基于CMIP5模拟的中国区域陆气耦合强度评估及未来情景预估

Projection and Evaluation of the Land–Atmosphere Coupling Strength over China by CMIP5 Models

基于第五次国际耦合模式比较计划(CMIP5)11个模式历史情景的模拟结果计算得到了中国区域夏季的陆气耦合强度并进行集合平均,结果表明,位于半干旱区的华北和内蒙古地区陆气耦合强度相对较强,西部干旱区的陆气耦合强度相对较弱,位于湿润区的中国东北地区东部、长江中下游和西南地区陆气耦合强度最弱。利用上述模式集合平均结果与由NCEP再分析资料和欧洲中心的中期气象预报40年再分析资料(ERA40)计算得到的陆气耦合强度相比较,结果显示这些模式的集合平均与再分析资料NCEP和ERA40的计算结果有较好的一致性。利用历史情景模拟和不同的典型排放路径(RCP),即低排放情景RCP2.6、中排放情景RCP4.5和高排放情景RCP8.5下的模拟结果预估陆气耦合强度未来变化。结果显示:与历史情景相比较,位于湿润区的中国南方地区蒸散发的主要控制因子是温度,在3种排放情景下随着温度上升引起蒸散发增加所导致陆气耦合强度升高;位于青藏高原以及半干旱区的内蒙古大部分地区蒸散发在未来的年际变化幅度减弱导致陆气耦合指数降低;位于西北干旱区陆气耦合强度在RCP2.6和RCP4.5情景上升,然而在RCP8.5情景下陆气耦合强度下降,其原因是在高排放情景下,水汽平流输送明显增强,局地蒸散发异常对空气湿度变化的贡献减弱,导致了陆气耦合强度降低。未来预估结果在中国南方可信度相对较高,从全国来看,在RCP4.5情景下可信度相对较高。

The ensemble mean summer land–atmosphere coupling strength of eleven models from the CMIP5（Coupled Model Intercomparison Project, phase 5）, performing the historical run in China, is calculated. The results show that the strength is relatively high in Huabei and Inner Mongolia, located in the semi-arid area, and the result in West China, located in the arid area, is second strongest. The lowest strength regions are the humid areas of eastern Northeast China,the middle and lower reaches of the Yangtze River, and Southwest China. Comparison of the ensemble mean with results calculated from NCEP and ERA-40（European Centre for Medium-Range Weather Forecasts 40-Year Reanalysis） data shows high consistency. Next, the ensemble mean of the CMIP5 historical run and three RCP（Representative Concentration Pathway） runs（RCP2.6, RCP4.5, and RCP8.5） are used to predict the change in the strength of summer land–atmosphere coupling in China. The results show, compared to the historical run, the strength increases in the humid area of southern China, induced by higher evapotranspiration caused by higher temperatures. Meanwhile, the strength reduces in the Tibetan Plateau and semi-arid area of Inner Mongolia, induced by a reduction in the land–atmosphere coupling index caused by a reduction of evapotranspiration amplitude. The arid area of Xinjiang shows increasing strength in the RCP2.6 and RCP4.5 runs, but decreasing strength in the RCP8.5 run. This result is caused by enhanced vapor advection in the high emissions scenario, which makes the relationship between local evaporation and air humidity weaker. There is a higher degree of confidence in the prediction results in southern China and in the RCP4.5 run.