The forecast looked similar in most of neighboring Pakistan, where government forecasters said this week that a high pressure system would likely keep temperatures above normal through Monday.

Pakistan’s Meteorological Department also warned that in regions dotted with glaciers, the heat could lead to so-called outburst floods, in which water spills from glacial lakes into populated areas. In 2013, an outburst flood in the northern Indian state of Uttarakhand led to flooding that destroyed villages and killed several thousand people.

In both countries, the forecasts cited only temperature, not the heat index — a measure that combines temperature and humidity and tends to give a more accurate portrait of what extreme weather feels like.

Fusaram Bishnoi, a doctor in Barmer, an area of Rajasthan that has recorded some of India’s highest temperatures this week, said he had seen a surge of patients arriving with heat-related illnesses in recent days. That includes not only heat stroke, he said, but also food-borne illnesses linked to the consumption of food that spoiled in the heat.

“We tell people not to venture out during the day and to drink more, and more water,” Dr. Bishnoi said.

The extreme heat poses a problem for agriculture, a primary source of income for hundreds of millions of people across the subcontinent. In India, wheat farmers have been saying for weeks that high temperatures were damaging their yields. The Indira Gandhi Memorial Tulip garden closed a week early this spring because many bulbs had flowered and then died before an annual monthlong exhibition had run its course.

Mr. Bose, the farmer, who lives in the Barmer district of Rajasthan, said that about 15 to 20 percent of the local wheat crop, as well as half the cumin crop, had already been lost because of unseasonably hot weather and changes in wind flow. It does not help, he added, that the current heat wave has made it harder to work outdoors.

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