Attributing extreme precipitation characteristics in South China Pearl River Delta region to anthropogenic influences based on pseudo global warming

In the context of the 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 recent changes in extreme rainfall can be attributed to human influences varies at the regional scale. Here we conduct attribution analyses on 40 extreme rainfall events that occurred 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, PRD near-surface temperature has been raised respectively by 0.9-1.1 K in the May-to-September (MJJAS) and 0.6-0.8 K in non-MJJAS seasons. Accordingly, extreme daily rainfall (> 95th percentile) increased by 8%-9.5% (~Clausius-Clapeyron, or CC scaling) in MJJAS and 12.4% at most (~2 CC rate) in non-MJJAS season. For the same extreme thresholds, the probability of occurrence increased by 10%-30% during MJJAS (20%-40% in non-MJJAS season). While moisture-related thermodynamic effects play a similar role in modulating rainfall, the dynamic effects (due to circulation changes) 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.