June 2013


Summary

In the absence of notably high or low rainfall, river flows in June are very likely to be in the normal range, for the time of year, across most of the UK. Across all aquifer areas, groundwater levels are very likely to be above normal (significantly so in some areas) over the next  months. The water resources outlook for the summer is therefore very favourable.

Rainfall

For June, there is a large degree of uncertainty, but on balance above-average rainfall is more likely than below-average. For the June-July-August period as a whole above-average rainfall is also more probable than below-average rainfall. There is less confidence in the signal emerging in the forecast for rainfall than for temperature. The probability that UK precipitation for June-July-August will fall into the driest of our five categories is around 15% and the probability that it will fall into the wettest category is around 20% (the 1981-2010 probability for each of these categories is 20%).Click here for more detailed information on the Met Office long-term forecast.

River flows

May river flows were in the normal range across most of England and Wales and were above normal in Scotland (notably so in the north).(click here For further information on the situation at the end of May). There is a wide spread in outcomes of the ensemble-based river flow modelling, with little difference from what may be expected from climatology: the one-month-ahead outlook is strongly indicative of June river flows being in the normal range across most of Great Britain, but below normal if the month is significantly drier than average and above-normal (in northern and western localities especially) if the month is very wet. A comparison with historical analogues, coupled with the 3-month groundwater outlook, implies that river flows are likely to be higher than normal through the summer in some permeable catchments in parts of the Chalk of central southern England. For full information on the river flows outlook, click here.

Groundwater

May levels were above average across most aquifers, and notably so in parts of the Chalk (click here for further information on the situation at the end of May). The model-based outlook suggests that average groundwater levels for June are very likely to be higher than normal across most aquifers (with the exception of the Jurassic limestone and the Chalk of the Yorkshire Wolds). This situation is likely to continue for the rest of the summer: across all aquifers, levels are likely to be above normal over the next three months, with exceptional levels possible if higher amounts of rainfall are received.  Whilst above-normal levels are anticipated, note that this is relative to what is expected for the time of year; groundwater levels will still be low relative to winter conditions, and it is unlikely that these seasonally-elevated levels will be associated with flood risk. The probability of high levels spells a favourable water resources outlook for the summer, and suggests that the autumn/winter recharge season will be starting from levels that are well above the early autumn average.