The max-temperature charts shrug. Your body doesn't. If you looked up the numbers and came away confused — you were right to be. The thermometer on a weather station pole is measuring one thing. The city around you is a different story.
Every April, the same argument: "It's worse this year." Someone pulls out a chart of peak temperatures. The chart disagrees. Both sides walk away unconvinced.
An average April day in the 1980s had 3½ hours below 22°C — the body's real recovery window. In April 2026 so far, it's under one. The heat-stress band grows by two hours. Not a warmer peak. A longer stay.
Each row is one average April day, stacked by temperature band. Dark blue is the body's recovery window. Deep red is heat stress. Watch which one vanishes and which one extends.
The decade-scale average barely budged. April 2026 is running about 1.5°C above both five-year windows — at every hour of the day. ERA5's 9 km grid averages city and surroundings, so this is a conservative picture of what the thermometer on your balcony is doing.
Source. ECMWF ERA5 reanalysis, ~9 km grid, pulled from Open-Meteo's archive API for the Bangalore coordinate (12.97°N, 77.59°E), Asia/Kolkata timezone. Three windows: April 1985–89, April 2021–25, and April 1–20, 2026.
Why five-year windows. A single April can be a freak — monsoon timing, El Niño, local weather. Averaging five Aprils smooths that out and leaves a climate-scale comparison. Each five-year line is 150 days of hourly data; 2026 so far is 20.
Why April. The pre-monsoon peak. The month Bangaloreans complain about, and the one where urban heat island effects hit hardest — dry air, high solar load, no relief from rain yet.
The metrics. Hours ≥ 26°C uses a common body-stress threshold. Hours ≥ 28°C is the sleep-quality threshold. Degree-hours above 26°C is the sum of (temp − 26) across the 24 hours of a day when that sum is positive — essentially the area under the curve above the comfort line. It's a single number for total daily heat burden.
What this is not. Reanalysis blends station, satellite, and aircraft observations into a gridded model. It's excellent for decade-scale comparison at a location. It is not the thermometer on your balcony — the 9 km grid cell averages concrete and farmland together, so it understates the urban heat island. The real city is hotter than this chart; the direction of change is the point.
A 1°C shift in the mean sounds like nothing. Bodies don't feel a mean — they feel duration. Same 24-hour day; very different number of hours spent above the lines that matter.
How many hours above each threshold · per average April day
How many hours above each sleep threshold · per average April night (22:00–07:00)
Bars to scale: pale orange is 1985–89, deep red is 2026. Same scale across each group. Day thresholds each gained 2–2½ extra hours. The night's cruelest move is at 22°C — the body's real sleep-cool window shrinks from three and a half hours to forty-eight minutes.
Three five-year windows can hide a one-off spike. So here's every April, 1985 to 2026 — forty-two years of hourly data, one dot per year, on the two metrics that matter: hours the night stayed cool enough to sleep in, and hours the day spent above heat-stress.
Each dot is one April. The line is a five-year rolling average — smooths out El Niño / La Niña flukes. 1997 was freakishly cool (look at the blue spike); 1998 came right after and flipped to brutal. Since roughly 2010 the night's recovery window has started drifting down, and the hottest Aprils have clustered: 2016, 2019, 2024, 2026. 2026 is not an outlier. It's the pattern continuing.
Hours are abstract. Clock times aren't. Here's the day — and the night — as an average Bangalorean's body used to experience it, and as it does now. The cool windows have different ends now. One of them has no end at all.
Colored zones: when the average hour sits in each state. Blue = below 22°C (real cool). Red = at or above 32°C (heat stress). Cream between.
The blue band has disappeared. The red band has moved outward at both ends but grown more at the PM end — heat stress now lasts nearly two hours longer into the evening. Clock-times measured by linear-interpolating the hourly mean curve across each crossing.
The city isn't warmer because the planet is warmer. It's also warmer because of what we paved, cut, and filled. Between 1973 and 2023, in Bengaluru:
The cheapest urban-cooling intervention ever measured. A dark concrete roof absorbs sunlight all day and dumps the heat back into your bedroom at night. A white-coated roof throws 70% of it back at the sky. Same building, different day.
Numbers from LBNL / Berkeley Lab cool-roof research and the Ahmedabad Heat Action Plan — which painted 20,000+ slum roofs white between 2017 and 2020 and measured indoor temperatures drop 2–5 °C during heatwaves.
The forest the city lost is gone. You can't replant 88% of canopy this decade. But the roofs — those are still there. Four hundred square kilometres of flat concrete, heating all day and radiating all night. All of it paintable.
Your building's terrace. Your school's. The bus stop's.
The cheapest cooling Bangalore has ever had access to.
The thermometer at the airport reads 37°C today, same as it did a decade ago. The chart looks boring. But the experience of living in Bangalore in April has changed — and not by a rounding error.
Nights don't cool off. Summer starts in March. The heat reaches you at 8:30 am. The trees that used to be overhead aren't. The lake that used to breathe onto your neighbourhood is a drainage canal. The wall facing your window has been absorbing sun since 11am and will radiate it into your bedroom at 1am.
What to watch instead of the max: the minimum overnight temperature, the number of consecutive days above 35°C, and the percentage of the day your tile floor is warmer than your body. Those are the numbers that match what you're feeling.
The city has quietly become a different climate. The charts just haven't caught up.