How Does Global Warming Accelerate the Hydrological Cycle in the East Asian Monsoon Region? Atmospheric- and Terrestrial Moisture Pathways Analysis in a Regional Earth System Model

全球变暖被认为会导致全球水文循环的加速。因此，在区域范围内，这可能会改变天气状况，并可能增加水文气象极端事件的数量。在东亚季风区，已经观察到了这种变化，预计这种变化将加剧，这是对区域经济的潜在威胁。此外，该区域的水资源受到人为活动的严重影响，这进一步改变了区域水文循环。然而，将全球变暖和人为活动与东亚季风环流变化、区域水循环加速和极端事件增加联系起来的详细机制尚不完全清楚。传统的方法研究水分停留时间，从而水循环的速度通常受到陆地/次表层与大气之间耦合的粗略假设的限制。一方面，气候模型通常忽略了陆地的横向水流。另一方面，复杂的陆面模型不考虑陆地-大气反馈，因为大气状态是固定的强迫输入。在过去的几年里，在区域气候模型中制定了蒸发标记方法，以调查地表蒸发的水在大气中的去向，直到它沉淀。特别是，最近引入了一种年龄加权的蒸发标记算法，并将其应用于诊断水文循环的大气分支的速度。这一方法现在将扩展到整个区域水文循环：我们将首先加强一个完全耦合的区域大气-水文模型系统(WRF-HMS，即区域地球系统模型)，考虑到人类活动对水资源的影响。其次，我们将开发一种新的方法来联合评估这个增强的区域地球系统模式中的大气和土壤水分路径，该方法基于年龄加权的蒸发和降水标记算法。这使得可以推导出停留时间，从而得出关于水循环的速度和潜在加速的结论。第三，在东亚季风区的情况下，我们将描述当地球系统模式中增加的对陆地侧向水流动的描述以及对水资源管理的描述改变大气和土壤水分路径和停留时间时的大气情况。最后，将新发展的方法应用于长期区域气候模拟和定义的区域气候控制点，将为东亚季风区水循环加速的机制提供一个新的视角。这也使我们能够估计水管理的效果。

Global warming is assumed to cause a global acceleration of the hydrological cycle. Accordingly, at the regional scale, this may modify weather regimes and likely increase the number of hydrometeorological extreme events. In the case of the East Asian monsoon region, such changes have already been observed and are expected to intensify, which is a potential threat for the regional economy. Moreover, water resources in the region are heavily affected by anthropogenic activity, which further modifies the regional hydrological cycle. However, the detailed mechanism linking the global warming and anthropogenic activities to changes in the East Asian monsoonal circulation, a regional acceleration of the hydrological cycle and an increase of extreme events is not fully understood yet.Traditional methods to investigate moisture residence times and thereby the speed of the hydrological cycle are generally limited by crude assumptions in the coupling between the land surface/subsurface and the atmosphere. On the one hand, climate models usually neglect lateral terrestrial water flows. On the other hand, sophisticated land surface models do not account for land-atmosphere feedbacks, as the state of the atmosphere is a fixed forcing input. In the last years, evaporation-tagging methods have been elaborated within regional climate models in order to investigate the fate of surface evaporated water in the atmosphere until it precipitates. In particular, an age-weighted evaporation-tagging algorithm has recently been introduced and applied for diagnosing the speed of the atmospheric branch of the hydrological cycle. This approach will now be extended to the full regional hydrological cycle:We will first enhance a fully coupled regional atmosphere-hydrology model system (WRF-HMS, i.e. a regional Earth System Model) with the effect of anthropogenic activities on water resources. Secondly, we will develop a new method to evaluate jointly the atmospheric and soil moisture pathways in this enhanced regional Earth System Model, based on an age-weighted evaporation- and precipitation-tagging algorithm. This allows the derivation of residence times and thereby conclusions on the speed and potential acceleration of the hydrological cycle. Thirdly, we will characterize the atmospheric situations when the additional description of lateral terrestrial water flows in the Earth System Model, as well as the description of water resource management, alters the atmospheric and soil moisture pathways and residence times in the case of the East Asian monsoon region. Finally, applying the newly developed methods to long term regional climate simulations and defined RCPs, we will provide a new perspective on the mechanism governing the acceleration of the hydrological cycle in the East Asian monsoon region. This also allows us to estimate the effect of water management.