Causes of large projected increases in hurricane precipitation rates with global warming

Recent climate modeling studies point to an increase in tropical cyclone rainfall rates in response to climate warming. These studies indicate that the percentage increase in tropical cyclone rainfall rates often outpaces the increase in saturation specific humidity expected from the Clausius-Clapeyron relation (~7% °C −1 ). We explore the change in tropical cyclone rainfall rates over all oceans under global warming using a high-resolution climate model with the ability to simulate the entire intensity spectrum of tropical cyclones. Consistent with previous results, we find a robust increase of tropical cyclone rainfall rates. The percentage increase for inner-core tropical cyclone rainfall rates in our model is markedly larger than the Clausius-Clapeyron rate. However, when the impact of storm intensity is excluded, the rainfall rate increase shows a much better match with the Clausius-Clapeyron rate, suggesting that the “super Clausius-Clapeyron” scaling of rainfall rates with temperature increase is due to the warming-induced increase of tropical cyclone intensity. The increase of tropical cyclone intensity and environmental water vapor, in combination, explain the tropical cyclone rainfall rate increase under global warming. Climate change: Tropical cyclone rainfall rate increases depend on temperature and intensity change The rainfall associated with tropical cyclones (TCs) is a key component of their ultimate destructive potential. TC rainfall rates are projected to increase under global warming, due in part to the consequence that a warmer atmosphere holds more water vapor and permits higher moisture convergence. But future change in TC intensity, or wind speed, can also affect moisture convergence and resultant rainfall rates. Maofeng Liu of Princeton University, USA, and colleagues used a high-resolution climate model to understand important factors in TC rainfall rate change. They calculated increased rainfall rates of 13–17% per degree Celsius change — over twice the theoretical rate of approximately 7% from temperature increases, alone. This result suggests that atmospheric water vapor increase due to temperature increases alone cannot fully account for TC rainfall rate changes, and that increased storm intensity is also crucial. A resampling technique confirmed this hypothesis. These results underscore the need for better projections of the response of TC intensity to warming.