Climate / Data EngineeringClimate Twin Frankfurt

Is Frankfurt actually warmer than the countryside around it? We measured it.

Stable release: Climate Twin Frankfurt v1.0.0. The product is stable; the preregistered v0.1 paired-station study remains unchanged and reproducible.

The question

"Cities are warmer than their surroundings" is one of the most repeated facts in climate communication — the urban heat island effect. It's real, well-documented globally, and also frequently stated without a number, a source, or an uncertainty range attached. We asked a narrower, answerable version for one specific city: how much warmer is urban Frankfurt than its designated rural reference station, with an actual confidence interval, and has that gap changed over the last four decades?

What we actually did

Germany's national weather service, DWD, operates a real program pairing urban climate stations with rural reference counterparts. We used their own designated Frankfurt pair — Frankfurt/Main-Westend (inner-city) against Frankfurt/Main (physically the airport, which we disclose rather than pretend is a pristine rural village) — across every day both stations recorded a valid reading from November 1985 through December 2025: 14,579 days.

What we found

The estimated gap is modest: +0.455°C on average (30-day block-bootstrap 95% interval 0.432 to 0.478). That supports a warmer average at Westend relative to this specific airport reference, conditional on the two station histories and the chosen block method—not a city-wide causal urban-heat-island estimate. The preregistered classical OLS trend is not statistically distinguishable from zero (p = 0.118). Because its annual residuals are serially correlated, a post-release three-lag Newey–West sensitivity is preferable for uncertainty: 95% interval −0.0079 to +0.0016°C/year, p = 0.186. The conclusion remains "no linear trend detected," not "no trend exists."

We also built something concrete out of the two stations' real coordinates: an interactive map computing the true straight-line distance (15.42 km) and bearing between them directly from their published locations — no map imagery library, just real trigonometry on real numbers.

Try it yourself

The interactive site shows the full daily and seasonal breakdown, the year-by-year trend with its own confidence band, and the station map — uncertainty stated before any "warmer" or "trending" conclusion, the same discipline as every project in this series.

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