April 2014


Period: From April 2014      Issued on 09.04.2014 using data to the end of March

Summary

March was dry across much of the UK, with the settled weather continuing into the first week of April. Generally, the dry spell led to a fall in river flows and groundwater levels from the exceptional high flows and levels witnessed in the winter. River flows are now predominantly in the normal range. Higher than normal groundwater levels persist in southern England, where there is a substantial amount of water from winter rainfall stored in the Chalk aquifer and this continues to maintain river flows in groundwater-fed catchments. The outlook suggests that this picture will persist into April and beyond. Generally, conditions normal for the time of year are most likely over the coming three months. However, above normal levels and flows may persist into early summer in parts of southern England. The water resources outlook for the summer is very favourable. 

Rainfall

Latest predictions for UK precipitation are largely indistinguishable from climatology for both April and April-May-June as a whole. The probability that UK precipitation for April-May-June will fall into the driest of five equal classes is between 10 and 15% and the probability that it will fall into the wettest of five equal classes is between 20 and 25% (the 1981-2010 probability for each of these categories is 20%). 

River flows

March river flows were in the normal range across much of England and Wales but above normal in the south-east, exceptionally so in some groundwater-fed catchments. In Scotland, river flow patterns were mixed, with mainly normal to above normal flows except in some catchments in the far north where flows were below normal. The one-month outlook indicates April flows are likely to be in the normal range across most of Great Britain, although above-normal flows are very likely to persist in parts of southern England. There is an increased likelihood of above normal flows in parts of southern Scotland and northern England where above-average rainfall was received in March. The three month outlook is generally suggestive of normal flows across Great Britain, as river flows continue to recede. In responsive catchments in northern Britain, and particularly in north-east Scotland, there is a likelihood of below normal flows, while above normal flows are more likely to persist in some groundwater-fed catchments in southern England.

Groundwater

March groundwater levels were substantially above average across much of the Chalk (although levels were normal in parts of East Anglia and Yorkshire), the Permo-Triassic sandstones and the Magnesian limestones. Normal levels were observed in the Jurassic limestones. In the southern Chalk the one month outlook is dependent on local characteristics of the aquifer and is likely to range from normal to exceptionally high. In the Permo-Triassic sandstones, levels are likely to remain above normal in central and northern Britain, exceptionally so in north-west England and southern Scotland, but to return to normal in south-west England. Over the next three months, groundwater levels will continue to fall and with increasing evapotranspiration reducing recharge, levels are likely to return to normal in many places. Above normal levels will probably persist in parts of the southern Chalk. 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.