Two dry winters led to significant water resource concerns and the real possibility of affecting the 2012 Olympic Games. The rapid termination of drought instead lead to widespread flooding.
Across most of the UK, the 2010/2012 period was remarkable in climatic terms with exceptional departures from normal rainfall, runoff and aquifer recharge patterns. Generalising broadly, drought conditions developed through 2010, intensified during 2011 and were severe across much of England & Wales by the early spring of 2012. Record late spring and summer rainfall then triggered a hydrological transformation that has no close modern parallel. Seasonally extreme river flows were common through the summer, heralding further extensive flooding during the autumn and, particularly, the early winter when record runoff at the national scale provided a culmination to the wettest nine-month sequence for England & Wales in an instrumental record beginning in 1766.
Audio: Recollections of the 2010-2012 Drought from a Western Isles Whisky Distillery
At the beginning of 2010, the water situation appeared healthy, following on from a wet summer in 2009 and a slightly wetter than average autumn. Rainfall in the winter of 2009/2010 was above average in eastern areas of the UK, and hence soil moisture deficits remained small and water stocks healthy, until we came to spring 2010 which was much drier than average across the whole of the UK.
Rainfall during the summer and autumn of 2010 was not far from average generally, but it was the recharge period following that that gave cause for concern as rainfall was rather below average in the winter, and then a long way below average through the spring of 2011 over England & Wales, allowing soil moisture deficits to grow rapidly. After a slightly wetter than average summer in some areas, the autumn of 2011 was again drier than average over England & Wales especially, delaying the beginning of the recharge’season. The winter of 2011/2012 was again rather dry for most of England & Wales, and therefore by this time water availability was well below average, especially as March 2012 was also dry, as we went into spring. However, there was a dramatic transformation after that, with record-breaking amounts of rainfall across parts of the UK during April, June and July 2012 amid a succession of rather wet months, thus ending drought concerns.
The plot below shows the monthly North Atlantic Oscillation (NAO) Index for the periods before, during and after the drought. The NAO is a prominent teleconnection pattern in all seasons, and strong positive phases tend to be associationed with above-average temperatures in northern Europe, whilst negative phases of the NAO tend to be associated with below-average temperatures. There is more information available here.
The drought began in the north-west and central England in early 2010 and initially affected western parts of England and Wales. Drought conditions developed further south and east later in the year and were mostly limited to England and Wales throughout the event. Following its peak in March 2012, throughout the UK the drought was terminated rapidly through the spring and summer of 2012. Drought deficiencies and spatial extent rapidly decreased from spring 2012 onwards, resulting in a number of severe flood episodes.
In general, the events’ two-year duration ranked only moderately amongst all previous historical events, as do the accumulated deficits. For south-east England where hosepipe bans were implemented, durations and accumulated deficits for the drought ranked only on the periphery of or outside the top ten of all previous historical events. The exception to this was southern and central England and Wales, where drought duration and severity both ranked amongst the top three compared to all previous events. More notable was the intensity of drought conditions; drought minima were amongst the lowest ever experienced to date in parts of Wales, East Anglia and southern England. The combination of only moderate duration but the high intensity is related to rainfall deficiencies that were particularly acute during the winter months of both years. The termination of drought conditions through the summer half-year was very unusual in the pre-2012 historical record and this recovery was amongst the most abrupt on record (for any season).
The 2011/2012 groundwater drought resulted from a lower than normal winter recharge in the previous winter, 2010/2011 and from the delayed onset of the 2011/2012 recharge season with recharge for the winter half-year 2011/2012 typically below 20% of the seasonal average over wide areas of the UK.
As a result, new record March minima were reported for many observation boreholes in March 2012 (see map of March 2012 groundwater levels), and only in 1992 has the overall aquifer storage been lower than in March 2012 (Marsh et al. 2013). Over the period of the drought, the Chalk was the worst affected aquifer (Marsh et al. 2013). The end of the drought was rapid with large recoveries in groundwater levels seen in short periods of time, particularly on the Chalk (see Marsh et al. 2013), recording above average or new maxima by August. Although the relatively slowly responding groundwater levels in the Permo-Triassic Sandstone of the Midlands and north-west, such as at Heathlanes, did not return to monthly averages until April 2013 (Marsh et al. 2013).
There was a large contraction in the groundwater supported stream network and the cessation of flow in many winterbournes with the most significant effects seen towards the end of the drought period (Marsh et al. 2013). Reduction of groundwater baseflow in many rivers contributed to low flows and to the deterioration of river and wetland water quality through low oxygen levels, decreased effluent dilution and algal blooms, and the loss of habitat and fish kills due to stream network shrinkage. The first Drought Orders (colloquially known as ‘hosepipe bans’) were issued as early as June 2010 (Marsh et al. 2013), and by the end of the drought a wide range of the mitigation actions were in place, including low flow augmentation and the use of emergency groundwater sources, and by April 2012 Drought Orders affected ~20 million people.
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The ecological and environmental impacts were more focused on periods of seasonally depressed river flows and wetland water levels; these were often exacerbated by the limited dilution of effluents, low oxygen levels and the development of algal blooms – together resulting in considerable stress on aquatic wildlife. Such circumstances also led to a loss of visual amenity and decreased opportunities for recreational activities.
Following abundant replenishment, in November 2009 reservoir stocks were very healthy across almost the entire country but the water resources situation then deteriorated rapidly through the first six months of 2010, in western regions particularly. The March-June period saw the largest fall in overall reservoir stocks for England & Wales since 1995 and levels were particularly depressed in a number of smaller impoundments. In Scotland levels in Loch Katrine fell considerably below its previous June minimum in a series from 1994. By late-June, the combined stocks for a network of major reservoirs in north-west England were at their lowest for the time of year since the 1984 drought; this triggered the introduction of a temporary use ban (including a domestic hosepipe ban) affecting over six million people.
Fortunately, the exceptionally wet July ensured substantial inflow from the steep upland gathering grounds and most reservoir stocks recovered through the late summer and autumn. There were exceptions: in south-west Britain, Clatworthy registered its second lowest October level since the terminal phase of the 1995 drought. Late in 2010, the stress on water resources was locally exacerbated during the exceptionally cold December. Many reservoirs registered their largest November-December decline in stocks as frozen catchments greatly limited inflows and in Northern Ireland, there were substantial water supply problems. Modest rainfall during the winter half-year of 2010/2011 resulted in natural replenishment to a number of major lowland reservoirs in England which were only around half of the long-term average and the spring of 2011 proved pivotal to the drought’s development. Dry weather and high temperatures in March and April increased water demand and accelerated the depletion of reservoir stocks. Notably low late spring reservoir levels were widely reported; in Wales, May stocks were the lowest since the 1995 drought in the Elan Valley reservoirs. Across much of southern and central England (extending into South Yorkshire) water companies were increasingly drawing from alternative sources to help conserve reservoir stocks through the summer half-year. Nonetheless, stocks in gravity-fed reservoirs were generally well below the seasonal average by the summer; in Devon, stocks for early-July in Wimbleball reservoir equalled their lowest on record.
In most northern and western areas, stocks recovered through the late summer and autumn 2011 – by which time they were approaching, or exceeding, seasonal maxima in Scotland. In contrast, the depletion of stocks continued through the autumn of 2011 in the drought-affected regions. Late autumn stocks for Bewl reservoir were close to the lowest on record and, in the Midlands, the Charnwood group of reservoirs fell below 40% of capacity by late-October. Careful management of river abstractions and preferential drawing on groundwater sources helped maintain stocks in a number of large pumped storage reservoirs (including those servicing London’s water needs) but, in December, stocks across much of southern England were seasonally depressed.
Generally, the recovery of stocks through the winter of 2011/12 was, again, weak; reservoir levels remained close to, or below, previous late winter minima across southern England and parts of the Midlands. March then saw the largest early spring decline in overall reservoir stocks for England & Wales since 1993. Early-April stocks were the lowest on record for a number of major reservoirs, including Rutland, and stocks in a few southern impoundments (e.g. Bewl; Figure 15c) were only around 50% of capacity. Many farm reservoirs had also failed to fill through the winter and levels in a number of reservoirs servicing the canal network were also depressed. For example, reservoirs supplying the Oxford Union Canal remained below half of capacity and Naseby Reservoir, the primary feeder into the Grand Union Leicester Line, was at its lowest, for the beginning of the boating season, in a 20-year record.
In 2011, up to 85% of the UK's cereal crops were affected, with around 20% of winter wheat and barley crops severely hit. The drought suddenly ended with extreme rainfalls and flooding that caused even more problems for growers. Dry weather started to be reported in mid-March 2010. The drought triggered an early start to the irrigation season and affected cereals’ early growth.
In East Anglia, crop yield potential was already affected, with crops on sandy soils beginning to suffer drought stress and die back. The impact of the driest start to summer for decades was felt in the grain markets. Wheat yields in France and Germany were thought to be worst affected by the long, dry spell and UK yields were also expected to suffer, but to a lesser extent. Wheat yield losses to the industry averaged between 1-2t/ha, costing UK growers around £40 million, simply as a result of crops not having enough water when they needed it. After such a dry growing season in 2011, crops on clay and chalk soils appeared to be performing the best, while those on sandy soils suffered badly from drought. Up to 85% of the UK's cereal crops were affected, with around 20% of winter wheat and barley crops being severely hit.
“Farmers worried that they may not be able to supply contracted tonnage from the drought-stricken 2011 crop are urged to contact their buyers and negotiate an early solution”. 'Drought-hit farms urged to keep buyers informed', Farmers Weekly, 20 May 2011, Vol 155 (21), p27
“Most irrigators are working flat out, often just to keep pace with potatoes, onions and other high value crops. Any spare water can be applied to sugar beet or even wheat, which will pay off with increased yields”. 'Arable: Irrigating wheat and sugar beet will pay off', Farmers Guardian, 27 May 2011, p15
Grass shortages across the country in 2010, especially in the north, south and east, posed massive challenges to farmers. Livestock farmers across the country reported significant forage shortages as a result of a lack of rain, with reductions in silage yields of up to 40% compared to the previous year and hay crops down by as much as 50%. Livestock farmers faced high feed costs. In 2011, spring growth in the Midlands and the South was well down and in some places virtually non-existent, in contrast to Scotland and the North of England where plenty of rainfall led to good growth.
In May 2011, the Environment Agency stopped farmers in the West Midlands abstracting water from rivers due to low flows and so water reserves within on-farm reservoirs were going down fairly quickly. Farmers in the South East received a notice to cease their abstraction, and some voluntary restrictions were in place in the East of England. In summer 2011, farmers with winter storage reservoirs that were running very low because of the dry winter were allowed to apply for permission to top them up. In February 2012, farmers were facing restrictions on abstracting from rivers to irrigate crops, and households faced hosepipe bans. Voluntary restrictions were started again in March 2012 in some areas of the East of England. And soon after, it started raining…
The newspapers frequently mentioned that dry weather conditions affected the water levels of rivers and reservoirs and the tabloids specifically mentioned the negative impact of the drought on wildlife and plants/gardens. There were also frequent mentions of the introduction of hosepipe bans and applications for drought permits, usually related to places in England. Scotland’s water resources were also cited since Scotland could provide water to drought-hit England.
When specific areas are mentioned, the Midlands and South East England are the most cited. However, while the tabloids also reported on the drought hitting North West England, the broadsheet paid attention to Yorkshire. The newspapers frequently mentioned that dry weather conditions affected the water levels of rivers and reservoirs and the tabloids specifically mentioned the negative impact of the drought on wildlife and plants/gardens. There were also frequent mentions of the introduction of hosepipe bans and applications for drought permits, usually related to places in England. Scotland’s water resources were also cited since Scotland could provide water to drought-hit England.
Parliamentarians express concerns about the availability of water for farmers – competition for water is seen as problematic – drought becomes understood as a phenomenon shaped not just by natural forces, but also social, political and economic interests – more Parliamentary discussion now of a changing climate and the need for resilience.
In May 2011 discussions in Parliament focus on the drought’s impact on farming. Several Members of Parliament (MPs) voice the concerns of people in their constituencies regarding the water abstraction regime, which is thought to no longer serve farmers well. Afraid that water restrictions would be imposed later in the year, especially during the summer, farmers started to use their allocated abstraction amounts (set through quotas) earlier than usual in the year. MPs also voice concerns about ‘competing priorities for abstraction’ between different stakeholders: the Environment Agency, water companies, farmers and internal drainage boards. In these debates, water shortage and drought are therefore portrayed not only as natural phenomena, but also as shaped by social, political, and economic interests. The focus in these debates appears to be not on identifying the factors that may drive drought, but on how different social groups experience and deal with drought as a result of their varying access to resources, for example, different access to infrastructure such as reservoirs. The Government is considering whether to reform the water abstraction regime to facilitate investment in order to respond to the increased variability and the reduced availability of water due to a changing climate. Hence, water management and water-related risks are discussed in the context of greater environmental transformations, such as a changing climate. In June 2011 a series of measures are put in place to deal with reduced water flows in rivers. The Government also talks about long-term plans for dealing with water scarcity: building infrastructure and the need to develop further plans for building resilience in the future. Special consideration is given to the impact of water scarcity on the environment and conservation.