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24 | 4th - 10th July 2014 | utIlIty WEEK Operations & Assets Market view W eather conditions have a signifi- cant 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 pre- sent considerable supply-demand challenges to water utilities. The weather experienced in the UK over the past two summers highlights the dif- ferent environmental conditions the water industry faces each year, which has a signifi- cant impact on water availability and con- sumer demand. Last summer saw warm temperatures with below average rainfall, which led to higher than average water demand, lead- ing to more intense water treatment, more frequent pumping and higher energy bills. However, 2012 was a summer of cool tem- peratures 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 pol- lution events – where combined sewer overflows spilled directly into watercourses – also increased, as did internal and exter- nal property flooding where sewers were overwhelmed. Unexpected or sudden spells of warm weather also significantly affect the indus- try. The heatwave in July 2013 saw high pres- sure 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 hose- pipes to water the garden or fill up swim- ming 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 measure- ments), particularly during autumn, enables companies to confidently plan leakage detec- tion and repair activities through the sum- mer 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 leak- age 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 (equiva- lent 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 oen 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 compa- nies 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 consult- ant, the Met Office It all depends on the weather Accurate weather forecasting can help water companies predict demand and allocate the proper resources to resource management and leakage, says Tom Francis. United Utilities and the Met Office The Environment Agency's guidelines on water resources management planning require water companies to provide a reliable demand forecast. United Utilities, one of the UK's largest water companies, asked the Met Office to help model the relationship between water demand and weather for its entire North West region, which comprises four disparate zones. The challenge was to show that it is possible to explain the weather-related com- ponents of demand on the basis of weather for both the region and its constituent zones. Long-term forecasts of demand, which take account of weather variability, should lead to better management of demand, better capacity planning and more accurate revenue predic- tions, thereby helping Ofwat to set accurate price limits for water utilities. Using the Met Office's Demand Weather Intelligence Model, developed in conjunction with Thames Water, it was possible to explain how demand is sensitive to weather condi- tions. The model was configured for the United Utilities region and four smaller resource zones to establish a correlation between historic weather data held by the Met Office (such as changes in air temperature and amount of rainfall) and data for water demand supplied by United Utilities. The model takes into account weather-related leakage, domestic and non-domestic usage, and other non-weather related impacts on demand such as long-term population changes and increased water metering. When suitably adjusted, the model makes it pos- sible to assess the average and dry-year demand for the coming 25 years, taking account of the range of possible weather conditions. The Met Office was able to show that weather-related demand could be modelled and therefore that reliable demand assessments could be made on the basis of weather data.