August 2014


Period: From August 2014      Issued on 12.08.2014 using data to the end of July

Summary

July saw some long spells of fine summer weather and the month was drier than average for the UK as a whole. However, as is often the case for this time of year, there were marked spatial and temporal variations, reflecting the showery nature of summer rainfall. As a consequence conditions at the start of August are spatially variable. The general pattern for August is for river flows to be below normal in the north and west of the UK, while above normal flows are likely to the south and east. With the locally stormy conditions persisting into early August, the situation could change rapidly, especially in responsive catchments in the north and west. For groundwater, the situation will continue broadly unchanged with some areas of higher than normal groundwater levels. The  three month outlook is for  a return to normal flows and groundwater levels. 

Rainfall

The latest predictions for UK-mean precipitation for both August and August-September-October as a whole slightly favour above-average precipitation although below-average is almost as likely.

The probability that UK precipitation for August-September-October will fall into the driest of five categories is around 20% and the probability that it will fall into the wettest category is 25-30% (the probability for each of these categories over the climatological period 981-2010 is 20%).

River flows

July saw a contrast between southern and eastern England, where flows were above-normal, and northern and western parts of the UK, where flows were generally below-normal (and notably so in some catchments). The one-month outlook is for this broad contrast to continue. Normal to below- normal flows are likely in the north and west, although catchments in these regions are typically responsive and the locally heavy rainfall experienced in early August rainfall will influence the outcome. Normal to above-normal flows are very likely to persist in southern and eastern areas. The three-month outlook suggests flows are most likely to return to the normal range across the whole of the UK. 

Groundwater

The groundwater situation in July was very similar to the previous few months. Above normal levels continued in parts of the Chalk in southern England, but normal levels now predominate across much of the aquifer. Levels in the Permo-Triassic sandstone were above normal, with record levels in some boreholes in northwest and southwest England. The one-month outlook is for similar patterns to persist, irrespective of the August rainfall, as soil moisture deficits limit the potential for recharge in summer. Over the next three months, entering the autumn, rainfall will be far more influential in dictating the outlook, so the projections are less certain. However, given typical rainfall amounts levels are likely to continue to decrease, meaning a return to normal in more boreholes in the southern Chalk and Permo-Triassic sandstone. The general outlook is for groundwater levels to be in the normal range across the majority of aquifers.