Simulation And Projection Of Precipitaion Over Tibetan Plasteau By CMIP6 Models

The Tibetan Plateau is one of the sensitive regions to global climate change.It is necessary to accurately simulate and reasonably predict the temporal and spatial changes of precipitation.For a long time,it has been a challenge to reproduce the precipitation characteristics over the Tibetan Plateau.With the implementation of the sixth phase of Couple Model Intercomparison Project(CMIP6),the results of the new generation of global climate models have been published.Compared with the CMIP5 models,the process considered in CMIP6 models is more complicated,and the resolution of CMIP6 models is significantly improved.Focus on precipitation over the Tibetan Plateau,this paper evaluated the ability of low(?100km)-,medium(?50km)-and high(?25km)-resolution atmospheric circulation models to simulate hourly precipitation,and analyzed the impact of model resolution on hourly precipitation simulation.Under the circumstance that resolution increase will bring about simulation value-added,the high-resolution global coupled models(?100km)were evaluated for its ability to simulate climatic precipitation and long-term changes of precipitation.Finally,the precipitation changes under different emission scenarios and at different periods in the future were estimated,and the uncertainty of precipitation projection was analyzed and discussed.The main conclusions are as follows:CMIP6 atmospheric circulation models with different resolutions can roughly reproduce the spatial distribution of precipitation amount,frequency and intensity over the Tibetan Plateau,but the models overestimate precipitation amount and frequency,and underestimate precipitation intensity.The areas with large deviations are mainly located in the steep terrain.Improved model resolution reduces the simulation bias and enhances the ability to characterize the correlation between precipitation and terrain elevation.From the perspective of precipitation intensity-frequency distribution,the increase in resolution has not effectively improved the overestimation of weak precipitation,but it has improved the problem of underestimation of the maximum precipitation intensity and the frequency of heavy precipitation.In the simulation of diurnal variation,resolution increase can significantly improve the ability to simulate the precipitation diurnal amplitude,and it can also reproduce the finer spatial distribution characteristics of the precipitation diurnal peaks.However,the simulation of the plateau precipitation peaks is too early,and there is a problem of false precipitation peak in the afternoon.The 100 km global coupled models is consistent with the 100 km atmospheric circulation models in terms of the characteristics of climatic precipitation.The overestimation of precipitation amount and frequency is mainly contributed by daytime precipitation,while the underestimation of precipitation intensity is more affected by nighttime precipitation.Models underestimate the linear increase trend of summer precipitation over the Tibetan Plateau from 1979 to 2014,and overestimates the interannual variability of precipitation.In the observation,the change trend of summer precipitation is mainly dominated by nighttime precipitation,while in models,the change of daytime precipitation is dominated.In the future,the average precipitation of the Tibetan Plateau will increase under different scenarios and at different periods,especially under the SSP5-8.5 scenario and at the end of the 21 st century.The increase in annual precipitation is mainly contributed by daytime precipitation.There is an interdecadal fluctuation in the rate of the Plateau precipitation increase.Under the SSP1-2.6 scenario,the increase rate of precipitation will slow down gradually;under the SSP2-4.5 scenario,the increase rate of precipitation will be first fast and then slow;and under the SSP5-8.5 scenario,the increase rate of precipitation will gradually accelerate.In terms of spatial distribution,precipitation in the western part of the plateau has the strongest increase,and in the southern and eastern parts of the plateau decreases to some extent in the early 21 st century.The sensitivity of precipitation to emission scenarios differs in different periods,which is stronger in the late of the 21 st century than in the early and middle periods.For the uncertainty of precipitation projection,the uncertainty of the model and internal variability both contribute to the uncertainty of the precipitation projection,and the large uncertainty area is located in the western plateau.