Simulation Analyses Of The Influences Of Volcanic Eruptions On Decadal Drought In Eastern China

In recent years,extreme drought occurs frequently over the world,casting profound impacts on social economy and people's life.Eastern China,as a typical monsoon domain in East Asia(EA),is one of the most severe drought-stricken areas over the world,receiving widespread attention in contemporary society.Previous studies have shown that drought in eastern China is influenced by both internal variability and volcanic forcing.Moreover,volcanic eruptions can strongly influence rainfall changes and intensify and extend drought if superimposed on drought events due to internal variability.However,whether volcanic eruptions occurring in different drought phases and with different magnitudes have similar impacts on the persistency and intensity of drought remains unclear.In this paper,using proxy reconstructed precipitation and simulated data from the Community Earth System Model-Last Millennium Ensemble Project(CESM-LME)archive,we explored the effects of volcanic eruptions occurring in different drought phases with different magnitudes on drought.Also,based on the Community Earth System Model(CESM),we performed severe groups of volcanic sensitivity experiments in which volcanic eruptions take place in the late,middle and early phases of drought and with divergent magnitudes(i.e.25 Tg,50Tg and 100Tg).On account of this,spatial analysis(such as window analysis,multi-data and multi-element composite analysis)and spatial statistical analysis(such as spatial interpolation and regression analysis)are used to analyze the spatial and temporal variations and the mechanisms behind the volcano-induced droughts.Furthermore,to deeply understand the influences of volcanic eruptions and the interactions between internal climate variability and external volcanic forcing,we explore the evolution characteristics and mechanisms of the Ming Dynasty Megadrought,the most severe drought in China in the past millennium,as case study.This study shows that the persistence and severity of drought varies if volcano erupts in different drought phases.After late-phase volcanic eruptions,the volcanoinduced droughts are the severest and persist the longest,while middle-phase eruptions cause droughts with smaller magnitudes.When volcanic eruptions occur in the early phase of the drought,the dry conditions are the least severe.The mechanisms can be explained by the direct and indirect impacts of volcanic eruptions on drought respectively.On one hand,the intensity of drought is highly related to the different land-sea heat contrast after volcanic eruptions with different magnitudes.When volcano erupts in the late phase of a drought,there exist the largest land-sea thermal contrast changes,giving rise to largest magnitudes of EASM weakening and precipitation decreases,and vice versa.The intensity of drought is influenced by the anticyclone anomalies in china's eastern coastal area and the northern and central part of Japan as well.On another hand,the persistence of the volcano-related drought is mainly controlled by the recovery rates of soil moisture and West Pacific Subtropical High(WPSH)after volcanic eruptions.After late-and middle-phase volcanic eruptions,the recovering rates of soil moisture and WPSH are relatively slower,giving rise to longer duration of droughts,and vice versa.In this study,the effect of volcanic activities with different magnitudes on droughts is studied.Volcanism with an intensity smaller than 25 Tg is too weak to significantly influence the precipitation changes,while 50 Tg volcanic eruptions can strongly prolong and intensify droughts over Eastern China.The severity of rainfall deficit increased with the increasing of volcanic magnitude linearly.On one hand,as the increasing of volcanic magnitude,the ocean–land thermal contrast becomes larger,which induced larger sea level pressure between land and sea and thus gave rise to severer dry conditions.On another hand,the lager the volcanic magnitude is,the slower the recovery rate of the WPSH and sea surface temperature(SST)will be afterwards,causing longer duration of drought extensions,and vice versa.This study also show that,the Ming Dynasty Mega-drought(MDMD,1637-1643),one of the most severe drought events in China in the last millennium,is a typical drought that influenced by both internal climate variability and external volcanic forcing.The Ming Dynasty Mega-drought is firstly triggered by a natural drought event starting in 1637,and then intensified and extended by the tropical volcanic eruption at Mount Parker in 1641 for about 3 years.The mechanisms can be explained by the direct and indirect impacts of volcanic eruptions on drought,respectively.It was demonstrated that the intensification of drought after Mount.Parker was caused by a weakening East Asia summer monsoon(EASM),and the monsoon failure was associated strongly with the decreased land–ocean thermal contrast,the negative soil moisture response,the weakening and eastward retreating WPSH,along with the anomalous cold SST in China's eastern coastal areas.