多模式预估的21世纪中国降水季节性变化存在区域差异

[发布日期: 2023-11-17 浏览量 1112]

【中文介绍】

在全球变暖背景下，降水的许多方面均已发生了明显变化，且预估表明其在未来还将持续变化。然而，以往研究多关注降水变化的其他特征，而较少关注降水季节性的未来变化。事实上，了解区域尺度上的降水季节性未来变化及其相关机制对于减缓和适应气候变化至关重要。

因此，课题组基于32个CMIP6模式，采用两种常用的降水季节性指数研究发现，相对于1995−2014年，2081−2100年无量纲季节性指数DSI在中国几乎所有地区均增强，幅度存在区域差异，其中东南部和青藏高原南部增强明显，而西北部变化较弱；在SSP2-4.5和SSP5-8.5情景下，多模式集合中位数（第25−75百分位）显示中国平均增强了15%（7%−21%）和23%（15%−29%）。而相对季节性指数SI的未来变化显示出较大区域差异，其在中国北部减小、南部增大，造成中国区域平均变化不大。DSI和SI的变化分别与降水绝对值和相对比例的变化在不同季节间分布不均有关。进一步分析表明，不同水汽收支项对降水变化的贡献因季节而异，造成降水的季节分布发生变化，从而导致DSI和SI的变化。具体而言，垂直水汽平流的热力项主要决定了中国大部夏季降水增幅大于冬季，从而导致DSI变化。残差项主导了中国南部冬季降水减少，导致在给定的年降水量下，降水更多集中在夏季，从而使得SI增大；而中国北部与之相反。

【英文介绍】

Under the background of global warming, many aspects of precipitation have already changed significantly, and projections indicate that they will continue to change in the future. However, previous studies mainly focused on changes in other characteristics of precipitation, with less emphasis on its seasonality. In fact, understanding precipitation seasonality change and the associated mechanism at regional scale is crucial for mitigation and adaptation to climate change.

Therefore, based on historical simulations and projections under two scenarios of SSP2-4.5 and SSP5-8.5 provided by 32 models from the CMIP6, we investigate the future precipitation seasonality changes over China by two indices, the dimensionless seasonality index (DSI) and the relative seasonality index (SI), and the associated physical mechanisms by moisture budget diagnosis. The results show that relative to the baseline period 1995−2014, the DSI is enhanced across almost all of China during the period 2081−2100, with stronger magnitudes in southeastern China and the southern Tibetan Plateau and weaker magnitudes in northwestern China, and national-mean enhancements are 15% (7%−21%) and 23% (15%−29%) for the multimodel median (25th−75th percentile range across models) under the SSP2-4.5 and SSP5-8.5 scenarios, respectively. Projected SI changes show large regional differences, with decreases in northern China and increase in southern China, leading to little change for the national mean. The DSI and SI changes are associated with uneven distributions of changes in absolute amounts and relative proportions of precipitation among seasons, respectively. Further analysis reveals that the contributions of different moisture budget terms to precipitation changes vary across seasons, resulting in changes in the seasonal distribution of precipitation and thus the DSI and SI changes. Specifically, the thermodynamic component of vertical moisture advection primarily determines the greater magnitude of increased precipitation in summer than in winter in most of China, resulting in the DSI change. The reduction in residual term dominates the diminished winter precipitation in southern China, leading to more precipitation concentrated in summer for given annual precipitation and thus the intensification in SI, while the opposite holds true in northern China.

【关键图表】

图：多模式集合中位数模拟的1995−2014年中国降水季节性指数（a，d）及其在2081−2100年的变化（b−c，e−f）：（a−c）为无量纲季节性指数DSI，（d−f）为相对季节性指数SI；（b，e）为SSP2-4.5情景，（c，f）为SSP5-8.5情景。右上角数值代表中国区域平均值，斜线区表示70%以上模式结果与多模式集合中位数变化符号一致，（e，f）中紫色和红色矩形框分别表示中国北部（32°N−42°N, 100°E−120°E）和南部（22°N−32°N, 100°E−120°E）

【引用格式】

Hu, D., Z. Tian, X. Lang, and D. Jiang, 2023: Regional difference in precipitation seasonality over China from CMIP6 projections. International Journal of Climatology, 43, 6179–6190.