NEW DELHI: Electricity supply across India will be vulnerable to disruptions this summer as the official forecast of severe heatwave will boost demand significantly, while power stations face acute water shortage this year because of the alarming dip in water levels that has forced some plants to shut down.Water shortage is not only hurting coal-based and hydropower plants but will also decrease the efficiency of solar and wind plants, adding to the pressure on the grid. Coal-based power plants need water for cooling and ash disposal.Temperatures have already been more than 5 degrees above normal in recent weeks, and the trend is likely to continue in the peak summer months, according to the firstever temperature forecast issued last week by the India Meteorological Department . This has already boosted demand, which is expected to soar to record levels as the summer intensifies, industry executives and analysts said.PwC leader Kameswara Rao said generation capacity or distribution companies’ ability to pay may not matter much this summer as there is surplus generation capacity available at low prices. “Instead, water availability and grid reliability hold the key,” he said.“Water shortage can stall operations of coal-based power plants, and a decision to shut down older, smaller unit-sized plants that overuse water may become necessary.State generation companies are at most risk and have to undertake water audits and invest in conservation,” he said. Feedback Infra chairman Vinayak Chatterjee said hotter than usual summer will affect water availability, generation from coal and hydropower plants and spur transmission and distribution outages.Water shortage has already led to closure of some power plants in Karnataka, Madhya Pradesh , Bihar and West Bengal, including NTPC ’s Farakka unit. Rao said renewable energy companies are affected too. Over fourfifth of large hydro reservoirs hold lower water levels than previous year. Power generation from hydel plants was about 15% less in 2015-16 than the previous year.High ambient temperature impairs solar generation, and wind farms have already suffered the impact of El Nino effect. Steep demand from air-conditioning and water pumping in urban areas could overload the grid causing outages, Rao added.Water situation in parts of the country has worsened after an extended period of deficit rainfall, including two consecutive monsoon failures. Water levels in the country’s 91major dams have plunged to 25% of their capacity and well short of the 10-year average, possibly impairing electricity production, especially in the southern and western states.“The rise in temperature in April will result in higher demand for power,” said Sonu Agrawal, managing director, Weather Risk Management Services. Agrawal said power demand this month may see a 3-5% year-on-year rise in north, north west and central Indian cities like Delhi, Jaipur, Indore and Ahmedabad.Agrawal said average maximum temperature for April showed a rise of about 4-6 degree Celsius in north, north west and central parts of the country.Meteorologist and power distribution companies say a variation of 1 degree Celsius temperature from normal can lead to increase in demand of power by 300-350 mw in Delhi alone to beat the heat. This will benefit idle power generation capacity. BSES Rajdhani Power vice-president Satinder Singh Sodhi said day demand in peak hours in Delhi touched 3,700 mw on Saturday, compared to normal demand of 3,300-3,400 mw.