Cities Are Budgeting for Heat. Most of Them Still Measure It Wrong.

Heat has finally become a budget line. Cities that had no adaptation plan five years ago now have heat officers, cooling centre networks, and capital programmes for shade and reflective surfaces. The planning is real and mostly sensible. The measurement underneath it is not.

Most municipal heat policy is triggered by readings from a small number of official weather stations, and those stations are frequently sited in exactly the conditions least representative of where people live.

The siting problem

Official meteorological stations are placed for consistency and aviation, which means open ground, good airflow, grass surfaces, and often an airport. Those are reasonable choices for a climate record. They are poor proxies for a dense neighbourhood of asphalt, low albedo roofing, and no canopy.

Mobile and distributed sensing campaigns consistently find large intra-city differences that a single station cannot see.

• Within-city spreads of several degrees between the hottest and coolest neighbourhoods at the same hour are routine, and the spread is larger at night than at midday.
• Night-time minima are where the divergence matters most physiologically, because inability to cool overnight drives mortality more than peak afternoon temperature.
• The gradient correlates with income and canopy cover, which means a city-wide average conceals a distribution with a predictable social pattern.

Our threshold was met four times last summer according to the airport. Our own sensors in three neighbourhoods crossed the same threshold nineteen times.

Why the wrong metric produces the wrong programme

If a heat emergency is declared based on a reading that understates conditions in the worst-affected areas, three things follow mechanically.

Cooling centres open late and close early, because activation is tied to the threshold. Outreach to vulnerable residents is triggered on the same signal, so it also arrives late. And retrospective evaluation of the programme uses the same understated series, which makes interventions look more adequate than they were.

There is a fourth, subtler effect. Capital allocation for shade, canopy, and roof programmes is often prioritised using modelled heat exposure calibrated against the official station. Neighbourhoods whose actual exposure is highest can therefore be systematically underweighted in the investment that would help most.

What better measurement looks like

The technically correct answer is to measure what the body experiences rather than air temperature alone. Heat stress depends on humidity, radiant load, and air movement, which is why wet-bulb globe temperature and similar composite indices exist.

The practical answer is more modest and more achievable. Cities that have improved their measurement did three things: deployed a distributed low-cost sensor network with enough density to resolve neighbourhood differences, calibrated it against the official station rather than replacing that station, and rewrote activation thresholds to trigger on the hottest monitored areas rather than the city average.

The cost is small relative to any capital programme it informs. The institutional obstacle is larger, because it requires accepting that the number the city has been reporting for decades was not describing what residents experienced.

The accountability angle

There is a reason some administrations are slow to adopt better measurement, and it is worth stating directly. Denser monitoring produces a higher count of threshold exceedances, more declared emergency days, and a documented record of which neighbourhoods bear the load.

That record creates obligations. It also creates the evidence base needed to justify the spending, which is why the cities furthest along on measurement tend to be the ones that have already committed capital and need to defend it.

For the generation-side infrastructure that heat demand strains, see our reporting on why storage is stuck in the interconnection queue.