May 2015


Period: From May 2015      Issued on 14.05.2015 using data to the end of April 2015

Summary

The outlook for May suggests normal river flows are likely in northern Britain, and normal to below-normal flows further south. This reflects the notably low April rainfall across England and Wales, with less than half the monthly average received in most areas; however, early May has been very wet in all regions, which decreases the likelihood of very low flows and increases the chances of above-normal flows in the north. The groundwater outlook is for a similar picture to April, with mostly normal and below-normal levels. Over the next three months, flows and groundwater levels are likely to be normal or below normal across the UK, with an increased likelihood of notably low groundwater levels in some areas.

Rainfall

Latest predictions for UK precipitation favour a slight shift towards above-average rainfall for both May and May-June-July as a whole. The probability that UK precipitation for May-June-July 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 25% (the 1981-2010 probability for each of these categories is 20%).

River flows

With the exception of several catchments in Scotland and Northern Ireland, River flows in April were normal or below, with below normal flows (which were notably low in some cases) largely concentrated in southern England, eastern Scotland and a few catchments in central England and Wales. The one month outlook is for normal- to below-normal flows across much of England and Wales. In northern England and Scotland normal flows are the most likely outcome, although below normal flows may persist in north-east Scotland. Above normal flows are unlikely based on the forecasts, although given the unsettled start to May the chance of above normal flows for northern Britain has increased. The three month outlook is suggestive of normal to below normal flows across the majority of the UK, with the likelihood of below normal flows increasing relative to the one month outlook. 

Groundwater

Normal groundwater levels were widespread across the Chalk in April, but with below-normal levels in north-east England and Wessex contrasting with above-normal levels at a few boreholes in the south-east. Groundwater levels were variable in other aquifers, with above-normal levels in parts of the Permo-Triassic sandstone. With evapotranspiration increasing and seasonal recessions generally well established, the outlook for both one and three months is for a broadly similar situation to persist. Levels in most aquifers are likely to be normal or below, with above-normal levels largely confined to some central and northern parts of the Permo-Triassic sandstone aquifer. Below normal levels are likely over the next three months in western and north-east England, with the possibility of notably low levels in some localities. 

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Further information - May 2015

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