基于模式优选的21世纪中国气候变化情景集合预估

Ensemble projection of climate change scenarios of China in the 21st century based on the preferred climate models

未来气候变化情景预估是制定气候变化应对和适应策略的科学基础。本文利用参与耦合模式比较计划第五阶段(CMIP5)的30个气候模式的模拟数据,通过评估各模式对历史气候变化的模拟能力,筛选出模拟区域气候变化的最优模式组合,进而建立偏最小二乘回归(PLS)集合预估模型,据此利用最优模式模拟结果预估区域温度和降水变化情景。通过与历史数据的对比,研究发现本文基于最优模式建立的PLS集合预估模型不仅优于传统的多模式集合平均,而且也优于利用全部模式建立的PLS集合预估模型,体现了模式优选过程的重要性。本文基于优选模式的PLS集合预估模型预估结果表明:(1)21世纪各区域温度将持续上升,且冬半年升温速率总体大于夏半年,北方地区升温速率总体高于南方地区;RCP 4.5排放情景下温度上升先快后慢,转折点出现在21世纪中期,RCP 8.5排放情景下,呈持续增加趋势,至21世纪末的升温幅度约为RCP 4.5情景的2倍。(2)21世纪各区降水变化均呈显著增加趋势,并表现出高排放情景大于低排放情景,少雨区大于多雨区的特征,但是降水增加过程伴有明显的年代际波动。对比发现,传统的等权重集合平均全部模式(EMC)方法预估的中国夏季变暖速率高于冬季,且降水基本呈线性增加,有悖于全球变暖的基本特征及中国降水具有鲜明的年代际变化特征的基本认识。因而,本文预估的温度和降水变化特征均更符合中国气候变化的基本规律。

Projection of future climate change scenarios provides the scientific basis for addressing climate change and for proposing strategies of adapting climate change. This study used the simulation data of 30 climate models, which were evolved in the Coupled Model Intercomparison Project Phase 5（CMIP5）. Through evaluating the performance of each model on simulating the historical climate change, the preferred climate models were selected. Then,using the outputs of preferred climate models as independent variables and using ground measurements as dependent variables, the partial least squares regression（PLS） models were constructed for temperature and precipitation, respectively, of each region of China. By analyzing the ensemble predictions of regional temperature and precipitation changes, we found that the PLS ensemble mean of preferred climate models is closer to the ground measurements than the PLS ensemble mean of all of the climate models and the traditionally arithmetic average-based ensemble mean. The PLS ensemble projections of preferred climate model showed that climate warming would generally continue during the 21 st century, which would be stronger in the cold half-year and in the northern regions than that in the warm halfyear and in the southern regions. Under the scenario of RCP 4.5, the climate warming would be stronger in the first half of the 21 st century and weaker in the second half. Under the scenario of RCP 8.5, the climate warming would keep nearly constant rate and, by the end of 21 st century, the temperature would rise by two folds of that under the scenario of RCP 4.5. The increasing trend of precipitation would be stronger under the scenario of RCP 8.5 than that under the scenario of RCP 4.5 and would be stronger in the dry regions than that in the rainy regions with decadal oscillations. Finally, the equal weighting ensemble projections of all of the climate models exhibit that climate warming would be stronger in summer than in winter and that precipitation would increase linearly without decadal oscillations. These findings are opposite to the primary characters of climate changes that climate warming is stronger in winter than in summer and precipitation has strong inter-decadal variability. Thereby, the PSLbased ensemble mean of preferred climate model may provide reasonable projections of future temperature and precipitation changes.