Water Situation Report
Monthly water situation report England Summary – August 2017 The August rainfall total for England was just over the monthly long term average (LTA) at 105%. Monthly rainfall totals were normal or higher for the time of year across the majority of hydrological areas. Soil moisture deficit increased during August across much of England and at the end of the month, soils were drier than average across east and central England. Monthly mean river flows increased compared to July at more than two-thirds of indicator sites and were classed as normal or higher or the time of year at all but 3 sites. Groundwater levels decreased at all but 3 indicator sites during August but end of month levels were normal or higher for the time of year at half of the indicator sites. Reservoir stocks decreased at just over half of reported reservoirs or reservoir groups, but stocks remain normal or higher for the time of year at nearly three-quarters of sites. Overall reservoir storage for England decreased slightly during August to 79% of total capacity.
Rainfall August rainfall was highest in north-west England and lowest across parts of east and north-east England, with totals ranging from 170mm in parts of Cumbria to approximately 40mm across parts of Lincolnshire, Norfolk and Northumbria. Rainfall totals were above the long term average (LTA) for August across two-thirds of hydrological areas, with parts of Kent and West Sussex receiving just over 150% of the August LTA. (Figure 1.1). August rainfall totals were classed as normal or higher for the time of year across almost all of the hydrological areas. Cumulative rainfall totals for the past 3 months range from normal to notably high for the time of year across the whole of England. In contrast, cumulative rainfall totals for the past 12 months still show a rainfall deficit with most of England being below normal or notably low for the time of year (Figure 1.2). At a regional scale, August rainfall totals ranged from 99% of the LTA in north-east England to 126% in south-east England and were normal for the time of year across all regions. The monthly rainfall total for England was 105% of the 1961-90 LTA for August (108% of the 1981-2010 LTA) (Figure 1.3).
Soil moisture deficit Despite the above average August rainfall across much of England, soil moisture deficits (SMDs) generally increased during August. At the end of August, soils were drier than at the end of July across nearly two-thirds of England, with SMDs ranging from approximately 1mm in parts of north-west England to nearly 160mm across parts of Norfolk and Cambridgeshire. Soils were drier than the August LTA across much of central and east England in particular, but wetter than average elsewhere, particularly across parts of Devon and Cornwall (Figure 2.1). At a regional scale, soils were drier at the end of August compared to the end of July across all regions, with end of month SMDs ranging from 29mm in north-west England to 99mm in east England. Soils were drier than the LTA in east and central England but wetter elsewhere (Figure 2.2).
River flows Compared with July, monthly mean river flows for August increased at just over two-thirds of indicator sites across England. River flows were classed as normal or higher for the time of year at all but 3 indicator sites; flows in the rivers Itchen and Eastern Rother were below normal for the time of year whilst the River Coln remained exceptionally low for the second consecutive month. Flows at all indicator sites in north-west England were above normal for the time of year, with the River Derwent being notably high (Figure 3.1). At the regional index sites, monthly mean river flows were normal for the time of year at 4 of the 6 sites, whilst the River Lune in north-west England and the Bedford Ouse in east England were above normal (Figure 3.2).
All data are provisional and may be subject to revision. The views expressed in this document are not necessarily those of the Environment Agency. Its officers, servants or agents accept no liability for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained herein.
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© Environment Agency 2017
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Groundwater levels Groundwater levels decreased during August at all but 3 of the indicator sites – levels at Wetwang (Hull and East Riding chalk aquifer), Crow Lady Farm (Fylde and Preston sandstone aquifer) and Woodyates (Upper Dorset Stour chalk aquifer) all increased slightly compared to the end of July. End of month groundwater levels were below normal or lower for the time of year at half of the indicator sites, with Ashley Green (Chilterns East chalk aquifer) and Little Bucket (East Kent Stour chalk aquifer) both remaining exceptionally low for the third consecutive month. End of month groundwater levels at the major aquifer index sites ranged from exceptionally low for the time of year at Little Bucket (East Kent Stour chalk aquifer) to normal for the time of year at Heathlanes (Shropshire sandstone aquifer), Dalton Holme (Hull and East Riding chalk aquifer) and Skirwith (Carlisle Basin and Eden Valley sandstone aquifer) (Figures 4.1 and 4.2).
Reservoir storage Reservoir stocks decreased at just over half of the reported reservoirs or reservoir groups during August. Notable decreases occurred at Carsington and Ogston (9%), Bough Beech (9%) and Chew Valley (12%) reservoirs, whilst Clywedog reservoir increased by 11%. End of month stocks were classed as normal or higher for the time of year at nearly three-quarters of all reported reservoirs and reservoir groups. The remaining sites were classed as below normal or notably low for the time of year (Figure 5.1). Compared with the end of July, regional reservoir stocks increased in north-west and central England by 4% and 2% respectively and decreased elsewhere by up to 3%. End of August stocks ranged from 67% of total capacity in south-west England to 87% in east England. Overall storage for England decreased slightly to 79% of total capacity (Figure 5.2).
Forward look The first half of September is likely to see a mix of clear spells and heavy showers across most of the country. The second half of September is likely to see more settled spells – especially in the south, south-east and west of the country. For the 3-month period September to November above-average rainfall is considered slightly more probable than below-average rainfall but the forecast is uncertain1. Projections for river flows at key sites2 Two-thirds of the modelled sites have a greater than expected chance of cumulative river flows being below normal or lower by both the end of September 2017 and the end of March 2018. For scenario based projections of cumulative river flows at key sites by September 2017 see Figure 6.1 For scenario based projections of cumulative river flows at key sites by March 2018 see Figure 6.2 For probabilistic ensemble projections of cumulative river flows at key sites by September 2017 see Figure 6.3 For probabilistic ensemble projections of cumulative river flows at key sites by March 2018 see Figure 6.4 Projections for groundwater levels in key aquifers2 Half of the modelled sites have a greater than expected chance of below normal or lower groundwater levels for the time of year at the end of September 2017. By March 2018, just over a third of all modelled sites have a greater than expected chance of notably low or lower groundwater levels for the time of year. For scenario based projections of groundwater levels in key aquifers in September 2017 see Figure 6.5 For scenario based projections of groundwater levels in key aquifers in March 2018 see Figure 6.6 For probabilistic ensemble projections of groundwater levels in key aquifers in September 2017 see Figure 6.7 For probabilistic ensemble projections of groundwater levels in key aquifers in March 2018 see Figure 6.8 Authors:
1 2
National Water Resources Hydrology Team
Source: Met Office Information produced by the Water Situation Forward Look group led by Environment Agency in partnership with the Centre for Ecology and Hydrology, British Geological Survey, Met Office (www.hydoutuk.net).
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© Environment Agency 2017
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Rainfall
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Figure 1.1: Monthly rainfall across England and Wales for the past 12 months. UKPP radar data (Source: Met Office © Crown Copyright, 2017). Note: Radar beam blockages in some regions may give anomalous totals in some areas. Crown copyright. All rights reserved. Environment Agency, 100026380, 2017.
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© Environment Agency 2017
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Figure 1.2: Total rainfall for hydrological areas across England for the current month (up to 31 August), the last 3 months, the last 6 months, and the last 12 months, classed relative to an analysis of respective historic totals. Final NCIC (National Climate Information Centre) data based on the Met Office 5km gridded rainfall dataset derived from rain gauges (Source: Met Office © Crown Copyright, 2017). Provisional data based on Environment Agency 1km gridded rainfall dataset derived from Environment Agency intensity rain gauges. Crown copyright. All rights reserved. Environment Agency, 100026380, 2017.
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© Environment Agency 2017
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Rainfall charts
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© Environment Agency 2017
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Figure 1.3: Monthly rainfall totals for the past 24 months as a percentage of the 1961 – 1990 long term average for each region and for England. NCIC (National Climate Information Centre) data. (Source: Met Office © Crown Copyright, 2017).
Soil moisture deficit End of July 20171
End of August 20172
Figure 2.1: Soil moisture deficits for weeks ending 1 August 2017 1 (left panel) and 29 August 2017 2 (right panel). Top row shows actual soil moisture deficits (mm) and bottom row shows the difference (mm) of the actual from the 1961-90 long term average soil moisture deficits. MORECS data for real land use (Source: Met Office © Crown Copyright, 2017). Crown copyright. All rights reserved. Environment Agency, 100026380, 2017
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Soil moisture deficit charts Central England 0
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Figure 2.2: Latest soil moisture deficits for all geographic regions compared to maximum, minimum and 1961-90 long term average. Weekly MORECS data for real land use. (Source: Met Office © Crown Copyright, 2017).
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© Environment Agency 2017
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River flows
^
“Naturalised” flows are provided for the River Thames at Kingston and the River Lee at Feildes Weir Underlined sites are regional index sites and are shown on the hydrographs in Figure 3.2
Figure 3.1: Monthly mean river flow for indicator sites for July and August 2017, expressed as a percentage of the respective long term average and classed relative to an analysis of historic July and August monthly means (Source: Environment Agency). Crown copyright. All rights reserved. Environment Agency, 100026380, 2017.
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River flow charts Exceptionally high Below normal ─ ─ ─ Monthly maximum
Notably high Notably low ─── Latest data
Above normal Exceptionally low ─ ─ ─ Monthly minimum
Offord, BEDFORD OUSE Ranking derived from data for the period Jan-1970 to Dec-2012
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Marston-on-Dove, DOVE Ranking derived from data for the period Jul-1965 to Dec-2012
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Figure 3.2: Index river flow sites for each geographic region. Monthly mean flow compared to an analysis of historic monthly mean flows, long term maximum and minimum flows. (Source: Environment Agency).
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© Environment Agency 2017
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Groundwater levels
^ The level at Priors Heyes remains high compared to historic levels because the aquifer is recovering from the effects of historic abstraction ^^ Sites are manually dipped at different times during the month. They may not be fully representative of levels at the month end Underlined sites are major aquifer index sites and are shown in the groundwater level charts in Figure 4.2
Figure 4.1: Groundwater levels for indicator sites at the end of July and August 2017, classed relative to an analysis of respective historic July and August levels (Source: Environment Agency). Geological map reproduced with kind permission from UK Groundwater Forum, BGS © NERC. Crown copyright. All rights reserved. Environment Agency, 100026380, 2017.
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© Environment Agency 2017
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Groundwater level charts Exceptionally high Below normal ─ ─ ─ Monthly maximum
Notably high Notably low ─── Latest data
Above normal Exceptionally low ─ ─ ─ Monthly minimum
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Heathlanes (Sandstone)
Ranking derived from data for the period Aug-1963 to Dec-2012
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Skirwith (Sandstone)
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Figure 4.2: Index groundwater level sites for major aquifers. End of month groundwater levels months compared to an analysis of historic end of month levels and long term maximum and minimum levels. (Source: Environment Agency, 2017).
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Reservoir storage
1. Engineering work at Abberton Reservoir in east England to increase capacity has been completed 2. Vyrnwy, Clywedog and Elan Valley reservoirs are located in Wales but provide a water resource to Central and north-west England 3. Current levels at Kielder will be deliberately lower than historical levels during a trial of a new flood alleviation control curve
Figure 5.1: Reservoir stocks at key individual and groups of reservoirs at the end of July and August 2017 as a percentage of total capacity and classed relative to an analysis of historic July and August values respectively (Source: Water Companies). Note: Classes shown may not necessarily relate to control curves or triggers for drought actions. As well as for public water supply, some reservoirs are drawn down to provide flood storage, river compensation flows or for reservoir safety inspections. In some cases current reservoir operating rules may differ from historic ones. Crown copyright. All rights reserved. Environment Agency, 100026380, 2017.
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© Environment Agency 2017
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East England
Central England
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Figure 5.2: Regional reservoir stocks. End of month reservoir stocks compared to long term maximum, minimum and average stocks (Source: Water Companies). Note: Historic records of individual reservoirs/reservoir groups making up the regional values vary in length.
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Forward look – river flow Rainfall greater than 120% LTA during September has occurred in 29 to 36% of years1 in the historic record (since 1910)
(a)
Rainfall greater than 100% LTA during September has occurred in 40 to 46% of years1 in the historic record (since 1910)
(b)
Rainfall less than 60% LTA during September has occurred in 21 to 29% of years1 in the historic record (since 1910)
Rainfall less than 80% LTA during September has occurred in 37 to 43% of years1 in the historic record (since 1910)
(c)
(d)
Figure 6.1: Projected river flows at key indicator sites up until the end of September 2017. Forecasts based on four scenarios: 120% (a), 100% (b), 80% (c) and 60% (d) of long term average rainfall during September 2017 (Source: Centre for Ecology and Hydrology, Environment Agency) 1
This range of probabilities is a regional analysis Projections for these sites are produced by CEH 3 Projections for these sites are produced by the Environment Agency ^ “Naturalised” flows are projected for these sites 2
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Rainfall greater than 120% LTA during Sep to Mar has occurred in 13 to 25% of years1 in the historic record (since 1910)
Rainfall greater than 100% LTA during Sep to Mar has occurred in 52 to 58% of years1 in the historic record (since 1910)
(b)
(a)
Rainfall less than 80% LTA during Sep to Mar has occurred in 8 to 15% of years1 in the historic record (since 1910)
(c)
Rainfall less than 60% LTA during Sep to Mar has occurred in 0 to 1% of years1 in the historic record (since 1910)
(d)
Figure 6.2: Projected river flows at key indicator sites up until the end of March 2018. Forecasts based on four scenarios: 120% (a), 100% (b), 80% (c) and 60% (d) of long term average rainfall between September 2017 and March 2018 (Source: Centre for Ecology and Hydrology, Environment Agency) 1
This range of probabilities is a regional analysis Projections for these sites are produced by CEH 3 Projections for these sites are produced by the Environment Agency ^ “Naturalised” flows are projected for these sites 2
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© Environment Agency 2017
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Exceptionally high or low levels are those which would typically occur 5% of the time within the historic record. Notably high or low levels are those which would typically occur 8% of the time. Above normal or below normal levels are those which would typically occur 15% of the time. Normal levels are those which would typically occur 44% of the time within the historic record.
Figure 6.3: Probabilistic ensemble projections of river flows at key indicator sites up until the end of September 2017. Pie charts indicate probability, based on climatology, of the surface water flow at each site being e.g. exceptionally low for the time of year. (Source: Centre for Ecology and Hydrology, Environment Agency). 1
Projections for these sites are produced by the Environment Agency Projections for these sites are produced by CEH ^“Naturalised” flows are projected for these sites 2
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© Environment Agency 2017
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Exceptionally high or low levels are those which would typically occur 5% of the time within the historic record. Notably high or low levels are those which would typically occur 8% of the time. Above normal or below normal levels are those which would typically occur 15% of the time. Normal levels are those which would typically occur 44% of the time within the historic record.
Figure 6.4: Probabilistic ensemble projections of river flows at key indicator sites up until the end of March 2018. Pie charts indicate probability, based on climatology, of the surface water flow at each site being e.g. exceptionally low for the time of year. (Source: Centre for Ecology and Hydrology, Environment Agency). 1
Projections for these sites are produced by the Environment Agency Projections for these sites are produced by CEH ^“Naturalised” flows are projected for these sites 2
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© Environment Agency 2017
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Forward look - groundwater Rainfall greater than 120% LTA during September has occurred in 29 to 36% of years1 in the historic record (since 1910)
Rainfall greater than 100% LTA during September has occurred in 40 to 46% of years1 in the historic record (since 1910)
(b)
(a)
Rainfall less than 80% LTA during September has occurred in 37 to 43% of years1 in the historic record (since 1910)
(c)
Rainfall less than 60% LTA during September has occurred in 21 to 29% of years1 in the historic record (since 1910)
(d)
Figure 6.5: Projected groundwater levels at key indicator sites at the end of September 2017. Forecasts based on four scenarios: 120% (a), 100% (b), 80% (c) and 60% (d) of long term average rainfall during September 2017 (Source: Environment Agency) Geological map reproduced with kind permission from UK Groundwater Forum BGS © NERC. Crown copyright all rights reserved. Environment Agency 100026380, 2017. * Projections for these sites are produced by BGS 1 This range of probabilities is a regional analysis
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© Environment Agency 2017
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Rainfall greater than 100% LTA during Sep to Mar has occurred in 52 to 58% of years1 in the historic record (since 1910)
Rainfall greater than 120% LTA during Sep to Mar has occurred in 13 to 25% of years1 in the historic record (since 1910)
(b)
(a)
Rainfall less than 80% LTA during Sep to Mar has occurred in 8 to 15% of years1 in the historic record (since 1910)
(c)
Rainfall less than 60% LTA during Sep to Mar has occurred in 0 to 1% of years1 in the historic record (since 1910)
(d)
Figure 6.6: Projected groundwater levels at key indicator sites at the end of March 2018. Forecasts based on four scenarios: 120% (a), 100% (b), 80% (c) and 60% (d) of long term average rainfall between September 2017 and March 2018 (Source: Environment Agency) Geological map reproduced with kind permission from UK Groundwater Forum BGS © NERC Crown copyright. All rights reserved. Environment Agency 100026380 2017. * Projections for these sites are produced by BGS 1 This range of probabilities is a regional analysis
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© Environment Agency 2017
19
Exceptionally high or low levels are those which would typically occur 5% of the time within the historic record. Notably high or low levels are those which would typically occur 8% of the time. Above normal or below normal levels are those which would typically occur 15% of the time. Normal levels are those which would typically occur 44% of the time within the historic record.
Figure 6.7: Probabilistic ensemble projections of groundwater levels at key indicator sites at the end of September 2017. Pie charts indicate probability, based on climatology, of the groundwater level at each site being e.g. exceptionally low for the time of year. (Source: Environment Agency) Geological map reproduced with kind permission from UK Groundwater Forum, BGS © NERC. Crown copyright. All rights reserved. Environment Agency, 100026380, 2017. * Projections for these sites are produced by BGS
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© Environment Agency 2017
20
Exceptionally high or low levels are those which would typically occur 5% of the time within the historic record. Notably high or low levels are those which would typically occur 8% of the time. Above normal or below normal levels are those which would typically occur 15% of the time. Normal levels are those which would typically occur 44% of the time within the historic record.
Figure 6.8: Probabilistic ensemble projections of groundwater levels at key indicator sites at the end of March 2018. Pie charts indicate probability, based on climatology, of the groundwater level at each site being e.g. exceptionally low for the time of year. (Source: Environment Agency) Geological map reproduced with kind permission from UK Groundwater Forum, BGS © NERC. Crown copyright. All rights reserved. Environment Agency, 100026380, 2017. * Projections for these sites are produced by BGS
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© Environment Agency 2017
21
Figure 7.1: Geographic regions Crown copyright. All rights reserved. Environment Agency, 100026380, 2017.
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© Environment Agency 2017
22
Glossary Term
Definition
Aquifer
A geological formation able to store and transmit water.
Areal average rainfall
The estimated average depth of rainfall over a defined area. Expressed in depth of water (mm).
Artesian
The condition where the groundwater level is above ground surface but is prevented from rising to this level by an overlying continuous low permeability layer, such as clay.
Artesian borehole
Borehole where the level of groundwater is above the top of the borehole and groundwater flows out of the borehole when unsealed.
Cumecs
Cubic metres per second (m 3s-1)
Effective rainfall
The rainfall available to percolate into the soil or produce river flow. Expressed in depth of water (mm).
Flood Alert/Flood Warning
Three levels of warnings may be issued by the Environment Agency. Flood Alerts indicate flooding is possible. Flood Warnings indicate flooding is expected. Severe Flood Warnings indicate severe flooding.
Groundwater
The water found in an aquifer.
Long term average (LTA)
The arithmetic mean, calculated from the historic record. For rainfall and soil moisture deficit, the period refers to 1961-1990, unless otherwise stated. For other parameters, the period may vary according to data availability
mAOD
Metres Above Ordnance Datum (mean sea level at Newlyn Cornwall).
MORECS
Met Office Rainfall and Evaporation Calculation System. Met Office service providing real time calculation of evapotranspiration, soil moisture deficit and effective rainfall on a 40 x 40 km grid.
Naturalised flow
River flow with the impacts of artificial influences removed. Artificial influences may include abstractions, discharges, transfers, augmentation and impoundments.
NCIC
National Climate Information Centre. NCIC area monthly rainfall totals are derived using the Met Office 5 km gridded dataset, which uses rain gauge observations.
Recharge
The process of increasing the water stored in the saturated zone of an aquifer. Expressed in depth of water (mm).
Reservoir gross capacity
The total capacity of a reservoir.
Reservoir live capacity
The capacity of the reservoir that is normally usable for storage to meet established reservoir operating requirements. This excludes any capacity not available for use (e.g. storage held back for emergency services, operating agreements or physical restrictions). May also be referred to as ‘net’ or ‘deployable’ capacity.
Soil moisture deficit (SMD)
The difference between the amount of water actually in the soil and the amount of water the soil can hold. Expressed in depth of water (mm).
Categories Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low
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Value likely to fall within this band 5% of the time Value likely to fall within this band 8% of the time Value likely to fall within this band 15% of the time Value likely to fall within this band 44% of the time Value likely to fall within this band 15% of the time Value likely to fall within this band 8% of the time Value likely to fall within this band 5% of the time
Rainfall August rainfall was highest in north-west England and lowest across parts of east and north-east England, with totals ranging from 170mm in parts of Cumbria to approximately 40mm across parts of Lincolnshire, Norfolk and Northumbria. Rainfall totals were above the long term average (LTA) for August across two-thirds of hydrological areas, with parts of Kent and West Sussex receiving just over 150% of the August LTA. (Figure 1.1). August rainfall totals were classed as normal or higher for the time of year across almost all of the hydrological areas. Cumulative rainfall totals for the past 3 months range from normal to notably high for the time of year across the whole of England. In contrast, cumulative rainfall totals for the past 12 months still show a rainfall deficit with most of England being below normal or notably low for the time of year (Figure 1.2). At a regional scale, August rainfall totals ranged from 99% of the LTA in north-east England to 126% in south-east England and were normal for the time of year across all regions. The monthly rainfall total for England was 105% of the 1961-90 LTA for August (108% of the 1981-2010 LTA) (Figure 1.3).
Soil moisture deficit Despite the above average August rainfall across much of England, soil moisture deficits (SMDs) generally increased during August. At the end of August, soils were drier than at the end of July across nearly two-thirds of England, with SMDs ranging from approximately 1mm in parts of north-west England to nearly 160mm across parts of Norfolk and Cambridgeshire. Soils were drier than the August LTA across much of central and east England in particular, but wetter than average elsewhere, particularly across parts of Devon and Cornwall (Figure 2.1). At a regional scale, soils were drier at the end of August compared to the end of July across all regions, with end of month SMDs ranging from 29mm in north-west England to 99mm in east England. Soils were drier than the LTA in east and central England but wetter elsewhere (Figure 2.2).
River flows Compared with July, monthly mean river flows for August increased at just over two-thirds of indicator sites across England. River flows were classed as normal or higher for the time of year at all but 3 indicator sites; flows in the rivers Itchen and Eastern Rother were below normal for the time of year whilst the River Coln remained exceptionally low for the second consecutive month. Flows at all indicator sites in north-west England were above normal for the time of year, with the River Derwent being notably high (Figure 3.1). At the regional index sites, monthly mean river flows were normal for the time of year at 4 of the 6 sites, whilst the River Lune in north-west England and the Bedford Ouse in east England were above normal (Figure 3.2).
All data are provisional and may be subject to revision. The views expressed in this document are not necessarily those of the Environment Agency. Its officers, servants or agents accept no liability for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained herein.
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© Environment Agency 2017
1
Groundwater levels Groundwater levels decreased during August at all but 3 of the indicator sites – levels at Wetwang (Hull and East Riding chalk aquifer), Crow Lady Farm (Fylde and Preston sandstone aquifer) and Woodyates (Upper Dorset Stour chalk aquifer) all increased slightly compared to the end of July. End of month groundwater levels were below normal or lower for the time of year at half of the indicator sites, with Ashley Green (Chilterns East chalk aquifer) and Little Bucket (East Kent Stour chalk aquifer) both remaining exceptionally low for the third consecutive month. End of month groundwater levels at the major aquifer index sites ranged from exceptionally low for the time of year at Little Bucket (East Kent Stour chalk aquifer) to normal for the time of year at Heathlanes (Shropshire sandstone aquifer), Dalton Holme (Hull and East Riding chalk aquifer) and Skirwith (Carlisle Basin and Eden Valley sandstone aquifer) (Figures 4.1 and 4.2).
Reservoir storage Reservoir stocks decreased at just over half of the reported reservoirs or reservoir groups during August. Notable decreases occurred at Carsington and Ogston (9%), Bough Beech (9%) and Chew Valley (12%) reservoirs, whilst Clywedog reservoir increased by 11%. End of month stocks were classed as normal or higher for the time of year at nearly three-quarters of all reported reservoirs and reservoir groups. The remaining sites were classed as below normal or notably low for the time of year (Figure 5.1). Compared with the end of July, regional reservoir stocks increased in north-west and central England by 4% and 2% respectively and decreased elsewhere by up to 3%. End of August stocks ranged from 67% of total capacity in south-west England to 87% in east England. Overall storage for England decreased slightly to 79% of total capacity (Figure 5.2).
Forward look The first half of September is likely to see a mix of clear spells and heavy showers across most of the country. The second half of September is likely to see more settled spells – especially in the south, south-east and west of the country. For the 3-month period September to November above-average rainfall is considered slightly more probable than below-average rainfall but the forecast is uncertain1. Projections for river flows at key sites2 Two-thirds of the modelled sites have a greater than expected chance of cumulative river flows being below normal or lower by both the end of September 2017 and the end of March 2018. For scenario based projections of cumulative river flows at key sites by September 2017 see Figure 6.1 For scenario based projections of cumulative river flows at key sites by March 2018 see Figure 6.2 For probabilistic ensemble projections of cumulative river flows at key sites by September 2017 see Figure 6.3 For probabilistic ensemble projections of cumulative river flows at key sites by March 2018 see Figure 6.4 Projections for groundwater levels in key aquifers2 Half of the modelled sites have a greater than expected chance of below normal or lower groundwater levels for the time of year at the end of September 2017. By March 2018, just over a third of all modelled sites have a greater than expected chance of notably low or lower groundwater levels for the time of year. For scenario based projections of groundwater levels in key aquifers in September 2017 see Figure 6.5 For scenario based projections of groundwater levels in key aquifers in March 2018 see Figure 6.6 For probabilistic ensemble projections of groundwater levels in key aquifers in September 2017 see Figure 6.7 For probabilistic ensemble projections of groundwater levels in key aquifers in March 2018 see Figure 6.8 Authors:
1 2
National Water Resources Hydrology Team
Source: Met Office Information produced by the Water Situation Forward Look group led by Environment Agency in partnership with the Centre for Ecology and Hydrology, British Geological Survey, Met Office (www.hydoutuk.net).
www.gov.uk/environment-agency
© Environment Agency 2017
2
Rainfall
September 2016
October 2016
November 2016
December 2016
January 2017
February 2017
March 2017
April 2017
May 2017
June 2017
July 2017
August 2017
Figure 1.1: Monthly rainfall across England and Wales for the past 12 months. UKPP radar data (Source: Met Office © Crown Copyright, 2017). Note: Radar beam blockages in some regions may give anomalous totals in some areas. Crown copyright. All rights reserved. Environment Agency, 100026380, 2017.
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© Environment Agency 2017
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Figure 1.2: Total rainfall for hydrological areas across England for the current month (up to 31 August), the last 3 months, the last 6 months, and the last 12 months, classed relative to an analysis of respective historic totals. Final NCIC (National Climate Information Centre) data based on the Met Office 5km gridded rainfall dataset derived from rain gauges (Source: Met Office © Crown Copyright, 2017). Provisional data based on Environment Agency 1km gridded rainfall dataset derived from Environment Agency intensity rain gauges. Crown copyright. All rights reserved. Environment Agency, 100026380, 2017.
www.gov.uk/environment-agency
© Environment Agency 2017
4
Rainfall charts
Below average rainfall Above average rainfall
300%
Central England East England
300%
250%
250%
200%
200%
150%
150%
100%
100%
50%
50%
0%
0%
Feb-17
Mar-17
Apr-17
May-17
Jun-17
Jul-17
Aug-17
Feb-17
Mar-17
Apr-17
May-17
Jun-17
Jul-17
Aug-17
Dec-16
Jan-17
Feb-17
Mar-17
Apr-17
May-17
Jun-17
Jul-17
Aug-17
Sep-15
Oct-15
Nov-15
Dec-15
Jan-16
Feb-16
Mar-16
Apr-16
May-16
Jun-16
Jul-16
Aug-16
Sep-16
Oct-16
Nov-16
Dec-16
Jan-17
Feb-17
Mar-17
Apr-17
May-17
Jun-17
Jul-17
Aug-17
Sep-15
Oct-15
Nov-15
Dec-15
Jan-16
Feb-16
Mar-16
Apr-16
May-16
Jun-16
Jul-16
Aug-16
Sep-16
Oct-16
Nov-16
Jan-17
Nov-16
Jan-17
Nov-16
0%
Oct-16
0%
Sep-16
50%
Aug-16
50%
Jul-16
100%
Jun-16
100%
Dec-16
South-west England South-east England
May-16
150%
Apr-16
150%
Mar-16
200%
Feb-16
200%
Jan-16
250%
Dec-15
250%
Nov-15
300%
Oct-15 Sep-15
Aug-17 Jul-17 Jun-17 May-17 Apr-17 Mar-17 Feb-17 Jan-17
Dec-16 Nov-16 Oct-16 Sep-16 Aug-16
Jul-16 Jun-16 May-16 Apr-16
Mar-16 Feb-16 Jan-16 Dec-15 Nov-15
Oct-15 Sep-15
300%
Oct-16
0%
Sep-16
0%
Aug-16
50%
Jul-16
50%
Jun-16
100%
May-16
100%
Apr-16
150%
Mar-16
150%
Feb-16
200%
Jan-16
200%
Dec-15
250%
Nov-15
250%
Oct-15 Sep-15
Aug-17 Jul-17 Jun-17 May-17 Apr-17 Mar-17 Feb-17 Jan-17
300%
Dec-16
North-west England North-east England
Aug-17
Jul-17
Jun-17
May-17
Apr-17
Mar-17
Feb-17
Jan-17
Dec-16
Nov-16
Oct-16
Sep-16
Aug-16
Jul-16
Jun-16
May-16
Apr-16
Mar-16
Feb-16
Jan-16
Dec-15
Nov-15
Oct-15
Sep-15
5
© Environment Agency 2017
www.gov.uk/environment-agency
Dec-16 Nov-16 Oct-16 Sep-16 Aug-16
Jul-16 Jun-16 May-16 Apr-16
Mar-16 Feb-16 Jan-16 Dec-15 Nov-15
Oct-15 Sep-15
300%
300%
England
250%
200%
150%
100%
50%
0%
Figure 1.3: Monthly rainfall totals for the past 24 months as a percentage of the 1961 – 1990 long term average for each region and for England. NCIC (National Climate Information Centre) data. (Source: Met Office © Crown Copyright, 2017).
Soil moisture deficit End of July 20171
End of August 20172
Figure 2.1: Soil moisture deficits for weeks ending 1 August 2017 1 (left panel) and 29 August 2017 2 (right panel). Top row shows actual soil moisture deficits (mm) and bottom row shows the difference (mm) of the actual from the 1961-90 long term average soil moisture deficits. MORECS data for real land use (Source: Met Office © Crown Copyright, 2017). Crown copyright. All rights reserved. Environment Agency, 100026380, 2017
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© Environment Agency 2017
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Soil moisture deficit charts Central England 0
10
10
20
20
Soil moisture deficit (mm)
Soil moisture deficit (mm)
East England 0
30 40 50 60 70 80 90
30 40 50 60 70 80 90
100
100
110
110
120
120
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130
140
140 Apr
May
Jun
Jul
Aug
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Jan
Feb Mar
Apr
May
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Apr
May
Jun
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0
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Feb Mar
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South-east England
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Dec
Jan
Feb Mar
Apr
South-west England
0
0
10
10
20
20
30
Soil moisture deficit (mm)
Soil moisture deficit (mm)
Dec
North-west England
0
Soil moisture deficit (mm)
Soil moisture deficit (mm)
North-east England
Nov
40
50 60 70 80 90 100 110
30 40 50 60 70 80 90 100
120
110
130
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140
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150
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140 Apr
May
Jun
Jul
Aug
Sep
Oct
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Below minimum monthly level
Apr
May
Jun
Jul
Aug
Sep
Above maximum monthly level
Apr
May
────
Jun
Jul
Aug
Sep
Average
Oct
Nov
Dec
Jan
Feb Mar
────
Apr
Latest data
Figure 2.2: Latest soil moisture deficits for all geographic regions compared to maximum, minimum and 1961-90 long term average. Weekly MORECS data for real land use. (Source: Met Office © Crown Copyright, 2017).
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© Environment Agency 2017
7
River flows
^
“Naturalised” flows are provided for the River Thames at Kingston and the River Lee at Feildes Weir Underlined sites are regional index sites and are shown on the hydrographs in Figure 3.2
Figure 3.1: Monthly mean river flow for indicator sites for July and August 2017, expressed as a percentage of the respective long term average and classed relative to an analysis of historic July and August monthly means (Source: Environment Agency). Crown copyright. All rights reserved. Environment Agency, 100026380, 2017.
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© Environment Agency 2017
8
River flow charts Exceptionally high Below normal ─ ─ ─ Monthly maximum
Notably high Notably low ─── Latest data
Above normal Exceptionally low ─ ─ ─ Monthly minimum
Offord, BEDFORD OUSE Ranking derived from data for the period Jan-1970 to Dec-2012
Normal
Marston-on-Dove, DOVE Ranking derived from data for the period Jul-1965 to Dec-2012
120 50
Flow (cumecs)
Flow (cumecs)
100 80
60 40
30 20 10
20 0 Nov-16
40
Jan-17
Mar-17
May-17
Jul-17
0 Nov-16
Sep-17
Haydon Bridge, SOUTH TYNE Ranking derived from data for the period Oct-1974 to Dec-2012
Jan-17
Mar-17
May-17
Jul-17
Sep-17
Caton, LUNE Ranking derived from data for the period Jan-1959 to Dec-2012 140 120
50
Flow (cumecs)
Flow (cumecs)
60
40 30 20 10 0 Nov-16
100 80 60 40 20
Jan-17
Mar-17
May-17
Jul-17
0 Nov-16
Sep-17
Horton, GREAT STOUR Ranking derived from data for the period Oct-1964 to Dec-2012
Jan-17
Mar-17
May-17
Jul-17
Sep-17
Kingston, THAMES Ranking derived from data for the period Jan-1883 to Dec-2012
16
350
300
12
Flow (cumecs)
Flow (cumecs)
14
10 8 6 4
200 150 100 50
2 0 Nov-16
250
Jan-17
Mar-17
May-17
Jul-17
0 Nov-16
Sep-17
Jan-17
Mar-17
May-17
Jul-17
Sep-17
Thorverton, EXE Ranking derived from data for the period Apr-1956 to Dec-2012 70
Flow (cumecs)
60 50 40
30 20 10 0 Nov-16
Jan-17
Mar-17
May-17
Jul-17
Sep-17
Figure 3.2: Index river flow sites for each geographic region. Monthly mean flow compared to an analysis of historic monthly mean flows, long term maximum and minimum flows. (Source: Environment Agency).
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© Environment Agency 2017
9
Groundwater levels
^ The level at Priors Heyes remains high compared to historic levels because the aquifer is recovering from the effects of historic abstraction ^^ Sites are manually dipped at different times during the month. They may not be fully representative of levels at the month end Underlined sites are major aquifer index sites and are shown in the groundwater level charts in Figure 4.2
Figure 4.1: Groundwater levels for indicator sites at the end of July and August 2017, classed relative to an analysis of respective historic July and August levels (Source: Environment Agency). Geological map reproduced with kind permission from UK Groundwater Forum, BGS © NERC. Crown copyright. All rights reserved. Environment Agency, 100026380, 2017.
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© Environment Agency 2017
10
Groundwater level charts Exceptionally high Below normal ─ ─ ─ Monthly maximum
Notably high Notably low ─── Latest data
Above normal Exceptionally low ─ ─ ─ Monthly minimum
Normal
Redlands Hall (Chalk)
Heathlanes (Sandstone)
Ranking derived from data for the period Aug-1963 to Dec-2012
Ranking derived from data for the period Jul-1971 to Dec-2012
66
56
65
Level (mAOD)
Level (mAOD)
51 46 41 36
64 63 62
61 60
31 Nov-15 Feb-16 May-16 Aug-16 Nov-16 Feb-17 May-17 Aug-17
59 Nov-15 Feb-16 May-16 Aug-16 Nov-16 Feb-17 May-17 Aug-17
Dalton Holme (Chalk)
Skirwith (Sandstone)
Ranking derived from data for the period Jan-1889 to Dec-2012
Ranking derived from data for the period Oct-1978 to Dec-2012
133
25
132
21
Level (mAOD)
Level (mAOD)
23
19 17 15 13
131 130 129
11 128 Nov-15 Feb-16 May-16 Aug-16 Nov-16 Feb-17 May-17 Aug-17
9 Nov-15 Feb-16 May-16 Aug-16 Nov-16 Feb-17 May-17 Aug-17
Chilgrove (Chalk)
Little Bucket (Chalk)
Ranking derived from data for the period Feb-1836 to Dec-2012
Ranking derived from data for the period Jan-1971 to Dec-2012
77
85 80
67
Level (mAOD)
Level (mAOD)
72
62 57 52 47 42
70 65 60
37
55 Nov-15 Feb-16 May-16 Aug-16 Nov-16 Feb-17 May-17 Aug-17
32 Nov-15 Feb-16 May-16 Aug-16 Nov-16 Feb-17 May-17 Aug-17
Jackaments Bottom (Jurassic Limestone)
Stonor Park (Chalk)
Ranking derived from data for the period Jan-1974 to Dec-2012
Ranking derived from data for the period May-1961 to Dec-2012
107
90
103 101 99 97
Level (mAOD)
105
Level (mAOD)
75
85
80 75
70
95 93 91 Nov-15 Feb-16 May-16 Aug-16 Nov-16 Feb-17 May-17 Aug-17
65
60 Nov-15 Feb-16 May-16 Aug-16 Nov-16 Feb-17 May-17 Aug-17
Figure 4.2: Index groundwater level sites for major aquifers. End of month groundwater levels months compared to an analysis of historic end of month levels and long term maximum and minimum levels. (Source: Environment Agency, 2017).
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© Environment Agency 2017
11
Reservoir storage
1. Engineering work at Abberton Reservoir in east England to increase capacity has been completed 2. Vyrnwy, Clywedog and Elan Valley reservoirs are located in Wales but provide a water resource to Central and north-west England 3. Current levels at Kielder will be deliberately lower than historical levels during a trial of a new flood alleviation control curve
Figure 5.1: Reservoir stocks at key individual and groups of reservoirs at the end of July and August 2017 as a percentage of total capacity and classed relative to an analysis of historic July and August values respectively (Source: Water Companies). Note: Classes shown may not necessarily relate to control curves or triggers for drought actions. As well as for public water supply, some reservoirs are drawn down to provide flood storage, river compensation flows or for reservoir safety inspections. In some cases current reservoir operating rules may differ from historic ones. Crown copyright. All rights reserved. Environment Agency, 100026380, 2017.
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© Environment Agency 2017
12
East England
Central England
Based on storage in Abberton, Grafham, Hanningfield, Rutland reservoirs
Based on storage in Clywedog, Carsington and Ogston, Derwent Valley, Dove (Foremark & Staunton), Draycote, Elan Valley Group reservoirs
100
100
90
90
Percentage of total capacity
Percentage of total capacity
Reservoir storage charts
80 70 60 50 40
60 50 40 30
20
20
10
10 0
Feb Mar
Apr May Jun
Jul
Aug Sep Oct
Nov Dec Jan
Feb Mar
Apr May Jun
Jul
Aug Sep
Feb Mar
Apr May Jun
Jul
Aug Sep Oct
Nov Dec Jan
Feb Mar
Apr May Jun
Jul
North-east England
North-west England
Based on storage in Kielder, Teesdale Group, Yorkshire Supply Group reservoirs
Based on storage in NCZ Regional Group, Pennines Group, Vyrnwy reservoirs
100
100
90
90
Percentage of total capacity
Percentage of total capacity
70
30
0
80 70 60 50 40
Aug Sep
80 70 60 50 40
30
30
20
20
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10
0
0 Feb Mar
Apr May Jun
Jul
Aug Sep Oct
Nov Dec Jan
Feb Mar
Apr May Jun
Jul
Aug Sep
Feb Mar
Apr May Jun
Jul
Aug Sep Oct
Nov Dec Jan
Feb Mar
Apr May Jun
Jul
Aug Sep
South-east England
South-west England
Based on storage in Ardingly, Bewl, Bough Beech, Farmoor, Lower Lee Group, Lower Thames Group reservoirs
Based on storage in Blagdon, Chew Valley, Clatworthy, Colliford, Roadford, Stithians, Wimbleball reservoirs
100
100
90
90
Percentage of total capacity
Percentage of total capacity
80
80 70 60 50 40
80 70 60 50 40
30
30
20
20
10
10
0
0 Feb Mar
Apr May Jun
Jul
Aug Sep Oct
Nov Dec Jan
Feb Mar
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Apr May Jun
Jul
Aug Sep Oct
Nov Dec Jan
Feb Mar
Apr May Jun
Jul
Aug Sep
England Based on combined regional storage 100
Percentage of total capacity
90 80 70 60 50 40 30 20 10 0 Feb Mar
Below minimum monthly level
Apr May Jun
Jul
Aug Sep Oct
Above maximum monthly level
Nov Dec Jan
Feb Mar
Apr May Jun
────
Jul
Aug Sep
Average
────
Latest data
Figure 5.2: Regional reservoir stocks. End of month reservoir stocks compared to long term maximum, minimum and average stocks (Source: Water Companies). Note: Historic records of individual reservoirs/reservoir groups making up the regional values vary in length.
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© Environment Agency 2017
13
Forward look – river flow Rainfall greater than 120% LTA during September has occurred in 29 to 36% of years1 in the historic record (since 1910)
(a)
Rainfall greater than 100% LTA during September has occurred in 40 to 46% of years1 in the historic record (since 1910)
(b)
Rainfall less than 60% LTA during September has occurred in 21 to 29% of years1 in the historic record (since 1910)
Rainfall less than 80% LTA during September has occurred in 37 to 43% of years1 in the historic record (since 1910)
(c)
(d)
Figure 6.1: Projected river flows at key indicator sites up until the end of September 2017. Forecasts based on four scenarios: 120% (a), 100% (b), 80% (c) and 60% (d) of long term average rainfall during September 2017 (Source: Centre for Ecology and Hydrology, Environment Agency) 1
This range of probabilities is a regional analysis Projections for these sites are produced by CEH 3 Projections for these sites are produced by the Environment Agency ^ “Naturalised” flows are projected for these sites 2
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© Environment Agency 2017
14
Rainfall greater than 120% LTA during Sep to Mar has occurred in 13 to 25% of years1 in the historic record (since 1910)
Rainfall greater than 100% LTA during Sep to Mar has occurred in 52 to 58% of years1 in the historic record (since 1910)
(b)
(a)
Rainfall less than 80% LTA during Sep to Mar has occurred in 8 to 15% of years1 in the historic record (since 1910)
(c)
Rainfall less than 60% LTA during Sep to Mar has occurred in 0 to 1% of years1 in the historic record (since 1910)
(d)
Figure 6.2: Projected river flows at key indicator sites up until the end of March 2018. Forecasts based on four scenarios: 120% (a), 100% (b), 80% (c) and 60% (d) of long term average rainfall between September 2017 and March 2018 (Source: Centre for Ecology and Hydrology, Environment Agency) 1
This range of probabilities is a regional analysis Projections for these sites are produced by CEH 3 Projections for these sites are produced by the Environment Agency ^ “Naturalised” flows are projected for these sites 2
www.gov.uk/environment-agency
© Environment Agency 2017
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Exceptionally high or low levels are those which would typically occur 5% of the time within the historic record. Notably high or low levels are those which would typically occur 8% of the time. Above normal or below normal levels are those which would typically occur 15% of the time. Normal levels are those which would typically occur 44% of the time within the historic record.
Figure 6.3: Probabilistic ensemble projections of river flows at key indicator sites up until the end of September 2017. Pie charts indicate probability, based on climatology, of the surface water flow at each site being e.g. exceptionally low for the time of year. (Source: Centre for Ecology and Hydrology, Environment Agency). 1
Projections for these sites are produced by the Environment Agency Projections for these sites are produced by CEH ^“Naturalised” flows are projected for these sites 2
www.gov.uk/environment-agency
© Environment Agency 2017
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Exceptionally high or low levels are those which would typically occur 5% of the time within the historic record. Notably high or low levels are those which would typically occur 8% of the time. Above normal or below normal levels are those which would typically occur 15% of the time. Normal levels are those which would typically occur 44% of the time within the historic record.
Figure 6.4: Probabilistic ensemble projections of river flows at key indicator sites up until the end of March 2018. Pie charts indicate probability, based on climatology, of the surface water flow at each site being e.g. exceptionally low for the time of year. (Source: Centre for Ecology and Hydrology, Environment Agency). 1
Projections for these sites are produced by the Environment Agency Projections for these sites are produced by CEH ^“Naturalised” flows are projected for these sites 2
www.gov.uk/environment-agency
© Environment Agency 2017
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Forward look - groundwater Rainfall greater than 120% LTA during September has occurred in 29 to 36% of years1 in the historic record (since 1910)
Rainfall greater than 100% LTA during September has occurred in 40 to 46% of years1 in the historic record (since 1910)
(b)
(a)
Rainfall less than 80% LTA during September has occurred in 37 to 43% of years1 in the historic record (since 1910)
(c)
Rainfall less than 60% LTA during September has occurred in 21 to 29% of years1 in the historic record (since 1910)
(d)
Figure 6.5: Projected groundwater levels at key indicator sites at the end of September 2017. Forecasts based on four scenarios: 120% (a), 100% (b), 80% (c) and 60% (d) of long term average rainfall during September 2017 (Source: Environment Agency) Geological map reproduced with kind permission from UK Groundwater Forum BGS © NERC. Crown copyright all rights reserved. Environment Agency 100026380, 2017. * Projections for these sites are produced by BGS 1 This range of probabilities is a regional analysis
www.gov.uk/environment-agency
© Environment Agency 2017
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Rainfall greater than 100% LTA during Sep to Mar has occurred in 52 to 58% of years1 in the historic record (since 1910)
Rainfall greater than 120% LTA during Sep to Mar has occurred in 13 to 25% of years1 in the historic record (since 1910)
(b)
(a)
Rainfall less than 80% LTA during Sep to Mar has occurred in 8 to 15% of years1 in the historic record (since 1910)
(c)
Rainfall less than 60% LTA during Sep to Mar has occurred in 0 to 1% of years1 in the historic record (since 1910)
(d)
Figure 6.6: Projected groundwater levels at key indicator sites at the end of March 2018. Forecasts based on four scenarios: 120% (a), 100% (b), 80% (c) and 60% (d) of long term average rainfall between September 2017 and March 2018 (Source: Environment Agency) Geological map reproduced with kind permission from UK Groundwater Forum BGS © NERC Crown copyright. All rights reserved. Environment Agency 100026380 2017. * Projections for these sites are produced by BGS 1 This range of probabilities is a regional analysis
www.gov.uk/environment-agency
© Environment Agency 2017
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Exceptionally high or low levels are those which would typically occur 5% of the time within the historic record. Notably high or low levels are those which would typically occur 8% of the time. Above normal or below normal levels are those which would typically occur 15% of the time. Normal levels are those which would typically occur 44% of the time within the historic record.
Figure 6.7: Probabilistic ensemble projections of groundwater levels at key indicator sites at the end of September 2017. Pie charts indicate probability, based on climatology, of the groundwater level at each site being e.g. exceptionally low for the time of year. (Source: Environment Agency) Geological map reproduced with kind permission from UK Groundwater Forum, BGS © NERC. Crown copyright. All rights reserved. Environment Agency, 100026380, 2017. * Projections for these sites are produced by BGS
www.gov.uk/environment-agency
© Environment Agency 2017
20
Exceptionally high or low levels are those which would typically occur 5% of the time within the historic record. Notably high or low levels are those which would typically occur 8% of the time. Above normal or below normal levels are those which would typically occur 15% of the time. Normal levels are those which would typically occur 44% of the time within the historic record.
Figure 6.8: Probabilistic ensemble projections of groundwater levels at key indicator sites at the end of March 2018. Pie charts indicate probability, based on climatology, of the groundwater level at each site being e.g. exceptionally low for the time of year. (Source: Environment Agency) Geological map reproduced with kind permission from UK Groundwater Forum, BGS © NERC. Crown copyright. All rights reserved. Environment Agency, 100026380, 2017. * Projections for these sites are produced by BGS
www.gov.uk/environment-agency
© Environment Agency 2017
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Figure 7.1: Geographic regions Crown copyright. All rights reserved. Environment Agency, 100026380, 2017.
www.gov.uk/environment-agency
© Environment Agency 2017
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Glossary Term
Definition
Aquifer
A geological formation able to store and transmit water.
Areal average rainfall
The estimated average depth of rainfall over a defined area. Expressed in depth of water (mm).
Artesian
The condition where the groundwater level is above ground surface but is prevented from rising to this level by an overlying continuous low permeability layer, such as clay.
Artesian borehole
Borehole where the level of groundwater is above the top of the borehole and groundwater flows out of the borehole when unsealed.
Cumecs
Cubic metres per second (m 3s-1)
Effective rainfall
The rainfall available to percolate into the soil or produce river flow. Expressed in depth of water (mm).
Flood Alert/Flood Warning
Three levels of warnings may be issued by the Environment Agency. Flood Alerts indicate flooding is possible. Flood Warnings indicate flooding is expected. Severe Flood Warnings indicate severe flooding.
Groundwater
The water found in an aquifer.
Long term average (LTA)
The arithmetic mean, calculated from the historic record. For rainfall and soil moisture deficit, the period refers to 1961-1990, unless otherwise stated. For other parameters, the period may vary according to data availability
mAOD
Metres Above Ordnance Datum (mean sea level at Newlyn Cornwall).
MORECS
Met Office Rainfall and Evaporation Calculation System. Met Office service providing real time calculation of evapotranspiration, soil moisture deficit and effective rainfall on a 40 x 40 km grid.
Naturalised flow
River flow with the impacts of artificial influences removed. Artificial influences may include abstractions, discharges, transfers, augmentation and impoundments.
NCIC
National Climate Information Centre. NCIC area monthly rainfall totals are derived using the Met Office 5 km gridded dataset, which uses rain gauge observations.
Recharge
The process of increasing the water stored in the saturated zone of an aquifer. Expressed in depth of water (mm).
Reservoir gross capacity
The total capacity of a reservoir.
Reservoir live capacity
The capacity of the reservoir that is normally usable for storage to meet established reservoir operating requirements. This excludes any capacity not available for use (e.g. storage held back for emergency services, operating agreements or physical restrictions). May also be referred to as ‘net’ or ‘deployable’ capacity.
Soil moisture deficit (SMD)
The difference between the amount of water actually in the soil and the amount of water the soil can hold. Expressed in depth of water (mm).
Categories Exceptionally high Notably high Above normal Normal Below normal Notably low Exceptionally low
www.gov.uk/environment-agency
Value likely to fall within this band 5% of the time Value likely to fall within this band 8% of the time Value likely to fall within this band 15% of the time Value likely to fall within this band 44% of the time Value likely to fall within this band 15% of the time Value likely to fall within this band 8% of the time Value likely to fall within this band 5% of the time
