May 2014


Period: From May 2014      Issued on 12.05.2014 using data to the end of April

Summary

For the UK as a whole April rainfall was close to average, but with marked variability that is significant for the current outlook.  May river flows are likely to be in the normal range for much of the country, but in the parts of eastern England that have recently been dry, below-normal flows are likely, and in southern England, above-normal river flows and groundwater levels are likely as a  continuing consequence of the exceptional winter rainfall and a wet April. Groundwater levels in slowly-responding aquifers in north-west England and southern Scotland will remain exceptionally high. These regional differences are likely to persist in the longer term. The water resources outlook for the summer remains favourable.  

Rainfall

Latest predictions for UK precipitation are largely indistinguishable from climatology for both May and May­-June-July as a whole. The probability that UK precipitation for May­June­July will fall into the driest of five categories is between 20% and 25% and the probability that it will fall into the wettest of five categories is close to 25% (the 1981­2010 probability for each of these categories is 20%).

River flows

April river flows were in the normal range for much of the UK, but above normal in catchments in central southern England and in parts of central Scotland, whilst below normal in north-east Scotland and parts of eastern England. Overall, the one-month outlook suggests flows being in the normal range for much of the UK but with some regional contrasts: normal to above-normal flows are likely in southern England, and parts of north-east England and south-east Scotland; elsewhere, the outlook indicates normal to below normal flows, with lower flows most likely in northern Scotland and parts of East Anglia. The three month outlook indicates normal to below normal flows in eastern England and across northern and western Britain. In southern England, flows are most likely to be normal, but above normal flows will probably persist well into the summer in some slowly-responding groundwater-influenced catchments in parts of southern England.

Groundwater

Following the onset of the spring recession in groundwater levels, some boreholes had returned to near normal levels in April although they still remained high or exceptionally high at slowly responding sites, for example in the Permo-Triassic sandstones and a few Chalk sites in southern England. In the southern Chalk the one-month outlook for groundwater levels is generally for above normal levels, although this is dependent on local characteristics of the aquifer and ranges from normal to exceptionally high. In the Permo-Triassic sandstones, levels are likely to remain above normal, exceptionally so in north-west England and southern Scotland. Over the next three months, groundwater levels will continue to fall as  increasing evapotranspiration reduces recharge, and levels will tend towards normal in many places. Above normal levels will probably persist in parts of the southern Chalk and northern Permo-Triassic sandstones. Whilst levels may be above normal for the time of year, high groundwater levels in the late spring and early summer are unlikely to cause any new groundwater related flooding.