Tropical Radiation-Precipitation Relationship and Future Extreme Precipitation Constraint

Over the tropics, a robust statistical relationship between radiation and precipitation underscores the convection conversion efficiency associated with the cloud-radiative effect in a certain climate state. In this study, we define an "RP ratio", a metric derived from outgoing longwave radiation and precipitation anomalies, for linearly estimating the radiation-precipitation relation (RP relation). The RP ratio exhibits significant disparities across global climate models (GCMs), with the majority overestimating it relative to the observation.

Since the RP ratio and future extreme precipitation (EP) are found to be highly correlated over the tropics, an emergent constraint (EC) on the hydrological cycle projections is applied based on this correlation. The EC in this study shows its novelty due to the first application of the RP relation on hydrological cycle projections. According to the EC results, we find the fractional increase in the 99.9th percentile of EP by the end of the 21st century is lowered from 28% to 14% (from 16% to 5%), with the uncertainty reducing by 22% (12%), under the high-emission scenario (median-emission scenario). Overall, the GCMs underestimate the future tropical EP while overestimating its fractional increase. The results provide valuable insights for model improvement and better climate adaptation planning.