During both winters 2015/16 and 2016/17, the weather over the UK and much of continental Europe reflected the North Atlantic Jetstream being stuck in more or less the same position for weeks or months on end. Winter 2015/16 was marked by a succession of low pressure systems passing over / close to the British Isles, bringing strong winds and truly exceptional rainfall particularly during the late autumn and early winter. Autumn 2016 and the early winter 2016/17, by contrast, was calm, often bright and generally very dry, especially December. This reflected a persistently very anticyclonic (high pressure) pattern. Notes on both winters below:
Flood Reports
1. Barker, Lucy; Hannaford, Jamie; Muchan, Katie; Turner, Stephen; Parry, Simon. 2016 The winter 2015/2016 floods in the UK: a hydrological appraisal [in special issue: The exceptional winter of 2015/16 in the UK and Ireland] Weather, 71 (12). 324-333. 10.1002/wea.2822
2.
Autumn 2016 and the early winter 2016/17, by contrast, were calm, often bright and generally very dry. Up to the first week of January 2017, there were only three named storms five as of the end of February. This reflected a persistently very anticyclonic (high pressure) pattern. For much of the winter, the low pressure systems passed well to the north of the British Isles, over Iceland, in line with a meandering jetstream looping up into the Arctic and down again through Russia and eastern Europe. To the south and west of it, an extensive tongue of high pressure encompassed the British Isles and much of continental Europe, stretching from Scotland to the Mediterranean. This is what meteorologists call an omega block. In December some of these anticyclones were intense, with central pressures upwards of 1040 millibars. Of the three low pressures which touched the British Isles, two of them, Storms Barbara and Conor around Christmas 2016, passed to the north. Only one, Storm Angus in November, brought notable rainfall, albeit with flooding and flood warnings, to southern Britain and France as it tracked to the south, along the English Channel. The good news: other than Storm Angus, the winter was been largely flood-free, following a bright autumn with strong leaf colour persisting well into November. During December 2016 and early January 2017 there has been a good deal of dry and bright weather, making for crisp, cold frosty days, fine sunsets over our local coast and plenty of winter sunshine. Walks have been much more pleasant without the mud and waterlogged paths we usually have to contend with during the winter. The downer: falling river and groundwater levels.
Because evaporation rates are low in the cooler weather and it is the off season for plant growth, winter rainfall is vital to recharge soils, rivers, aquifers, and public water supply; especially in densely populated areas such as southeast England. This is something we could well pay for once evaporation resumes come the warmer spring and summer, especially if spring is early, warm and dry. Droughts followed dry winters in 1975/76, the succession in the early 1990s, 2005/06 and 2010/11. By late December, I'd already noticed the levels in some of the Wessex chalkstreams, including the Nadder and the Avon around Salisbury, falling. In their monthly hydrological summary for November and December, the Centre for Ecology and Hydrology (CEH) said that some areas of the UK needed to be "vigilant" in the event of a dry winter, due to low reservoir stocks, especially in SE England where one reservoir was under half full (Ardingly, East Sussex). By the end of December, both CEH (UK) and the Environment Agency (England) said that most rivers across the UK were running below their respective long term gauged averages, some of them exceptionally so (red symbols on River Flow maps): among them the Exe, Wye, Welsh Dee, the Dorset Stour; and the rivers of East Sussex and Kent. One (the Eastern Rother at Udiam) was down to just 6% of its long term average mean monthly flow for December. Even the chalk streams in Wessex, usually relatively slow to rise and fall, were feeling it: with the Salisbury Avon under 40% LTA and the Itchen 72%. The groundwater in many index wells in the southern Chalk had not recharged and was still falling in some cases, eg Chilgrove.
2015 / 16
In the Met. Office's first year of asking the public to name storms (low pressure systems bringing strong winds), eleven named storms affected the British Isles between early November and late March. There was major, widespread flooding in northern and western Britain, with some exceptional outflows and river flows.
For my notes on the flood events of winter 2015/16, please see:
Rain and Flood Fury in the North , published 10th December 2015, written after the first round of major flooding in northern Britain, most notably Cumbria for the third time in little over ten years.
Difficult Confluences in the North, published 27th December 2015, written just after the Christmas 2015 floods, hitting the north yet again, most notably this time Yorkshire.
Flood Reports
1. Barker, Lucy; Hannaford, Jamie; Muchan, Katie; Turner, Stephen; Parry, Simon. 2016 The winter 2015/2016 floods in the UK: a hydrological appraisal [in special issue: The exceptional winter of 2015/16 in the UK and Ireland] Weather, 71 (12). 324-333. 10.1002/wea.2822
2.
- UK Winter 2015/2016 floods report published | National River Flow Archive
Marsh,
T.J.1, Kirby, C.2, Muchan, K.1, Barker, L.1, Henderson, E.2 and Hannaford,
J.1 2016. The winter floods of 2015/2016 in the UK - a
review. Centre for Ecology &
Hydrology, Wallingford, UK.
37 pages.
Affiliations: 1Centre for Ecology & Hydrology; 2British
Hydrological Society.
ISBN: 978-1-906698-61-4
Both reports give a comprehensive appraisal of the UK hydrology (river flows, run-off, groundwater, soil moisture) and the weather (rainfall) influencing it. Data from the Met. Office, Environment Agency, SEPA, Natural Resources Wales and the UK, the Centre for Ecology and Hydrology, National Hydrological Monitoring Programme, UK National River Flow Archive. Both reports are publicly available online.
Key points:
The rainfall in northern and western Britain in November and December was truly exceptional. December 2015 was the wettest of any calendar month in the UK, in the Met.Offices's series going back to 1910. It was the second wettest winter (December - February). A new daily (24) hour rainfall record at Honister Pass, Cumbria 5/6th December, 341mm, breaking the previous record of 314mm at Nearby Seathwaite in November 2009.
This came after a sharp turn around in rainfall and river flows in November 2015. The early autumn (September and October) was relatively dry, with many rivers running below average for the time of year. Heavy rainfall through November rapidly saturated soils, meaning run off into rivers was subsequently rapid, especially in northern and western impermeable catchments.
Some impressive, record breaking river flows were recorded at gauging stations in northern and western Britain. However, records generally go back to the 1950s and 1960s, therefore representing a relatively short timescale. Flows are likely to have been higher during the historical past.
New peak flow records / notable flows:
During the Storm Desmond floods, 5-6th December, the Eden, Tyne and Lune all peaked at around 1700 cubic metres per second, the highest of all being the Lune at Caton, all the more remarkable considering it has a smaller catchment than the other two. These are the highest flows recorded on any river in England, and among the highest in Britain. They reckon the flow on the Tyne was the highest since the great flood of 1771, though that was estimated to be nearly 4000 cubic metres per second.
As well as the above, the Tay, Tweed, Dee in NE Scotland and the Ribble all attained peak flows of at least 1000 cubic metres per second. The Tay, at Ballathie in central Scotland has the highest flows of any British river, it's highest recorded peak flow was in excess of 2000 cubic metres per second in the January 1993 floods. Though it didn't get that high this time, the peak flow in early January 2016 was around 1800 cubic metres per second; and daily flows were 1000+ cubic metres per second on eight days December 2015 - January 2016.
Total outflow (run-off) from all rivers and lakes in Britain is useful for comparing flood events. A 24 hour new record was set 5th/6th December 2015, exceeding the previous one in December 2006 by a large margin. 6th, 26th, 30th December 2015 all in the top 24 hour totals. The winter also ranks high when run-off is measured over longer periods, of up to 90 days.
During the drier weather of the spring and early summer, water levels on some of the above notorious rivers fell steeply: the Eden (Sheepmount, Carlisle) registered new seasonal flow minima in May and June, on 19 days, and a consecutive 12 days.
Anthropogenic climate change is a likely aggravating factor, potentially changing rainfall patterns, melting Arctic ice possibly slowing down the jetstream, making blocked weather patterns more likely. As well as being exceptionally wet, December 2015 was also exceptionally mild, with daffodils flowering in southern England before Christmas, highs of up to 17C in southern England / the Midlands, more like April. However, this is superimposed on the high natural variability of Britain's weather. This variability was demonstrated during the contrasting winter which followed.
The rainfall in northern and western Britain in November and December was truly exceptional. December 2015 was the wettest of any calendar month in the UK, in the Met.Offices's series going back to 1910. It was the second wettest winter (December - February). A new daily (24) hour rainfall record at Honister Pass, Cumbria 5/6th December, 341mm, breaking the previous record of 314mm at Nearby Seathwaite in November 2009.
This came after a sharp turn around in rainfall and river flows in November 2015. The early autumn (September and October) was relatively dry, with many rivers running below average for the time of year. Heavy rainfall through November rapidly saturated soils, meaning run off into rivers was subsequently rapid, especially in northern and western impermeable catchments.
Some impressive, record breaking river flows were recorded at gauging stations in northern and western Britain. However, records generally go back to the 1950s and 1960s, therefore representing a relatively short timescale. Flows are likely to have been higher during the historical past.
New peak flow records / notable flows:
During the Storm Desmond floods, 5-6th December, the Eden, Tyne and Lune all peaked at around 1700 cubic metres per second, the highest of all being the Lune at Caton, all the more remarkable considering it has a smaller catchment than the other two. These are the highest flows recorded on any river in England, and among the highest in Britain. They reckon the flow on the Tyne was the highest since the great flood of 1771, though that was estimated to be nearly 4000 cubic metres per second.
As well as the above, the Tay, Tweed, Dee in NE Scotland and the Ribble all attained peak flows of at least 1000 cubic metres per second. The Tay, at Ballathie in central Scotland has the highest flows of any British river, it's highest recorded peak flow was in excess of 2000 cubic metres per second in the January 1993 floods. Though it didn't get that high this time, the peak flow in early January 2016 was around 1800 cubic metres per second; and daily flows were 1000+ cubic metres per second on eight days December 2015 - January 2016.
Total outflow (run-off) from all rivers and lakes in Britain is useful for comparing flood events. A 24 hour new record was set 5th/6th December 2015, exceeding the previous one in December 2006 by a large margin. 6th, 26th, 30th December 2015 all in the top 24 hour totals. The winter also ranks high when run-off is measured over longer periods, of up to 90 days.
 |
| The Eden (right) and Caldew (left) at Carlisle in the calm of the early autumn (September 2016) |
Anthropogenic climate change is a likely aggravating factor, potentially changing rainfall patterns, melting Arctic ice possibly slowing down the jetstream, making blocked weather patterns more likely. As well as being exceptionally wet, December 2015 was also exceptionally mild, with daffodils flowering in southern England before Christmas, highs of up to 17C in southern England / the Midlands, more like April. However, this is superimposed on the high natural variability of Britain's weather. This variability was demonstrated during the contrasting winter which followed.
2016/17
 |
| Calm weather beneath and anticyclone, Chichester Harbour 27/12/16 |
 |
| The dry River Lavant, East Lavant 21/01/17 |
Because evaporation rates are low in the cooler weather and it is the off season for plant growth, winter rainfall is vital to recharge soils, rivers, aquifers, and public water supply; especially in densely populated areas such as southeast England. This is something we could well pay for once evaporation resumes come the warmer spring and summer, especially if spring is early, warm and dry. Droughts followed dry winters in 1975/76, the succession in the early 1990s, 2005/06 and 2010/11. By late December, I'd already noticed the levels in some of the Wessex chalkstreams, including the Nadder and the Avon around Salisbury, falling. In their monthly hydrological summary for November and December, the Centre for Ecology and Hydrology (CEH) said that some areas of the UK needed to be "vigilant" in the event of a dry winter, due to low reservoir stocks, especially in SE England where one reservoir was under half full (Ardingly, East Sussex). By the end of December, both CEH (UK) and the Environment Agency (England) said that most rivers across the UK were running below their respective long term gauged averages, some of them exceptionally so (red symbols on River Flow maps): among them the Exe, Wye, Welsh Dee, the Dorset Stour; and the rivers of East Sussex and Kent. One (the Eastern Rother at Udiam) was down to just 6% of its long term average mean monthly flow for December. Even the chalk streams in Wessex, usually relatively slow to rise and fall, were feeling it: with the Salisbury Avon under 40% LTA and the Itchen 72%. The groundwater in many index wells in the southern Chalk had not recharged and was still falling in some cases, eg Chilgrove.
Apart from a brief period following the passage of Storm Angus, water levels across the Channel in much of France have been well down since the late summer Eaufrance, http://www.eaufrance.fr/ . There, the anticyclonic autumn and early winter came after a hot dry late summer, with heatwaves in some areas, such as Paris. It was much the same here in autumn-early winter 2015/16; but then a shift in weather patterns in January 2016 enabled recharging rainfall. Notably low levels in Loire and tributary valleys western France / Brittany.
In the second week of January 2017, the synoptic pattern shifted temporarily, though not before it plunged bitterly cold Arctic air well down into southeastern Europe, with snow in Greece and Turkey. Bitter cold in normally relatively warm areas not used to it. In comparison, the wintry weather affecting the UK later that second week was trivial. Even so, it brought not only the customary transport disruption but also tidal surges along the North Sea coast of Britain. Early on the morning of Friday the 13th, the Environment Agency had 17 Severe Flood Warnings (potential danger to life) along the Essex and East Anglia coasts, plus a rising number - 90+ by midday - of Flood Warnings and 80+ flood alerts during the middle of the morning.
http://www.bbc.co.uk/news/uk-38605842
http://www.bbc.co.uk/news/uk-38594739
In the second week of January 2017, the synoptic pattern shifted temporarily, though not before it plunged bitterly cold Arctic air well down into southeastern Europe, with snow in Greece and Turkey. Bitter cold in normally relatively warm areas not used to it. In comparison, the wintry weather affecting the UK later that second week was trivial. Even so, it brought not only the customary transport disruption but also tidal surges along the North Sea coast of Britain. Early on the morning of Friday the 13th, the Environment Agency had 17 Severe Flood Warnings (potential danger to life) along the Essex and East Anglia coasts, plus a rising number - 90+ by midday - of Flood Warnings and 80+ flood alerts during the middle of the morning.
http://www.bbc.co.uk/news/uk-38605842
http://www.bbc.co.uk/news/uk-38594739
Snow / tidal surges - Europe
http://www.bbc.co.uk/news/world-europe-38607862
In the third week of January, the omega block pattern, with high pressure over Britain and continental Europe became established once again, the pressure at home in south Hampshire rising to 1039 millibars on Wednesday 18th January. It then fell slowly, before sticking around 1028 millibars. Once again, a good deal of bright, crisp frosty weather. When we went out walking at the weekend, it was a pleasant change not to have to wade through lots of mud, much of being frozen, at least during the morning. As I'd expected, however, there was no water in the River Lavant when I walked along Sheepwash Lane, East Lavant and up to the Trundle. The first no-show of the winterbourne for five years.
The final full week of January began with widespread freezing fog, icy pavements being a particular problem in the immediate area where I live. There, it is usually the motorway noise I tend to hear when the air is still. This time (overnight 23rd / 24th January), it was distant foghorns. In the very still air, air pollution levels rose as there was little or no wind to disperse the fumes (NOx, particulates) from traffic and wood burning. What wind there was (easterly - southeasterly) brought more pollution from the continent. Though pollution levels on the Hampshire coast were lower than they were in London, some stretches of road felt smelt very fumy. I got to the mouth of the River Hamble on the Warsash shore on Tuesday 24th January late morning. By then the sun was coming through and the mist was clearing, though Fawley refinery was still largely shrouded; the top third of the power station chimney poked out of the mist. To the south, a hazy silhouette of Calshot Castle, but the IOW was completely shrouded; still the occasional sounds of foghorns out in the Solent. What was really noticeable, though was the low note industrial hum in the air. Presumably from the refinery across the water; perhaps noise from the container port at Southampton, too. Normally, we don't tend to hear these. Aircraft noise more noticeable than usual, too.
February and March were more mixed, allowing for a pick up in river flows at least temporarily; and to some extent groundwater reserves. Yet, the rainfall was episodic, with dry anticyclonic spells in between. It was also very mild, meaning that spring didn't wait.
In February, most of the rain fell during the first and last weeks of the month. During the final week (23rd), the fourth named storm, Doris. This affected mostly the Midlands and north, with high winds and snow on hills. Euan followed a few days later (26th). Most of the action its action was over Ireland, the Irish weather service having named the storm. During the middle of the month, though, high pressure re-established as a very intense high (central pressure over northern Scandinavia 1051 millibars at one point) drifted south over continental Europe. Though western and northern parts of Britain received above average rainfall during March, rainfall was below average in SE England (Met. Office 1981-2010 average, with records from 1910).
Links
Water and weather information:
UK Meteorological Office
http://www.metoffice.gov.uk/public/weather
Environment Agency (flood warnings, England)
https://flood-warning-information.service.gov.uk/
Environment Agency (rivers and sea levels, England)
https://flood-warning-information.service.gov.uk/river-and-sea-levels
Environment Agency - monthly and weekly water resources reports (England)
https://www.gov.uk/government/collections/water-situation-reports-for-england
SEPA (Scottish Environmental Protection Agency)
http://apps.sepa.org.uk/waterlevels/
Natural Resources Wales
http://naturalresources.wales/our-evidence-and-reports/maps/river-levels-online/?lang=en
Centre for Ecology and Hydrology -monthly hydrological summaries for the UK, UK National River Flow Archive and National Hydrological Monitoring Programme:
Monthly hydrological summaries:
http://nrfa.ceh.ac.uk/monthly-hydrological-summary-uk
Gauged river flow data - http://nrfa.ceh.ac.uk/data/search
UK Meteorological Office
http://www.metoffice.gov.uk/public/weather
Environment Agency (flood warnings, England)
https://flood-warning-information.service.gov.uk/
Environment Agency (rivers and sea levels, England)
https://flood-warning-information.service.gov.uk/river-and-sea-levels
Environment Agency - monthly and weekly water resources reports (England)
https://www.gov.uk/government/collections/water-situation-reports-for-england
SEPA (Scottish Environmental Protection Agency)
http://apps.sepa.org.uk/waterlevels/
Natural Resources Wales
http://naturalresources.wales/our-evidence-and-reports/maps/river-levels-online/?lang=en
Centre for Ecology and Hydrology -monthly hydrological summaries for the UK, UK National River Flow Archive and National Hydrological Monitoring Programme:
Monthly hydrological summaries:
http://nrfa.ceh.ac.uk/monthly-hydrological-summary-uk
Gauged river flow data - http://nrfa.ceh.ac.uk/data/search
Eaufrance - http://www.eaufrance.fr/ (monthlyhydrological summaries)
Vigicrues (flood warnings and gauged river flows)
http://www.vigicrues.gouv.fr/
Meteofrance (the French weather service) say that December 2016 was marked by record sunshine and exceptionally low rainfall, the rainfall deficit surpassing that of December 2015.
http://www.meteofrance.fr/actualites/44311414-decembre-2016-tres-sec-et-ensoleille
Media Reports:
BBC News - http://www.bbc.co.uk/news
The Guardian - https://www.theguardian.com/uk
Potential influence of melting Arctic ice on weather patterns (The Guardian 19th December)
https://www.theguardian.com/environment/2016/dec/19/arctic-ice-melt-already-affecting-weather-patterns-where-you-live-right-now?
Cold weather in Europe (January 2017)
Media Reports:
BBC News - http://www.bbc.co.uk/news
The Guardian - https://www.theguardian.com/uk
Potential influence of melting Arctic ice on weather patterns (The Guardian 19th December)
https://www.theguardian.com/environment/2016/dec/19/arctic-ice-melt-already-affecting-weather-patterns-where-you-live-right-now?
Cold weather in Europe (January 2017)
European
cold wave circa 8th January
UK
Wintery weather/ tidal surge 12/01/17
Freezing fog / air pollution:
BBC News
23rd January (London smog alert)
Guardian
23rd - 24th January
