After another spell of wet weather along Australia’s east coast, with storms, heavy rain and flash flooding across Sydney and parts of New South Wales, it is natural to ask whether our cities are shaping the rainfall that descends upon them.

This matters because most people now live in cities. If urbanisation changes rainfall, even slightly, the effects can reach large populations through flooding, stormwater design, water supply and infrastructure planning.

Satellite data have consistently shown that many cities experience more rain events than the countryside around them. The usual explanation is that cities themselves are involved: urban heat, rougher surfaces, aerosols and changed land cover can all affect how storms develop and where rain falls.

Our new study, published in Environmental Research Letters, asks a related question: how much of this data reflects real changes in rainfall, and how much depends on how we observe it?

Why we need satellites

Understanding rainfall over cities is hard.

Rain gauges accurately measure rainfall at a specific location, but are irregularly distributed and cannot fully capture how rain varies across a large city. Climate models can simulate urban weather in detail, but kilometre-scale simulations across many cities and decades remain computationally........

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