State-of-the-art climate change projections of the CMIP5 simulations suggest a fairly complex pattern of global precipitation changes, with regions of reduced and enhanced precipitation. Conceptual understanding of these projected precipitation changes is difficult if only based on coupled general circulation model (CGCM) simulations, due to the complexity of these models. In this study we describe a simple deconstruction of the ensemble mean CMIP5 projections based on sensitivity simulations with the globally resolved energy balance (GREB) model. In a series of sensitivity experiments we force the GREB model with four different CMIP5 ensemble mean changes in: surface temperature, evaporation and the vertical atmospheric velocities mean and its standard deviation. The resulting response in the precipitation of the GREB model is very close to the CMIP5 ensemble mean response, suggesting that the precipitation changes can be well represented by a linear combination of these four forcings. The results further provide good insights into the drivers of precipitation change. The GREB model suggests that not one forcing alone can be seen as the main driver, but only the combination of all four changes results in the complex response pattern. However, the dominant forcings are the changes in the large-scale circulation, rather than the pure thermodynamic warming effect. Here, it is interesting to note that changes in high-frequency atmospheric variability of vertical air motion (weather), that are partly independent of the changes in the mean circulation, have a control on the pattern of the time-mean global precipitation changes. The approach presented here provides a powerful basis on which the hydrological cycles of CGCM simulations can be analysed.

CMIP5模拟的最新气候变化预测表明，全球降水变化的模式相当复杂，且降水量减少和增加。如果仅基于耦合总循环模型（CGCM）模拟，则很难从概念上理解这些预计的降水变化，因为这些模型非常复杂。在这项研究中，我们描述了基于均值能量平衡（GREB）模型的灵敏度模拟对集合平均CMIP5投影的简单解构。在一系列的敏感性实验中，我们用四个不同的CMIP5集合平均值的平均值来强制GREB模型：表面温度，蒸发量和垂直大气速度的平均值及其标准偏差。GREB模型降水中的最终响应非常接近CMIP5整体平均响应，这表明降水变化可以通过这四个强迫的线性组合很好地表示。结果进一步提供了对降水变化驱动力的深刻见解。GREB模型表明，不能仅将一个强迫作为主要驱动因素，而只有所有四个变化的组合才能导致复杂的响应模式。但是，主要的强迫是大规模循环的变化，而不是纯粹的热力学增温作用。在这里，有趣的是，垂直空气运动（天气）的高频大气变化的变化部分与平均循环的变化无关，控制时间平均全球降水量变化的模式。此处介绍的方法为分析CGCM模拟的水文循环提供了有力的基础。