On the hottest day of the summer, walkers on 72% of Milton Keynes' footpaths faced very strong heat stress.

How this was made

Environment Agency lidar flown in the winters of 2019–20 and 2020–21 gives the shape of the whole area. A custom deep-learning model sorts its points into ground, buildings, trees and water. SOLWEIG (Lindberg et al. 2008) then follows the sun over those buildings and trees hour by hour on 13 August 2026 and works out the radiant heat a person takes in on each 1 m square. With each hour's air temperature, humidity, wind and sunshine from the Met Office's 2 km UKV model, that gives the feels-like temperature (UTCI). Footpaths are from OpenStreetMap and bus stops from NaPTAN; places built since the flight are greyed. New trees are placed as TreePlanter does (Wallenberg et al. 2022). Very strong heat stress starts at a UTCI of 38 °C: walking in it, the body's core temperature starts to rise within half an hour (Błażejczyk et al. 2013). Risk to health starts lower, from 26 to 32 °C in much of Europe (Di Napoli et al. 2018), but on 13 August every footpath reached 32 °C at some hour, so the map marks 38 °C, where shade still made the difference. The lidar was flown in winter, when bare fields can read as paving, so farmland may be modelled warmer than it was.

© OpenStreetMap contributors · Protomaps · Lidar © Environment Agency · NaPTAN © DfT · Contains OS data © Crown copyright and database right 2026 · Boundary: ONS · Weather: Met Office UKV (CC BY-SA 4.0), weather data by Open-Meteo.com · MapLibre

The code and its references: github.com/JacobWeinbren/mk-heat