Life comes to a standstill in summer. Temperatures in parts of north and central India have already crossed 44°C in May 2026. Our country is now reeling under a severe heat wave, which has had a significant impact on food grain productivity. Due to the intense heat wave, farmers are unable to work long hours in the fields, and there is a lack of adequate irrigation water. These two problems are threatening the supply of crops today.
DEFINING THE THREAT
A heat wave is a prolonged period when the maximum temperature at a place rises significantly above its long�term average, typically calculated over the past three decades. In practice, if the temperature stays about 4.5 to 6.4°C above normal for three to five consecutive days or crosses 40°C in the plains, 37°C in coastal areas, or 30°C in the hills, it is generally classified as a heat wave. The India Meteorological Department (IMD) often uses a slightly lower threshold of around 4.5 to 6.4°C above normal for two days, while the World Meteorologic al Organization (WMO) considers five or more days of unusually high temperatures a heat wave episode.
Normally, the human body temperature is about 37°C. When ambient temperature approaches or exceeds that level, the body can no longer shed heat by simple conduction or convection, so it must rely increasingly on sweat evaporation. Sweating cools the body because evaporation removes heat, but the effectiveness of this mechanism falls sharply when humidity is high. Moist air slows evaporation, meaning the same amount of sweat produces less cooling and more dehydration. As a result, during intense heat waves, especially in humid conditions, vulnerable groups face much higher risks of heat exhaustion and heatstroke. Humidity effectively raises the “feels-like” temperature, turning heat waves into a silent killer. To track these hazardous conditions, the Meteorological Department introduced a heat index: When the index exceeds 40°C, heatstroke risk rises rapidly. A recent report found that gig workers in Delhi are experiencing a recovery deficit, starting each day already physically drained because warm nights prevent proper recuperation.
THE MECHANICS OF A “FLASH DROUGHT”
Global warming has brought frequent heat waves to nearly every major Indian metro city. This is further intensified by the urban heat-island effect, which acts as a localized multiplier. Concrete and asphalt absorb heat during the day and release it at night, while densely packed skyscrapers block proper ventilation and air conditioners pump out massive waste heat. Alarmingly, this warming has extended to rural villages. Environmentalists warn that even if we completely stop carbon emissions right now, global temperatures will still increase by 2°C due to atmospheric lag. Continued emissions at the current rate could cause an average spike of 7°C by the end of this century. When heat persists, water is lost rapidly from soil and plants through evapotranspiration, which is the combined total of direct soil evaporation and plant transpiration via leaf stomata. When accelerated evapotranspiration pairs with a significant rainfall deficit, soil moisture decreases within a few weeks, triggering what scientists call a flash drought. This sudden onset destroys crops during highly sensitive growth stages like flowering and pollination, decimating yield, quality, and market prices.
THE GROUNDWATER CRISIS
To fight water scarcity, farmers turn heavily to groundwater. However, a study in Science Advances warns that India’s groundwater depletion rates could triple by midcentury due to climate warming. Higher temperatures reduce natural aquifer recharge because moisture evaporates before sinking into the ground. At just 1°C of global warming, deep-water aquifers could drop by 36 cm annually between 2041 and 2080. Because deep aquifers take far longer to refill, today’s intensive irrigation guarantees a permanent water crisis tomorrow. Ultimately, heat waves are a systemic crisis intersecting water, soil, labor, and food security. Without rapid heat-warning networks, heat-tolerant seeds, and moisture conservation, the future of Indian agriculture remains deeply precarious.
(THE WRITER IS A SCIENCE WRITER AND RESEARCHER)