Wednesday, 23 September 2015

August 2015 overview

Groundwater levels, August 2015
August was wetter than average for the UK (133% of the long-term average rainfall), bring a rather damp summer to a close (126% of average rainfall for the UK for June-August).  The south coast of England had particularly high rainfall in August, with over twice average rainfall falling over large areas, and nearly three times in some places.

The focus of the wet weather in August across southern England significantly reduced soil moisture deficits in this area, and caused temporary interruptions in seasonal recessions for some boreholes. 

The majority of the index boreholes were within or close to the normal range. In the Chalk, levels generally were near or below average, although Killyglen was above normal and Westdean No.3 was exceptionally high. Seasonal recessions were temporarily halted in localised areas of southern England (Ashton Farm, West Woodyates Manor, Tilshead and Houndean Bottom) by the late August rainfall, although the recessions may have since continued. 

Levels in the Jurassic limestones fell during August and were also normal or just below; recessions were again briefly halted.  In the Magnesian limestone, although levels generally were in the normal range, they fell at Swan House and rose slightly at Brick House Farm. In the slowly responding Permo-Triassic sandstones, with the exception of Llanfair DC, levels were near or above average, with record high August levels recorded at Newbridge (for the third month in succession) and also notably high levels at Nuttalls Farm (although lower than the exceptionally high levels in July). In the fast responding Carboniferous Limestone, levels fell but remained in the normal range in the Peak District, and rose in south Wales to be above normal, reflecting differences in regional rainfall.

For more information, see the Hydrological Summary for August 2015.

Hydrological Outlook from September 2015

The latest Hydrological Outlook is available.
Hydrological Outlook from September 2015

The forecast for precipitation over September-October-November as a whole is indistinguishable from climatology.

Groundwater levels in August exhibited a very similar pattern to recent months: below normal levels in parts of the southern and eastern Chalk contrasted with normal levels elsewhere in the aquifer. 

Levels in other aquifers were mostly normal, with above normal levels in some western aquifers, and variability in the Permo-Triassic boreholes where exceptionally high levels persist in Scotland. 

The one month outlook indicates a broadly similar pattern but suggests that levels in the southwestern chalk will return to normal. The three month outlook suggests this may be a shortlived effect, and a more mixed picture of normal to below-normal levels emerges across the southern Chalk. However, below normal levels in the north-east Chalk are likely to persist. Levels in other aquifers are likely to be normal or below-normal, with above-normal levels in parts of the Permo-Triassic sandstone.

For further information see the full Hydrological Outlook for September.

Tuesday, 18 August 2015

July 2015 overview

Groundwater levels, July 2015
July was wet: the majority of UK regions registered in excess of 150% of the long-term average rainfall. Parts of north-east and south-west England, and particularly much of Scotland and East Anglia, recorded more than 200% of average rainfall, whilst near or below average rainfall was restricted to areas of Kent and Sussex, the Midlands and the far north of Scotland. 

Soil moisture deficits decreased throughout the UK in July, but despite this, levels continued to fall at all index sites except Killyglen, Pant y Lladron and Dial Farm. However, in some places recession rates slowed due to heavy rainfall in the last week of the month. 

With the exception of the fast responding Chalk at Killyglen, levels in the Chalk were near average or below, with notably low levels which persisted since the end of June at Tilshead and Dalton Holme. Levels decreased in July at Chilgrove House and Compton House and were notably low by month-end. 

Groundwater levels at Ampney Crucis in the Jurassic limestones
In the Jurassic limestones, levels fell and remained in the normal range or below, and in the Magnesian Limestone, levels remained in the normal range at Brick House Farm. 

In the Permo-Triassic sandstones, levels were near to above average, except for Llanfair DC where levels were below normal. For the second consecutive month, Newbridge recorded a new monthly maximum level. Levels at Nuttalls Farm were also exceptionally high and registered as the third highest end of July level in record from 1974. Levels in the fast responding Carboniferous Limestone of south Wales were near to above normal.

For more information, see the Hydrological Summary for July 2015.

Wednesday, 12 August 2015

Hydrological Outlook from August 2015

Hydrological Outlook from August 2015
The latest Hydrological Outlook is available.

The latest predictions for UK precipitation favour below-average rainfall for August and August-September-October as a whole.

In southern and eastern England, July groundwater levels were normal to below normal, notably so in parts of the Chalk in Hampshire, Wiltshire and Yorkshire. 

Conversely, levels were exceptionally high in parts of the slowly responding Permo-Triassic sandstones of the Midlands and southern Scotland. 

The outlook for August is for the continuation of a similar pattern. Below normal levels are likely in Wessex, Wales and eastern England, whilst above normal levels are likely to persist in parts of the Permo-Triassic aquifers. 

The outlook for the next three months is also similar, with exceptionally low levels possible in parts of the southern Chalk.

For further information see the full Hydrological Outlook for August.

Wednesday, 15 July 2015

June 2015 overview

Groundwater levels, June 2015
Overall, June was dry, especially in parts of south-east England, and sunnier than average. With dry conditions over the main outcrop areas, particularly in the far south-east, and some notably warm spells later in the month, by the end of the month soil moisture deficits (SMDs) climbed to well above the average for late June. Correspondingly, groundwater levels in all indicator wells fell during June as would be expected at this time of year, when any rainfall is likely to be lost as evapotranspiration.

In the Chalk the pattern established in recent months continued. Levels were above normal for the time of year at Little Bucket Farm (Kent), but generally levels were normal or below, with below normal levels in western parts of the aquifer (Wessex and western parts of the South Downs) and parts of East Anglia and Yorkshire. Ashton Farm in Wessex recorded its fifth lowest June average level in a 42 year record. 

In the Magnesian and Jurassic limestone aquifers levels were either normal or below, and levels in the Carboniferous Limestone of South Wales and Derbyshire remained in the normal range.  

Groundwater levels at Newbridge in the Permo-Triassic Sandstones
In the Permo-Triassic sandstones, levels were average or well above; Nuttalls Farm in the West Midlands saw exceptionally high levels while Newbridge (south west Scotland) reached a record high for June (see hydrograph).  These aquifers respond slowly to changes in rainfall, and the latter is located in an area that has seen moderately above-average rainfall over recent months.

For more information, see the Hydrological Summary for June 2015 [PDF].

Tuesday, 14 July 2015

Hydrological Outlook from July 2015

The latest Hydrological Outlook is available.
Hydrological Outlook for July 2015

The latest predictions for UK precipitation favour near- or below-average rainfall during July and for July-August-September as a whole.

Groundwater levels in June exhibited a very similar pattern to recent months: below normal levels in parts of the southern and eastern Chalk contrasted with normal levels elsewhere in the aquifer.  Levels in other aquifers were mostly normal or below, except in some Permo-Triassic boreholes where exceptionally high levels persist. 

This pattern is likely to continue through July, with recessions largely unaffected by summer rainfall. Over the three month timeframe (Jul-Sep), model projections suggest that groundwater levels in some areas with below normal levels may be trending towards the normal range. However, analysis of historical analogues suggests that this may be unrealistic and that below normal levels in Wessex and the Yorkshire Chalk are likely to persist into early autumn. The onset of the recharge season is likely to be delayed in areas in which below normal levels persist in the longer term.

For further information see the full Hydrological Outlook for July.

Wednesday, 24 June 2015

May 2015 overview

Recessions in groundwater levels continued during May, despite the wet conditions over much of the UK. Soil moisture deficits (SMDs) have become established in south-eastern areas, meaning rainfall is taken up by the soil rather than recharging aquifers. 
Groundwater levels, May 2015

Across most Chalk aquifers, levels remained normal although they declined at a slightly faster rate than is typical. In Yorkshire, Wetwang and Dalton Holme were notably low. Compared to April, more of the Wessex and Hampshire Chalk was below normal; notably low levels were recorded at Ashton Farm and Tilshead, which recorded its sixth lowest May level in 47 years. Only two Chalk boreholes (Therfield Rectory and Little Bucket Farm) recorded above normal levels – these boreholes continued to be influenced by the wet conditions of 2013/14. 

Elsewhere the situation was mixed. In south-west England and south Wales, levels remained normal. Levels in the Jurassic limestone were below normal in southern areas and nearer normal further north. Swan House, in the Magnesian Limestone, was an exception, recording below normal levels due to limited recharge this winter. 

Several Permo-Triassic boreholes remained at exceptionally high levels, the legacy of exceptional recharge in 2013/14, whilst others were close to their seasonal norms. An exception was Llanfair D.C. in north Wales, where levels were slightly below normal. 

Any moderation of recessions in the Chalk from a wet May was yet to show at month-end. Low levels in Wessex and Hampshire may persist through the summer or decline further, though still well above the minima of 2011/12.

For more information, see the Hydrological Summary for May 2015 [PDF].