基于CMIP6模式对青藏高原平均降水的模拟评估与预估

CMIP6 evaluation and projection of precipitation over the Qinghai-Xizang Plateau

青藏高原降水对区域气候和水循环有着重要影响,在全球变暖的大背景下,研究青藏高原的降水分布及趋势变化十分必要.以1995-2014年青藏高原观测降水为基准态,评估第六次国际耦合模式比较计划(CMIP6)中20个模式对青藏高原年和季节平均降水的模拟能力.结果表明,CMIP6模式能够较好地模拟出青藏高原降水从东南向西北减少的空间分布特征,但模式模拟仍存在湿偏差,平均降水偏差达到1.3 mm·d^(-1).而且对于冬季模拟降水,模式之间存在较大的差异,模式标准差在3 mm·d^(-1)以上.在共享社会经济路径SSP5-8.5和SSP2-4.5情景下,基于20个模式的模式集合(AMME)与择优选取的五个模式组成的集合(BMME)对中期(2045-2065年)和长期(2081-2100年)平均降水的未来预估,整体上青藏高原未来降水将有所增加,SSP5-8.5情景增幅大于SSP2-4.5,长期降水增幅大于中期.中期降水变化与长期分布一致,除了冬季和秋季南部地区、夏季东部地区表现为降水减少之外,其他大部分地区表现为全年和季节平均降水量的增加.BMME预估全年和季节平均降水增幅往往大于AMME.未来年平均降水的增加主要来源于春季降水的增加.

Precipitation over the Qinghai-Xizang Plateau(QXP)has a significant impact on regional climate and water cycling.Understanding the impact of global warming on the trend of precipitation over the QXP is crucially important.This article assesses the simulation results of 20 Coupled Model Inter-comparison Project Phase 6(CMIP6)models with the gridded observations for the period of 1995-2014 to evaluate the performance of CMIP6 models in simulating precipitation over the QXP.The results indicate that the CMIP6 models reasonably capture the spatial distributions of precipitation on the QXP,which decrease from the southeast to the northwest,but the model simulations still suffer from wet bias,the mean precipitation bias is 1.3 mm·d^(-1).And there is a large model spread of simulated winter precipitation,the standard deviation is larger than 3 mm·d^(-1).Under the scenario of the Shared Socio-economic Pathway SSP5-8.5 and SSP2-4.5,future projections of precipitation in the mid-term(2045-2065)and long term(2081-2100)based on the ensemble of 20 models(AMME)and the ensemble of 5 optimal models(BMME)show that the future precipitation over the Qinghai-Xizang Plateau is expected to increase,with larger increases under SSP5-8.5 than under SSP2-4.5,and larger increases in long term than mid-term.Spatially,the mid-term precipitation changes align with the long-term,with most areas showing increases in year-and seasonal-averaged precipitation,except for the southern portion of the region in winter and fall,and the eastern portion of the region in summer,which show decreases in precipitation.Notably,BMME projections tend to be higher magnitudes of increase in both annual and seasonal precipitation compared to the AMME.In future scenarios,the increase of annual precipitation is predominantly attributable to the increase of springtime rainfall.