below normal levels, with an increased probability of some notably low levels by mid-summer. Levels in the Permo-Triassic of northern England and southern Scotland are likely to remain normal or above.

Further information - April 2015

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