Delhi recorded a blistering 43.5°C yesterday, but the real story lies in how that temperature is perceived. The heat index, a measure of how hot it actually feels when humidity is factored in, exceeded 50°C in several parts of the city. This discrepancy between raw temperature and human experience has been better predicted by UK climate models than by their US counterparts, raising questions about which datasets should inform adaptation policies.
Dr. Arjun Mehta of the Indian Institute of Tropical Meteorology noted that the UK Met Office's HadGEM3 model, which incorporates more granular urban heat island effects and soil moisture data, accurately forecast the extreme heat index a full 72 hours in advance. In contrast, the US GFS model underestimated the heat index by up to 6°C. This is not a one-off anomaly. A recent study in Geophysical Research Letters found that for South Asian heatwaves, UK models consistently outperform US models by an average of 15% in predicting wet-bulb temperature, a key metric for human survivability.
The implications are stark. As the planet warms, heatwaves become not just hotter but more humid. The combination can push the human body beyond its ability to cool itself. The UK's approach, which prioritises high-resolution land surface processes, captures this more effectively than the US models, which are tuned for global-scale dynamics. This matters for billions living in the tropics.
Policy makers in the developing world have been forced to rely on a patchwork of data. The Delhi heatwave is a case study in why this must change. The UK Met Office has offered to share its regional modelling expertise, but political and financial hurdles remain. Meanwhile, the heat is not waiting. Every fraction of a degree of avoided warming is a life saved. The evidence is clear: we must use the best tools available, and right now, they are British.
