A study estimates a single day of extreme heat causes about 3,400 excess deaths in India, while a five-day heatwave leads to nearly 30,000. Uttar Pradesh accounted for around 8,100 deaths during a five-day heatwave, with districts like Ahmedabad, Jaipur and Surat exceeding 250 deaths in single event. 'Excess deaths' refers to deaths above expected level based on historical data.