Projected Responses of Extreme Precipitation and Atmospheric Radiative Energy (PREPARE)

预计降雨及其强度的增加和干旱地区的覆盖范围将对社会、农业和健康造成不利影响。一组新出现的证据表明，气候模型可能低估了当前全球水循环的变化。查明和解决大气水循环对气候变暖的模拟响应与观测响应之间存在差异的原因是至关重要的，也是及时的。目前的提案将重要的研究领域和具有独特专业知识的合作者聚集在一起，试图检验以下假设：(I)卫星数据的限制是否妨碍了我们监测全球水循环变化的能力？(2)目前地球上与气溶胶有关的能量平衡的变化是否会影响水文循环的趋势？(3)对未来降雨量及其极端变化的预测有何影响？要回答这些问题，就需要了解降雨变化的根本原因。来自复杂气候模型的证据和来自各种来源的观测表明，大气湿度的强劲增加与基本物理考虑预期的升温速度大致相同(每K升温约7%)。不断上升的湿度加剧了最强降雨事件的发生。这并不是故事的全部：全球降水与地球大气能量收支有着内在的联系。随着地球变暖，大气辐射冷却的上升相对缓慢，只能通过每K约1-3%的降水支持潜热的适度上升，远远慢于暴雨的上升。这导致远离对流区域的降雨量减少。虽然气候模型和卫星观测都表明，干旱地区正在变得更加干燥，潮湿地区正在变得更加潮湿，但进一步的比较表明，这些模型低估了这种反应。为了理解模型和数据之间存在重大差异的原因，我们汇集了地球能源平衡和全球水循环方面的重要专业知识领域。这三种主要方法是：(1)监测、(2)相互比较和(3)了解和预测水文循环的变化。这可以通过利用卫星和地面测量降水、蒸发和地球辐射能量平衡的独特组合来实现。现有和新的卫星数据集的相互比较将有助于改进对降水和蒸发等关键变量变化的监测。将模型和观测数据中能量和水平衡的水文和辐射部分结合起来，将使人们能够更好地了解所涉及的物理过程，并改进对地表辐射收支变化的估计。精心设计的模型实验将探索气溶胶变化通过辐射强迫对水文循环的影响。这些结果对于改进对水文循环变化对社会和生态系统未来影响的估计至关重要。

Projected increases in rainfall and its intensity and the coverage of regions experiencing drought will lead to adverse impacts on societies, agriculture and health. An emerging body of evidence indicates that climate models may underestimate the current changes in the global water cycle. It is crucial and timely that the causes of discrepancies between simulated and observed responses of the atmospheric hydrological cycle to warming are identified and addressed. Bringing together important lines of research and collaborators with unique expertise the current proposal seeks to test the following hypotheses: (i) Are limitations of the satellite data hampering our ability to monitor changes in the global water cycle? (ii) Are present day changes in the Earth's energy balance relating to aerosol influencing trends in the hydrological cycle? (iii) What are the implications for projections of future changes in rainfall and its extremes? To answer these questions, an appreciation for the root causes of changes in rainfall is required. Evidence from sophisticated climate models and observations from a variety of sources point to robust increases in atmospheric moisture with warming at about the rate expected from basic physical considerations (around 7% per K warming). Rising moisture fuels intensification of the heaviest rainfall events. This is not the full story: global precipitation is intrinsically linked to Earth's atmospheric energy budget. The relatively slow rises in atmospheric radiative cooling, as the planet warms, can only support modest rises in latent heating through precipitation of around 1-3% per K, much slower than the rises in heavy rainfall. This leads to a reduction in rainfall away from convective regimes. While both climate models and satellite observations indicate that the dry regions are becoming drier and the wet regions wetter, further comparison suggests that the models underestimate this response. To understand the reasons for the important discrepancy between models and data, we bring together important areas of expertise in the Earth's energy balance and the Global water cycle. The three main approaches are to (i) monitor, (ii) inter-compare and (iii) understand and predict changes in the hydrological cycle. These can be achieved by employing a unique combination of satellite and surface-based measurements of precipitation, evaporation and the Earth's radiative energy balance. Inter-comparison of existing and new satellite datasets will allow improved monitoring of changes in key variables such as precipitation and evaporation. Combining the hydrological and radiative components of the energy and water balance in models and observational data will enable a better understanding of the physical processes involved and improve estimates of changes in the surface radiation budget. Carefully constructed model experiments will explore the impact of changes in aerosol on the hydrological cycle through radiative forcings. The results will be paramount in improving estimates of future impacts from changes in the hydrological cycle on societies and ecosystems.