Exploring changes of precipitation extremes under climate change through global variable-resolution modeling

Understanding the responses of precipitation extremes to global climate change remains limited owing to their poor representations in models and complicated interactions with multi-scale systems.Here we take the record-breaking precipitation over China in 2021 as an example,and study its changes under three different climate scenarios through a developed pseudo-global-warming(PGW)experimental framework with 60-3 km variable-resolution global ensemble modeling.Compared to the present climate,the precipitation extreme under a warmer(cooler)climate increased(decreased)in intensity,coverage,and total amount at a range of 24.3%-37.8%(18.7%-56.1%).With the help of the proposed PGW experimental framework,we further reveal the impacts of the multi-scale system interactions in climate change on the precipitation extreme.Under the warmer climate,large-scale water vapor transport converged from double typhoons and the subtropical high marched into central China,enhancing the convective energy and instability on the leading edge of the transport belt.As a result,the mesoscale convective system(Mcs)that directly contributed to the precipitation extreme became stronger than that in the present climate.On the contrary,the cooler climate displayed opposite changing characteristics relative to the warmer climate,ranging from the large-scale systems to local environments and to the Mcs.In summary,our study provides a promising approach to scientifically assess the response of precipitation extremes to climate change,making it feasible to perform ensemble simulations while investigating the multi-scale system interactions over the globe.

Differences in the Rainfall Characteristics between Mount Tai and Its Surrounding Areas

As a typical small-scale, isolated topography, Mount Tai exhibits great differences in precipitation characteristics from the surrounding areas. It was found that the amount of rainfall occurring over Mount Tai is significantly larger than what is observed in the surrounding areas. Based on hourly rain gauge records for the warm season(May to September) of 1996–2015, differences between Mount Tai and its surrounding areas were further revealed in terms of rainfall diurnal variation, spatial scale, and evolution process. The diurnal variation of the enhancement on rainfall amount exhibit "dual peaks" occurring in the early morning and afternoon, and the dual peaks are mainly attributable to rainfall frequency. The diurnal phase of the rainfall amount in the surrounding areas lags 1 h behind that over Mount Tai. Regarding differences in rainfall spatial scale, compared to those of surrounding areas, precipitation over Mount Tai is characterized by a smaller coverage, especially in the early morning. Mount Tai also tends to have a kind of unique, small-scale rainfall in the afternoon and at night. Based on statistical analysis of precipitation events,differences in rainfall evolution process were identified as well. Rainfall over Mount Tai often starts earlier in the afternoon and ends later at night than it does in the surrounding areas. Furthermore, nocturnal rainfall events over Mount Tai are prone to peaking over a shorter period and enduring for a longer period after reaching their maximum intensity, compared with nocturnal rainfall events occurring in the surrounding areas. Rainfall events over Mount Tai always last longer, especially those occurring in the early morning. In general, Mount Tai has a large enhancement effect on rainfall.

Obtaining More Information about Precipitation Biases over East Asia from Hourly-Scale Evaluation of Model Simulation

The hourly summer precipitation simulations over East Asia by the Chinese Academy of Meteorological Science Climate System Model(CAMS-CSM)high-resolution Atmospheric Model Intercomparison Project(AMIP)runs(T255,~50 km)were evaluated based on the merged hourly precipitation product released by the China Meteorological Administration(CMA).The results show that the simulation biases are closely related to the topography,with the precipitation amount and frequency overestimated(underestimated),and duration of precipitation events being longer(shorter),over the western high-altitude(eastern plain)regions of China.Six regions with large discrepancies were further analyzed.In terms of the frequency-intensity structure,the overestimation of precipitation frequency is mainly due to the excessive simulated weak precipitation over the four regions with positive biases:the southern edge of the Tibetan Plateau(STP),the northeastern edge of the Tibetan Plateau(NETP),the eastern periphery of the Tibetan Plateau(EPTP),and the mountainous area of North China(NCM);while the underestimation of frequency is mainly due to the insufficient precipitation with moderate intensity over the two regions with negative biases:lower reaches of the Yangtze River(LYR)and the South China coast(SCC).Based on the duration-diurnal structure analysis,two kinds of precipitation events with different natures can be distinguished.The long-duration night to early morning precipitation events have a significant contribution to the precipitation amount biases for all the six key regions,and this kind of precipitation mainly affects the precipitation diurnal variation over the mountainous areas or steep terrain.Although the short-duration afternoon precipitation events only have a greater contribution to the precipitation amount biases over the SCC region,this kind of precipitation affects the diurnal variation over the NCM region and the two key regions with negative biases.Such a detailed hourly-scale evaluation is helpful for enriching the understanding of simulation biases and to further improve model performance.