In recent years, the UK has seen extremes of weather with four out of the last five winters being colder and drier than average. The winter of 2011/12 saw above average temperatures but was followed by the wettest April on record, and the wettest summer in 100 years. In fact, five out of the last six UK summers had above average rainfall (2010 is the exception), leading to localised flooding and disruption.
Weather extremes are severely affecting the water industry, and swings from one weather event to another can pose significant challenges for water utilities. In an industry that relies on the natural environment to satisfy customers’ demand for water and to process the subsequent sewage output, any disruption in this environment is likely to have consequences spanning across the whole business. The operational and financial performance of a water company is inextricably linked to weather conditions, which affect asset serviceability and maintenance, and long-term strategic planning and investment decisions.
Winters: The Met Office’s preliminary research suggests we are getting more rain and we are seeing a change in the nature of the rain we get, with extreme daily rainfall becoming slightly more frequent, most notably during the winter season.
Winter impacts have been particularly significant in recent years. After more than a decade of relatively mild winters prior to 2008, the winter of 2010/11 was especially severe (see graph). Significant falls in temperature over several weeks caused pipes to freeze at treatment works, increased pipe leakage and bursts – leading to massive demand on the network – and made access to assets and customers difficult. The increase in pipe bursts caused considerable operational difficulties for water companies, including fluctuations in workload and resources.
The impact was exacerbated when the subsequent thaw at the end of the cold spell led to many burst pipes and other asset failures. The large volumes of customer calls received, particularly during the Christmas and New Year holiday period, compounded pressure on staff and led to unplanned overtime. Additionally, the reduced effectiveness of biological sewage treatment posed the potential risk of missing environmental consents.
The graph shows a prolonged drop in UK minimum temperature during the winter of
2010 /11 in comparison with the long-term average (1981-2010)
Summers: A look at the weather (rainfall and temperature) experienced in recent summers highlights the different challenges the water industry faces year on year, which in turn can have a significant impact on resources.
For example, 2012 was a summer of cool temperatures and above average rainfall. Although demand for water was reduced, rainfall caused widespread river and surface water flooding, threatening treatment works and other assets. Other impacts included property flooding from overloaded sewers and a higher than average number of pollution events.
Financially, the impacts of this rainfall were significant for UK water companies with the increase in the number of houses on their DG5 register. As the summer progressed, the impacts of one in five or even one in ten year rainfall events were having an unprecedented impact on property flooding because of very high ground saturation.
Analysis by the Met Office shows that the prolonged rainfall throughout the summer produced antecedent wetness conditions, which modified the impacts of relatively frequent subsequent rainfall events to reflect impacts normally associated with much rarer rainfall amounts. This caused a significant increase in short-term recovery costs and longer-term investment in flood prevention for UK water companies.
Conversely, this summer has seen warm temperatures and below average rainfall, which has led to high daytime water demand and legitimate night use. The prolonged summer spell meant treatment works and pumps were operating at near full capacity in many regions, leading to increased energy bills and overtime expenditure. Had the summer weather continued unabated, the potential for not meeting demand may have become a reality.
This has highlighted the importance of accurate water resource and demand planning. The Met Office has carried out recent work with Thames Water to provide a demand model for the industry. This allows UK water companies to strategically analyse and project future water demand in their region. It also has a 15-day forecasting capability, helping water resource managers make short-term operational decisions to meet consumer demand in the most efficient way.
Water companies can better prepare for the impacts of weather by using weather forecast information. With winter fast approaching, water utilities should act now to militate against severe winter weather. The Met Office expects some weather extremes to increase as a result of climate change and is leading the way to help utilities understand the potential implications and how to become more resilient to these extremes.
Stephen Herndlhofer, head of data services at Yorkshire Water, says: “We need to respond with more proactive, integrated and considered mitigation plans, including systems which make more effective use of raw meteorological data.
“Our preparation for future events certainly requires a greater appreciation of how different weather events affect all aspects of the organisation, and what action we need to take to minimise both avoidable service failures and associated recovery costs.”
There is currently a large disparity in how water firms make use of weather data in the planning, reacting and recovery stages of weather impact events. Given that the industry constantly faces the impacts of severe weather, it is widely recognised that there is a need for a more proactive approach.
The aim of the Met Office is to work with the industry to provide an understanding of what to expect from the weather now, and in the future, to help water companies manage issues such as bursts, leakage, demand and turbidity, and explore how to prepare for changes in weather patterns and to act now.
Thomas Francis, scientific consultant at the Met Office
For more information, see www.metoffice.gov.uk/water or email water@metoffice.gov.uk to receive a brochure