Heat index risk categories (NWS)
The National Weather Service heat index scale translates combined heat and humidity into health risk levels. This calculator adds activity, age, and hydration modifiers to give a more personalised risk estimate.
| Heat index | Category | Risk |
|---|---|---|
| Below 27°C / 80°F | Safe | No significant heat stress |
| 27–32°C / 80–91°F | Caution | Fatigue possible |
| 33–39°C / 91–103°F | Extreme Caution | Heat cramps / exhaustion possible |
| 40–51°C / 103–124°F | Danger | Heat exhaustion / heatstroke likely |
| Above 51°C / 125°F | Extreme Danger | Heatstroke imminent — emergency |
Base categories from NWS. Calculator adds activity (+4 to +15°F), age (child/elderly +5°F), and dehydration (+7°F) modifiers.
Pakistan's heatstroke crisis
Pakistan is one of the countries most severely affected by heat waves. Temperatures in interior Sindh, Southern Punjab, and Balochistan regularly exceed 45°C in May and June. Jacobabad — often cited as one of the hottest cities on earth — has recorded temperatures above 50°C.
The deadliest recent event was the 2015 Karachi heat wave, which killed an estimated 1,200–2,000 people in five days. The disaster was worsened by simultaneous power outages that left residents without fans or air conditioning, combined with high humidity from monsoon winds, and limited public cooling centres.
Climate change is making Pakistan's summers hotter and longer. A 2022 study in Nature Climate Change found that parts of the Indus Valley may experience wet-bulb temperatures that exceed human survivability thresholds by mid-century without significant emissions reductions.
Emergency: recognising and treating heatstroke
Call for help immediately if someone has: a body temperature above 40°C, confusion or slurred speech, hot/red/dry or damp skin, rapid strong pulse, nausea or loss of consciousness.
While waiting for emergency services: move them to a cool, shaded area; remove excess clothing; apply cool water to the skin and fan them vigorously; apply ice packs to neck, armpits, and groin; do not give fluids to an unconscious person.
Do not assume they will recover on their own — heatstroke can cause permanent brain, kidney, and heart damage within minutes of onset. Every minute of untreated hyperthermia matters.
Frequently asked questions
What is the heat index?
The heat index (also called 'feels like' temperature) combines air temperature and relative humidity to estimate how hot it actually feels to the human body. High humidity reduces the evaporation of sweat — the body's primary cooling mechanism — making the same temperature feel much hotter and significantly raising heatstroke risk.
What is heatstroke and how is it different from heat exhaustion?
Heat exhaustion: heavy sweating, cool pale skin, weakness, nausea, headache. Usually resolves with rest, shade, and fluids. Heatstroke: body temperature above 40°C, confusion, hot/red/dry skin, rapid pulse, loss of consciousness. Heatstroke is life-threatening and requires emergency medical care immediately.
Why is Karachi so dangerous in a heat wave despite being coastal?
Karachi's coastal location brings high humidity, which prevents sweat from evaporating effectively. During heat waves, this combination of heat and humidity creates extremely high heat index values. The 2015 Karachi heat wave — which killed over 1,200 people in five days — was driven by this exact combination, made worse by power outages that disabled fans and air conditioners.
Who is most at risk from heatstroke in Pakistan?
The highest-risk groups are: outdoor labourers (construction workers, farmers, rickshaw drivers), the elderly, young children, people with heart disease, diabetes, or kidney disease, people taking diuretics or beta-blockers, and those without access to air conditioning. Low-income communities in dense urban areas are disproportionately affected.
What is the emergency treatment for heatstroke?
Call emergency services immediately. While waiting: move the person to a cool, shaded area; remove excess clothing; apply cold water or ice packs to the neck, armpits, and groin; fan them vigorously; do not give fluids to an unconscious person. Do not delay cooling — every minute of elevated body temperature increases organ damage risk.
How much water should I drink in extreme heat?
In extreme heat (heat index > 40°C), adults should drink at least 500–750 ml of water or ORS per hour during outdoor activity — much more than the standard daily recommendation. Do not rely on thirst as a guide in heat; by the time you feel thirsty, mild dehydration has already begun. ORS sachets help replace sodium and potassium lost in sweat.
Can I prevent heatstroke while fasting in Ramadan?
Ramadan heat risk is real — especially for outdoor workers fasting during summer months. Maximise hydration between Iftar and Suhoor. During the fast, avoid peak sun hours (11am–4pm), wear loose light-coloured clothing, rest in shade or cool indoor spaces, and watch for warning signs. The Ramadan Medication Planner on PakVita addresses timing of medications for conditions like heart disease that increase heat sensitivity.
What should I wear to stay cool in Pakistani summer heat?
Loose, light-coloured, breathable natural fabrics — cotton or linen — are most effective. Light colours reflect sunlight; dark colours absorb it. Cover the head with a damp cloth or cap when outdoors. Avoid synthetic fabrics that trap heat. Women's traditional shalwar kameez in cotton is well-suited to heat management.