Response of summer precipitation over the Tibetan Plateau to large tropical volcanic eruptions in the last millennium

Changes in summer precipitation over the Tibetan Plateau (TP) significantly influence the surface runoff, river discharge and water availability for the downstream Asian countries, which is sensitive to external forcing. But its response to volcanic eruptions remains unknown. Here we investigate the summer precipitation changes after tropical volcanic eruptions over the TP region by using multiple lines of evidence including reconstructions over the last hundreds of years, observations during recent decades and model simulations covering the last millennium. Both the instrumental data and reconstructions reveal a significant reduction in summer precipitation over the southern TP region during the first summer following tropical volcanic eruptions, which are further confirmed by the coupled model simulations driven by volcanic forcing. The model results indicate that both the dynamic processes related to atmospheric circulation changes and the thermodynamic processes related to specific humidity changes contribute to the decreased precipitation in the southwestern TP, while the thermodynamic process dominates the reduction of precipitation in the southeastern TP. The thermodynamic process results from decreased atmospheric precipitable water caused by decreased surface temperature after tropical volcanic eruptions. The dynamic processes are caused by increased gross moist stability, spatial distribution of surface cooling and a southward shift of westerlies related to weakening and shrinking of Hadley circulation following tropical eruptions. Our results imply that major tropical eruptions have significant impact on the summer precipitation over the southern TP regions, which will further decrease the source of supply for the TP glaciers and runoff output.