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].

Tuesday, 16 June 2015

Hydrological Outlook from June 2015

The latest Hydrological Outlook is available.

In the Chalk, May groundwater levels were mainly normal in the south-east, but levels were below normal (and notably low in some boreholes) in parts of southern England and Yorkshire. 

Levels were mixed in other aquifers, with exceptionally high levels persisting in parts of the Permo-Triassic sandstone. 

The one month outlook suggests a similar situation will continue in June, although levels in the Permo-Triassic are likely to be notably high rather than exceptional. 

The groundwater situation is unlikely to change significantly through the summer; the three month outlook suggests normal levels will dominate, but with below-normal levels persisting in parts of north-east and southern England (although there is a possibility that levels in some parts of Wessex may return to normal).

For further information see the full Hydrological Outlook for June.

Wednesday, 20 May 2015

April 2015 overview

Groundwater levels, April 2015
With little rainfall and some very warm weather, soil moisture deficits (SMDs) climbed steeply through April and, by month end, were substantially above average across the main aquifer areas (SMDs were double the typical end-of-April magnitude across the Chalk outcrop).

Consequently, levels fell at index wells throughout the country, with a few exceptions: the slowly-responding Chalk at Therfield Rectory and Dial Farm in eastern England, the Permo-Triassic sandstones at Nuttalls Farm and the Carboniferous Limestone at Alstonfield in the Midlands.

In the Chalk, levels were generally still within the normal range but below average for the time of year in Yorkshire, Northern Ireland and Dorset-Wiltshire, whilst they remained above average in the eastern part of the North Downs and upper Lee valley of Hertfordshire. However, compared with the exceptionally high groundwater levels in the Chalk in April 2014, when groundwater flooding was still present in some areas, they are now up to 4 m lower across southern England (and over 6 m and 12 m lower at Therfield Rectory and Stonor Park, respectively).
Groundwater level hydrograph, Stonor Park (unconfined  Berkshire Downs Chalk)
In the fast responding Jurassic and Magnesian limestones, levels remained average or below and in the slow responding Permo-Triassic sandstones they were average or above (still exceptionally high at Newbridge, an area receiving above‑average autumn and winter rainfall, and Nuttalls Farm). Groundwater levels in the Lower Greensand of south-east England remained above average. With the modest rise in level at Alstonfield, Carboniferous Limestone levels were in the normal range in both Derbyshire and south Wales.

As little recharge is anticipated from now until the autumn, the current picture is likely to persist unless substantial late spring or summer rainfall is received.

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