Greater Chennai · 2016–2026 · 30 m
Where Chennai bakes, and what to do about it
Ten years of Landsat thermal imagery, a two-million-parameter neural network, and one uncomfortable finding: the two hottest places in this city are rubbish dumps, and the model found them without being told they exist.
The surface
Heat is not spread evenly, and it is not about the sea alone
Blue runs cooler than the Chennai average, red runs hotter. This is land surface temperature — the ground, roofs and roads, not the air — at about half past ten in the morning on clear days in March to June, averaged across 66 satellite passes.
Ward outlines and the road network are drawn from OpenStreetMap. Grey means no valid land pixel — sea, river, or cloud in every scene.
Where it concentrates
A ward average is the wrong unit
Ward 189 sits at −1.51 °C and ranks 190th out of 198 — one of the coolest places in Chennai. It also contains nine-tenths of a square kilometre burning at +7.01 °C. Pallikaranai marsh cools the average while a dumping ground burns inside it.
Twelve wards hide a patch more than 4 °C above their own mean. Anyone allocating a budget by ward average would rank both of Chennai's landfills near the bottom of the list.
The finding
The model located both dumping grounds by itself
It was trained to predict surface temperature. Nobody gave it a map of waste sites. The two largest patches it flags fall inside the OpenStreetMap landfill polygons for Pallikaranai Dumpyard and Kodungaiyur Corporation Landfill — the hot cores covering roughly 80–87% of each site's footprint.
These are not ordinary hot surfaces. A landfill is thermogenic: anaerobic decomposition liberates heat from inside the waste mass, so it is an active heat source day and night rather than a dark surface warmed by the sun.
How much hotter each site runs than the built-up land around it
What to do
The ranking flips depending on what you are trying to fix
Cool pavement is near the top if you are minimising what a satellite sees. It is actively harmful if you are minimising what a person feels: a measured +3.2 °C on mean radiant temperature for someone standing on it, while air temperature fell about half a degree. In 80% humidity a body has no evaporative headroom to absorb that extra radiant load, so it is worse here than in the dry US cities where it was measured.
So there is no single ranking. Pick what you are optimising:
Humidity does not penalise everything equally
Shade blocks radiation, which humidity cannot interfere with — which is why India still records up to −5.6 °C at pedestrian level under street trees. Evapotranspiration needs dry air to work, and Chennai does not have any: a tropical green roof delivers −31% of daily roof heat flux and −0.4% at the peak hour. A flat "green is good" assumption ranks these two families exactly wrong.
Things that make it worse
Your area
Look up a place
Fifty neighbourhoods, each measured over a one-kilometre circle: how hot it runs, what it is made of, why that makes it hot, and what the evidence supports doing there.
Limits
What this cannot tell you
Every intervention figure on this page traces to a named, published study; where no study exists, the page says so instead of estimating. Costs are deliberately not shown —