Attributing Extreme Precipitation Characteristics in South China Pearl River Delta Region to Anthropogenic Influences Based on Pseudo Global Warming

In the context of human-induced warming climate, the atmosphere is expected to hold a greater amount of water vapor, leading to heavier precipitation on a global scale. However, the extent to which changes in extreme rainfall can be attributed to human influences varies at regional scales. Here we conduct attribution analyses on 40 extreme precipitation events in different seasons during 1998-2018 over the Pearl River Delta (PRD), by using the Weather Research and Forecasting (WRF) model and applying the pseudo global warming (PGW) method. The model was integrated with the factual and counterfactual conditions separately, with the latter derived from differences between the Coupled Model Intercomparison Project Phase 5 (CMIP5) historical and historical-natural runs. By comparing parallel experiments, extreme daily rainfall (>95th percentile) in PRD enhanced by 8%-9.5% for 0.9-1.1 K near-surface warming (nearly Clausius-Clapeyron, or CC scaling) in the May-to-September (MJJAS) and 12.4% at most for 0.6-0.8 K warming (similar to 2 x CC rate) in non-MJJAS seasons; the probability of those extremes increased by 10%-30% during MJJAS (20%-40% in other seasons). While moisture-related thermodynamic effects play a similar role in modulating rainfall, the wind circulation-related dynamic effects act differently in different seasons. Changes in MJJAS extremes are related to stronger low-level southerly winds, while non-MJJAS rainfall is exacerbated by strengthened low-level wind convergence and updrafts. Moisture budget analysis suggests that thermodynamic effects associated with the increased moisture amount account for the mean rainfall increase, whereas dynamic effects related to wind circulation changes are responsible for extreme precipitation, regardless of seasons.