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

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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.