In April 2025, temperatures in parts of Sindh were forecast to climb past 46 degrees Celsius, well above the seasonal norm. For interior Sindh and southern Punjab, this was not just a hot spell but an officially recognised heatwave, a distinction that changes how authorities respond.

Simple Explanation

A heatwave is an extended period of exceptionally hot weather that significantly exceeds the usual historical average for a specific region. It is not simply a hot day but a prolonged event, often lasting five days or more, and frequently accompanied by high humidity that makes the heat feel more intense.

How It Works

Definitions vary by region

There is no single global temperature threshold for a heatwave. A temperature of 40°C is unremarkable in southern Pakistan during summer, but would be a severe anomaly in northern Europe.

The Pakistan Meteorological Department criteria

The Pakistan Meteorological Department (PMD) generally defines a heatwave as when the maximum temperature stays five to seven degrees Celsius above the long-term average for a specific area for more than five consecutive days.

Heat domes

Heatwaves often form when a high-pressure system traps hot air over a region, blocking rain and wind and allowing temperatures to climb day after day.

Why nighttime heat matters

If nighttime temperatures do not drop enough, the human body cannot recover from daytime heat stress, which sharply increases health risks even when daytime peaks are not record-breaking.

Why It Matters in Pakistan

Pakistan regularly experiences dangerous pre-monsoon heatwaves between April and June. In mid-April 2025, a high-pressure system pushed temperatures six to eight degrees above normal across parts of Sindh and South Punjab, with districts including Dadu, Larkana and Jacobabad forecast to exceed 46 to 48°C. Provincial Disaster Management Authorities issue alerts for these events, and outdoor labourers and residents of dense, low-income urban areas, including millions living below the poverty line in Karachi, face the greatest risk because they have limited access to cooling.

Common Misunderstandings

A common misunderstanding is that a heatwave is simply any day over 40°C. In fact, it requires temperatures to be significantly above the historical average for that specific location, sustained over several days.

A common misunderstanding is that only the daytime high matters. High nighttime temperatures are often more dangerous because they prevent the body from resting and cooling down.

A common misunderstanding is that drinking cold water alone prevents heatstroke. Hydration helps, but cooling the skin and moving to shade or air conditioning is necessary once core body temperature rises to dangerous levels.

What This Means for People

When PMD issues a heatwave warning, it is a signal to shift outdoor labour and farm work to early morning hours, check on elderly relatives and infants, and avoid unnecessary exposure during the afternoon. Employers of outdoor workers should adjust schedules during these alerts rather than waiting for visible signs of heat illness.

Conclusion

A heatwave is a sustained departure from the normal climate of a place, not a single hot afternoon. Recognising the difference, and paying close attention to nighttime temperatures, is central to staying safe as these events become more frequent.

In Simple Terms

A heatwave is a period of several days where temperatures are far above the normal average for a region, often made more dangerous by high nighttime temperatures.