India and Pakistan are no strangers to heat. This time of year is the worst, as heat peaks before the monsoon brings cooler conditions from June.

But this year’s heat is something else. Intense, sustained heat began in mid-April. Daily maximum temperatures have topped 46°C in many locations, with some areas running around 5–8°C above seasonal norms.

The unrelenting heat has driven record demand for electricity in India as people turn on air conditioners – and worsened drought conditions affecting more than a million square kilometres across both countries.

When extreme heat combines with humidity, it can be lethal. Human bodies cannot cool themselves easily in these conditions. The heatwave has claimed at least 37 lives in India and 10 in Pakistan. These figures are likely to be a major underestimate, as heat-related deaths are systemically undercounted in India.

It’s usually a hot wait for the monsoon. But several factors can line up to make a bad season much worse.

One reason it’s been so bad this year is due to persistent high-pressure weather systems. When these systems sit in place, they make heatwaves more likely by suppressing cloud formation and reducing the chance of cooling rain. This year, strong high-pressure systems have lingered over parts of India and Pakistan, trapping hot air near the surface and allowing temperatures to build over many days.

With less rain, there’s more heat at ground level and soils dry out. Drier soils make things........

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