Model-simulated hydroclimate variability of the East Asian Summer Monsoon across different climates: insights from a moisture source perspective

Here we study the sensitivity of monsoon season precipitation in the Yangtse River Valley (YRV, 110-122° E and 27-33° N, East China) to climatic boundary conditions from the last glacial maximum (LGM), pre-industrial conditions, and with the RCP6.0 emission scenario. Using a quantitative Lagrangian moisture source diagnostic, we interpret changes in precipitation amount and seasonality in terms of processes at the source regions that contribute to YRV precipitation. Thereby, we gain insight into inﬂuential processes and characteristics related to precipitation variability, and the sensitivity of the summer 5 monsoon hydroclimate in East Asia to boundary condition changes in models. Comparing 10-year time slices similar to present-day conditions from the NorESM1-M and CAM5.1 models to ERA Interim reanalysis data reveals overall very similar moisture source regions, albeit with a tendency to more local precipitation origin in the climate models. Also across different climate forcings, the general characteristics of the moisture sources and moisture transport to the YRV are relatively stable, both concerning the location of source regions, their magnitudes, and the relative contributions of moisture from land and ocean 10 areas. Differences in moisture source conditions are larger between the different climate models, than between different climatic boundary conditions using the same model. Overall, these ﬁndings imply that the moisture source regions, and thus the general processes of precipitation in the YRV could remain relatively stable across different climatic periods. However, the results may also indicate that current climate models underestimate the potential for non-linear responses to changing boundary conditions. The plausibility of moisture source changes simulated by the different models could in be evaluated in the future 15 method. Here we use the Lagrangian moisture source diagnostic of Sodemann et al. (2008) to obtain the moisture sources of the YRV as a core region of the East Asian monsoon system using simulations from two climate models for different climatic periods. This is the ﬁrst time this moisture diagnostic is used with free-running model simulations without inﬂuences from 80 data assimilation associated with reanalysis data. First, we assess how different climate models transport moisture to the YRV during the monsoon season in a present-day climate, using results obtained previously from reanalyses as a reference (Fremme and Sodemann, 2019). From simulations with different climatic boundary conditions, we then identify how models represent hydroclimate variability during the simulated East Asian Summer monsoon to orbital forcing and ice-sheet topography from analyzing time slices of an uncoupled simulation of the last glacial maximum (LGM). Furthermore, the changes of the monsoon 85 system in a future climate scenario with increased atmospheric CO 2 concentrations are assessed in a coupled model run for a time slice near end of the 21st century. Based on our ﬁndings, we then discuss in particular the role of land-surface processes, and conclude with remarks on the potential of a moisture source perspective for understanding hydroclimate variability, and for interpreting paleoclimate records from the East-Asian monsoon region.