A measure of how hot or cold the air is, reported in Celsius across South Asia — the single number that decides whether a pre-monsoon afternoon is merely hot or genuinely dangerous.
BasicsWhat is Temperature?
Temperature is a measure of the average kinetic energy of the molecules in the air — in plain terms, how hot or cold the air is. It is the most fundamental variable in meteorology, the one every other quantity is read against: humidity is meaningful only relative to temperature, pressure systems are born from temperature contrasts, and the monsoon itself exists because land heats faster than the ocean.
Across India, Pakistan, Bangladesh, Nepal and Sri Lanka, temperature is reported in degrees Celsius, the scale where the freezing point of pure water at sea level is 0 °C and its boiling point is 100 °C. Fahrenheit survives mainly in older habit and in some imported appliances; the conversion is °F = °C × 9/5 + 32, so 40 °C is 104 °F. Scientists also use the Kelvin scale, which starts at absolute zero, −273.15 °C, the point at which molecular motion effectively stops.
In this region the number carries unusual weight. A forecast max of 38 °C and one of 45 °C are not two shades of the same summer day — one is uncomfortable, the other shuts down outdoor labour and fills hospital wards.
How temperature is measured
A weather-station temperature is not simply a thermometer left outside. To be comparable between Karachi and Kolkata, it has to be measured under standard conditions:
- Inside a white louvred screen — the Stevenson screen, or a modern ventilated radiation shield — which blocks direct sun and reflected heat while letting air flow freely across the sensor.
- Mounted between roughly 1.25 and 2 metres above the ground, commonly 1.5 m, over short grass rather than concrete or tarmac.
- Away from buildings, walls and paved surfaces that radiate stored heat.
That is why an official reading can be several degrees lower than the number on a car dashboard or a phone left on a scooter seat. Those surfaces are measuring their own heated material, not the air.
Stations report a maximum and a minimum for each day, once from mercury and alcohol thermometers and now from electronic sensors logging continuously, while radiosondes on balloons measure the temperature profile aloft. Higher up, temperature normally falls with height at an average of about 6.5 °C per kilometre — the reason Shimla and Gangtok stay cool while the plains below them bake.
Temperature across South Asia
Few regions on Earth pack a wider temperature range into so short a distance.
- The pre-monsoon furnace (March to June). Heat builds over the northern plains, western Rajasthan, Sindh and southern Punjab until the monsoon breaks it. India’s highest reliably recorded temperature, 51 °C, was measured at Phalodi in Rajasthan in May 2016. Jacobabad in Sindh and Turbat in Balochistan are routinely listed among the hottest inhabited places anywhere.
- Monsoon relief, then humidity. Once the rains arrive, daytime maxima across most of the subcontinent fall sharply — but minima stay high and humidity climbs, so nights become oppressive even as the afternoons cool.
- October heat. After the monsoon withdraws, central and peninsular India often see a second warm spell with clear skies and still-high humidity before winter sets in.
- Winter. The Indo-Gangetic plain can approach freezing on cold-wave nights, with Punjab, Haryana, Uttar Pradesh and Bihar worst affected. Kashmir, Himachal Pradesh, Uttarakhand, Nepal and Gilgit-Baltistan fall well below zero, while Kerala, Tamil Nadu and coastal Sri Lanka barely register a cold season at all.
- Coasts versus interiors. Mumbai, Chennai, Karachi and coastal Bangladesh have a small diurnal range: the sea moderates both ends, so days are less extreme but nights stay warm. Desert and plateau stations swing far more widely, because dry air and clear skies let heat escape rapidly after sunset.
- Cities versus countryside. Built-up areas hold heat overnight through the urban heat island effect, so a city-centre minimum can be noticeably higher than one recorded at an airport observatory on the outskirts.
Why the temperature alone does not tell you how it feels
A dry 44 °C afternoon in Bikaner and a humid 34 °C afternoon in Kolkata can carry similar physiological risk, because the body cools itself by evaporating sweat and humid air blocks that mechanism. This is the single most important thing to understand about temperature in South Asia.
Forecasts therefore publish feels-like values that combine temperature with humidity and wind. The heat index is the familiar summer version; wind chill is its winter counterpart in the hills. For the most severe humid-heat episodes, meteorologists watch the wet-bulb temperature, the most direct indicator of whether the body can shed heat at all — and the coastal belts of Sindh, Gujarat and the Bengal delta are among the regions most closely studied for it.
The India Meteorological Department declares a heatwave using both absolute thresholds — broadly 40 °C in the plains and 30 °C in the hills — and the departure from that station’s normal, so an unusual 38 °C in a normally mild location can qualify while a routine 42 °C in the desert may not.
Temperature, health and the working day
Heat risk falls hardest on people who cannot avoid it: construction workers, farm labour, street vendors, rickshaw and delivery riders, and anyone living in a tin-roofed room. Several Indian cities now run heat action plans that shift working hours away from the afternoon, open cooling centres and issue advance warnings — the response to repeated severe heat events, including the widely reported 2015 heatwave across Andhra Pradesh, Telangana and Sindh.
Cold does damage too, and is often underestimated. North Indian and Pakistani cold waves are dangerous chiefly to people sleeping outdoors and to the elderly, and they coincide with the worst fog and air-quality episodes of the year.
Temperature also sets the agricultural calendar. Wheat in the northern plains is sensitive to warm spells during grain filling in February and March; a sudden hot week at the wrong moment reduces yields regardless of how good the winter was.
Frequently asked questions
Why does the official temperature feel lower than what my phone shows outside? Official readings are taken in shade, in a ventilated screen, about 1.5 m above grass. Direct sun, concrete, tarmac and vehicle bodywork all read much hotter because they measure heated surfaces rather than the air.
What is the difference between temperature and feels-like temperature? Temperature is a physical measurement of the air. Feels-like combines it with humidity and wind to estimate the strain on your body. In humid coastal cities the feels-like value is often far higher than the thermometer reading.
Why are nights so much hotter in cities? Concrete, asphalt and brick absorb heat all day and release it slowly after sunset, while buildings block the sky view that lets heat radiate away. This urban heat island effect keeps city minima elevated, which matters because the body needs a cool night to recover from a hot day.
Why is it colder in the hills even though they are closer to the sun? Distance to the sun is irrelevant at these scales. Air cools as it rises and expands, and on average temperature falls by roughly 6.5 °C for every kilometre of altitude, so a hill station a kilometre and a half above the plains sits about ten degrees cooler.
Where can I check the temperature for my city? Mausam Online publishes hourly temperature, the daily maximum and minimum and the feels-like value for every city it covers, including Delhi, Mumbai, Jaipur, Lahore, Dhaka and Srinagar.