Accurate weather forecasting can help water companies predict demand and allocate the proper resources to resource management and leakage, says Tom Francis.

Weather conditions have a significant effect on the operational and financial performance of a water company. With climate change predicted to increase the likelihood of extremes of weather (hotter, drier summers and milder, wetter winters) this, coupled with forecasted increases in the UK population, could present considerable supply-demand challenges to water utilities.

The weather experienced in the UK over the past two summers highlights the different environmental conditions the water industry faces each year, which has a significant impact on water availability and consumer demand.

Last summer saw warm temperatures with below average rainfall, which led to higher than average water demand, leading to more intense water treatment, more frequent pumping and higher energy bills. However, 2012 was a summer of cool temperatures and above average rainfall. The impact on the water industry was low water demand and flooding. As well as river and surface water flooding, the number of pollution events – where combined sewer overflows spilled directly into watercourses – also increased, as did internal and external property flooding where sewers were overwhelmed.

Unexpected or sudden spells of warm weather also significantly affect the industry. The heatwave in July 2013 saw high pressure sitting over the UK, which resulted in the longest spell of hot weather to affect the whole of the country since July 2006. This led to dramatic increases in night-time use of water. Households used sprinklers and hosepipes to water the garden or fill up swimming pools, while in the commercial sector golf courses, watering greens and arable farmers irrigating their land throughout the night had an impact too.

Although this extra usage was small in relation to the additional daytime demand, quantifying and separating weather-related night use from legitimate leakage (normally derived from minimum night-time measurements), particularly during autumn, enables companies to confidently plan leakage detection and repair activities through the summer and then winter to meet spring leakage targets.

The Met Office collaborated with Thames Water to deliver a model of seasonal night use to provide this critical information. It combines historic weather and company information to generate estimates of past seasonal night usage for model calibration. Linking the model to a data feed for current weather, leakage planners use the model’s output to track night use week by week in order to confidently estimate the true leakage level through the summer. This allows them to target detection resources effectively and ensure leakage targets can still be met given the severest winter weather planning scenarios.

With London’s minimum night-time use rising by almost 100Ml/d during July (equivalent to an increase of 15 per cent in leakage), some at Thames Water were concerned about the impact of the dry weather on their pipes. However, the night use model indicated this was exactly the increase expected with the onset of hot weather being followed by the start of Ramadan on 10 July, a non-weather related night-time water use increase that can often confound night use models.

Thames Water leakage planning manager Andrew Oakes says: “We used to be more or less flying blind for much of the summer, just hoping we would find leakage was OK when the hot weather ended. But now we’re happy we know how things are going, even at times of particularly hot weather.”

Weather forecast information combined with water industry specific impact forecasts are now available that can help water companies better prepare for the impacts of weather. At the Met Office, we are working with the industry to provide a better understanding of what to expect from the weather now and in the future, to help water companies manage specific issues such as leakage and demand, as well as preparing for changes in weather patterns as a result of climate change.

Tom Francis, utilities scientific consultant, the Met Office

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