November 2013


Period: From November 2013      Issued on 13.11.2013 using data to the end of October

Summary

October was a wet month (very wet in parts of the UK) that has brought about a significant change in the hydrological situation. Soils were very dry in early October, but have become much wetter as a result of recent rainfall, leading to increases in river flows and allowing groundwater recharge to commence. As a result of this, and given a rainfall forecast that slightly favours wetter conditions, the November Outlook is suggestive of river flows being in the normal range or above, with above-normal flows more likely in western catchments. Groundwater levels are likely to be normal in most aquifers, with above-normal levels likely to persist in parts of northern England. The outlook for the next three months is for broadly similar patterns, with river flows and groundwater levels in the normal range or above. The water resources situation for the rest of autumn and early winter therefore appears favourable. 

Rainfall

Indications are that precipitation in November is more likely to be above average than below average. For November-December-January as a whole the signal for precipitation is similar to climatology, with only a slightly higher probability of above-average than below-average rainfall. The probability that UK precipitation for November-December-January will fall into the driest of our five categories is close to 15% and the probability that it will fall into the wettest category is approximately 25% (the 1981-2010 probability for each of these categories is 20%).

River flows

River flows in October were in the normal range across much of the UK, with above-average flows in a band from stretching from southwest England and south Wales through central England to Lincolnshire, areas which received substantial rainfall in late October. In contrast, below-normal flows persisted in the far north of Scotland. The one-month outlook is for November river flows to be in the normal range or above normal, with a greater likelihood of above-normal flows in central England and upland areas in the west and north. In these areas catchments are already wet and likely to respond rapidly to further rainfall.  However, below-normal flows could persist in northeast Scotland.  The three-month outlook is suggestive of normal river flows across much of the UK, but with a higher likelihood of above-normal than below-normal flows in the western uplands and in central England.

Groundwater

October groundwater levels were in the normal range across most of the Chalk aquifer (but below normal in parts of the South Downs and Yorkshire Wolds) and the Jurassic limestone of central England. Elsewhere and in other aquifers, levels were generally above normal, notably so in the Permo-Triassic sandstone and Magnesian limestone of northern England. The one-month outlook is suggestive of a continuation of the present situation, with normal levels across the Chalk contrasting with higher levels in the northwest. The same broad pattern is apparent in the three-month outlook, although above-normal levels are more likely over this timeframe in some Chalk boreholes, as recent rainfall begins to recharge the aquifer. The outlook based on historical climate ensembles suggests elevated levels in the Permo-Triassic sandstones in northern England are likely to persist for at least the next six months and possibly longer.