May 2016


Period: From May 2016      Issued on 10.05.2016 using data to the end of April 2016

Summary

With river flows having mostly returned to normal following a very wet start to the year, the outlook for May is for normal flows in eastern parts of the UK, with normal to below normal flows over northern and western UK. This pattern is likely to persist over the next three months. Groundwater levels are likely to be within the normal range for the next three months, with the exception of the northern Permo-Triassic sandstone aquifer, which will remain notably high throughout May. Rainfall projections show a slight increase in the probability of above-average rainfall for May, though May has begun with very dry weather in eastern parts of the UK. For May-June-July there are equal chances of above- and below-average rainfall.

Rainfall

Rainfall for April was above average for the UK as a whole at approximately 120% of the 1971-2000 average. The wettest region was eastern Scotland, whilst localised areas of below average rainfall fell on southern Wales, and south-western and south-eastern England.

Predictions (released by the Met Office on 21st April 2016) for the UK show a slight increase in the probability of above-average rainfall for May. For May-June-July as a whole, the forecast for UK precipitation suggests that the chances of above- and below-average rainfall are fairly balanced. The probability that UK precipitation for May-June-July will fall into the driest of five equal categories is between 20 and 25% 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 April were predominantly normal across the UK, with some catchments displaying above normal or notably high flows.

Simulations of river flows for May suggest normal to below normal flows in the north and west of the UK and normal to above normal flows in eastern parts of the UK. However, following a particularly dry start to May in eastern parts, and with a 10-day forecast for further fair weather with only scattered light showers, normal flows will be most likely in this area during May. For the next three months the outlook is similar with river flows expected to be within the normal range in eastern parts of the UK, and normal to below normal flows being likely in northern and western UK.

Groundwater

Groundwater levels for April were normal, with above normal levels in many parts of the southern Chalk aquifer. The northern Permo-Triassic sandstone showed a continuation of the notably and exceptionally high levels that have prevailed since the beginning of the year.

Groundwater levels throughout summer in the UK are dominated by natural recessions and are relatively unaffected by rainfall. Therefore, the outlook for May is for the groundwater levels of the slowly responding northern Permo-Triassic sandstone to remain notably high. Groundwater levels elsewhere are likely to be within the normal range for the next three months.

Further information - May 2016

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