India, on course to become the world’s most-populous country, risks approaching the limit of human survival as it experiences more intense and frequent heat waves.

The national weather office has forecast rising temperatures in the coming weeks after India experienced its hottest February since 1901. That’s stoked concerns that there will be a repeat of last year’s record heat wave, which caused widespread crop damage and triggered hourslong blackouts.

While temperatures as high as 50 degrees Celsius are unbearable in any condition, the damage is made worse for those of India’s 1.4 billion population who are stuck in tightly packed cities and don’t have access to well-ventilated housing or air conditioning.