全球极端降水对不同外强迫的敏感性响应:基于PDRMIP模拟试验

Sensitivity of global extreme precipitation to different climate forcings:A PDRMIP multimodel study

全球增暖背景下极端降水变化受到了温室气体、太阳辐射、气溶胶等自然与人为强迫因素的共同影响.本文基于“降水驱动与响应模式间比较计划”(A Precipitation Driver and Response Model Intercomparison Project,PDRMIP)提供的9个全球气候模式模拟的针对5种不同因子(加倍二氧化碳、增加2%的太阳辐射、10倍黑碳、5倍硫酸盐、3倍甲烷)高强迫情景下的理想试验,利用气候变化检测和指数专家组(Expert Team on Climate Change Detection and Indices,ETCCDI)定义的4个降水指数,详细分析了不同外部强迫因子作用下全球极端降水的响应.结果表明,相比于平均降水,在5种强迫因子作用下极端降水指数均表现出更大的变化.与加倍二氧化碳相比,增加2%的太阳辐射、5倍硫酸盐气溶胶和3倍甲烷强迫下全球极端降水对温度变化的响应更加强烈,而10倍黑碳气溶胶强迫下的降水变化则表现出较强的模式间差异.在加倍二氧化碳、增加2%的太阳辐射和3倍甲烷强迫下,极端降水的变化表现相似的纬向分布特征,最强的降水响应出现在赤道地区;10倍黑碳、5倍硫酸盐气溶胶强迫下则表现出明显的南北半球差异.水汽收支诊断结果揭示了在高强迫情景下,二氧化碳、太阳辐射和甲烷强迫下热带地区更强烈的降水变化主要与热力作用有关,而动力作用可能是导致黑碳、硫酸盐气溶胶强迫下降水变化的主要原因.

Under the current global warming condition,changes in global extreme precipitation have been influenced by both natural and anthropogenic climate forcings—e.g.,greenhouse gases,solar irradiation,and aerosols.In recent years,global precipitation has experienced significant changes,with more intense and frequent extreme rainfall events often leading to serious natural hazards,which in turn result in huge economic losses as well as adverse impacts on human safety and social development.Compared to mean precipitation,extreme precipitation has higher sensitivity to the same surface temperature changes and shows a range of responses that depend largely on differences in climate forcing.Several studies have revealed more robust precipitation changes in response to aerosols and solar irradiation than greenhouse gases,but how individual climate forcings affect the changes in extreme precipitation remains poorly understood.Thus,understanding how extreme precipitation responds to the perturbations of each individual forcing will enhance our understanding of the physical mechanisms behind the variations in extreme precipitation.In this study,we present multi-model results under the framework of the Precipitation Driver and Response Model Intercomparison Project(PDRMIP),which aims to investigate the responses of extreme precipitation to perturbed climate forcings via the following scenarios,a doubling of the CO2 concentration(CO2×2);a 2%increase in solar insolation(SOL+2%);a 10-fold increase in black carbon concentrations or emissions(BC×10);a 5-fold increase in SO4 concentrations or emissions(SO4×5);and a tripling of CH4 concentrations(CH4×3).The sensitivity and spatial patterns of extreme precipitation under these different external forcings were calculated.Using the moisture budget equation,we further diagnosed the impacts of moisture humidity and atmospheric circulation on precipitation and quantified the relative contributions of dynamics and thermodynamics to significant latitudinal bands of precipitation under individual forcings.For the same degree of changes in surface temperature,the results show that more robust responses of extreme precipitation are simulated under all five forcings compared to mean precipitation,suggesting higher sensitivities of extreme precipitation.Compared to the CO2×2 experiment,the simulations of perturbed solar insolation,SO4,and CH4 produce more robust precipitation changes.For these four forcings,there is a high consistency between individual models,while for the BC×10 experiment,there is larger inter-model uncertainty.It was also found that there are similar zonal mean distributions of precipitation sensitivity under the CO2×2,SOL+2%,and CH4×3 forcings,with the maximum positive values mainly located in the equatorial region of the tropics,and opposite changes in subtropical regions.Significant hemispheric asymmetry occurs in the simulations under the perturbed BC and SO4 scenarios.It is clearly shown that there are increasing precipitation trends in tropical regions,both in the perturbed BC and SO4 experiments,while decreasing precipitation trends are mainly located over the southern subtropical oceans under the SO4×5 forcing,with less rainfall in the northern mid-to-high latitudes and southern subtropical regions for the perturbed BC simulation.Analysis of the moisture budget suggests that thermodynamic processes contribute to the larger changes in precipitation in tropical regions under the CO2×2,SOL+2%,and CH4×3 forcings,whereas dynamic changes(especially robust vertical motion)are the main reason for stronger precipitation responses in the perturbed BC and SO4 simulations.These findings provide a full understanding of the climate responses and physical processes of extreme precipitation under different external forcings,which is beneficial for policy-making in relation to climate mitigation and adaptation,as well as verification of model simulations.