摘要 地表干湿变化是气候研究的热点问题。本研究利用一个古气候瞬变模拟试验的数据，采用降水与潜在蒸散量（PET）之比所定义的干湿指数（AI），研究了过去21 ka中国地表干湿状况演变特征。就中国区域平均而言，气候在10 ka B.P.以前总体偏湿，之后则逐渐变干。决定干湿变化的外强迫因子随时间而变。22~19 ka B.P.，AI受低温室气体浓度和大陆冰盖影响，比目前高22%；19~10 ka B.P.，AI随温室气体浓度增加和大陆冰盖融化而逐渐降低，同时随着北半球高纬夏季日照量增大而升高，总体上维持在末次冰盛期的水平；10 ka B.P.之后，AI受控于轨道强迫，逐步降低至目前水平。在过去21 ka，AI变化总体上由PET主导：温室气体浓度、轨道参数分别通过影响近地面气温和相对湿度来改变PET大小；而在冰盖强迫下，PET变化源自气温和相对湿度的联合作用。与轨道尺度变化不同，气候在千年尺度冷事件期间总体偏干，变化主因是降水减少。空间上，AI变化有明显地域差异，不同地区AI变化的主导因子、对相同外强迫的响应形式各不相同。
Abstract：The terrestrial moisture change is one of the hot issues in climate change researches. This study investigates the dry-wet changes over China through the last 21 ka and associated main climatic drivers using data from a transient simulation, which is forced by realistic climatic drivers consisting of orbital parameters, greenhouse gas(GHG) concentrations, continental ice sheets, and meltwater fluxes. The aridity index(AI), as defined by the ratio of annual precipitation to potential evapotranspiration(PET), is used to measure the moisture conditions, where PET is calculated according to the Penman-Monteith equation. Main conclusions are as follows.
(1) At the orbital scale, the dominant external forcing exerting on AI varies with time. On average, the China climate is relatively humid before 10 ka B.P., and then has a drying trend. To be specific, during the period 22~19 ka B.P., AI is 22% higher than present as induced by the lower GHG concentration and ice sheet expansion; in the following 9 ka, the GHG concentration increase and ice sheet melting favor a rise of AI, but in the meantime the increased summer insolation in the northern high-latitudes leads to AI reduction, and thus the AI is overall little changed; thereafter, AI varies under the domination of transient orbital parameters and gradually decreases to the current level. (2) Further diagnostic is conducted to examine main variables responsible for AI changes through decompositions of AI and PET functions. The diagnostic reveals that the aforementioned orbital-scale changes in AI are determined by the altered PET:the GHG concentration and orbital parameters affect PET mainly through altering near-surface air temperature and relative humidity, respectively; under the control of the ice sheet, PET changes are due to the combined effect of air temperature and relative humidity changes. (3) The millennium-scale change is different from that at the orbital scale, and the climate is drier during abrupt cold events due to lower precipitation. (4) Spatially, the changes are regionally different across China, with the external forcing dominating AI changes and the AI responses to the same forcing varying among regions.
刘珊珊, 姜大膀. 过去21 ka中国干湿变化的瞬变模拟分析[J]. 第四纪研究, 2020, 40(6): 1550-1561.
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2020, Vol. 40 
