Possible influence of human activity on the daily maximum precipitation events over the Three-River Headwaters region of the Tibetan Plateau.

The Three-River Headwater (TRH) region, located in the hinterland of the Tibetan Plateau (TP), has experienced significant wetting since the early 2000s. However, the potential contribution of external forcings to the growing frequency of extreme precipitation events in this area has been rarely examined. Here, we conduct an analysis on the change in daily maximum precipitation (Rx1day) in the TRH region, with a focus on the anomalous event in 2023, and an investigation into the influence of external forcings on the occurrence probability of the Rx1day events. The results indicate that extreme precipitation has increased in the TRH region, particularly after the early 2000s, with a record anomalous Rx1day event in 2023. Further analysis suggests that anthropogenic forcings may have reduced the probability of Rx1day events in general, though greenhouse gases have increased atmospheric water vapor, offsetting the effect of anthropogenic aerosols. And aerosol forcing inhibits Rx1day events mainly through dynamic processes. However, the occurrence probability of a 2023-like anomalous Rx1day event may have been primarily related to anthropogenic factors, with greenhouse gases playing a key role by enhancing atmospheric moisture. This study emphasizes the crucial role of anthropogenic forcings in precipitation extreme in the TRH region.