The modern “wet” tropics are dominated by the Intertropical Convergence Zone, however “dry” tropics likely occurred in Earth’s history. It is unclear how the tropics change between wet and dry climates because recent progress has focused on modern and warmer climates. We show the tropical hydrological cycle undergoes a wet-to-dry regime transition when surface wetness is decreased in a general circulation model. The dry regime occurs when precipitation is suppressed by negative evaporation. The regime transition is dominated by near-surface relative humidity, in contrast to our traditional understanding which assumes changes in relative humidity are small. We show near-surface relative humidity changes are controlled by re-evaporation of stratiform precipitation. The moistening effect of re-evaporation is non-local: re-evaporation happens near the lifting condensation level and moisture diffuses downward to the near-surface. Our results provide a first step toward understanding tropical hydrological cycle changes between wet and dry climates.