<p>Climate models largely assume uniform intensified tropical cyclone precipitation under global warming, overlooking critical local-scale variability. Analyzing 366 tropical cyclones that affect South China (1979–2018), we show that urbanization and local-scale storm characteristics strongly modulate regional climate signals in determining terrestrial rainfall trends. A pronounced spatial heterogeneity emerged: the Pearl River Delta megacity and western regions experienced 20–35% increases in tropical cyclone rainfall (1999–2018 versus 1979–1998), while eastern areas saw 10–20% decreases. This spatial pattern is primarily driven by variations in local storm track density, duration, and intensity (150-km scale). Shapley value decomposition reveals that local storm characteristics and urbanization jointly explain over 55% of the variance in coastal rainfall. Urban development further creates a compound hazard in the Pearl River Delta megacity: enhanced rainfall 48–96 h after storm passage, generating cascading disaster risks when urban infrastructure is most vulnerable. Our findings underscore the need for local-scale (50–100 km) adaptation and risk assessment strategies for coastal cities globally, as over a billion people are expected to live in coastal megacities by 2050.</p>