East Asian Spring Precipitation and its Dry Trend revealed by CMIP6 High-Resolution Coupled Models

The persistent spring precipitation over East Asia, with a notable drying trend in recent decades, poses substantial impacts on the regional hydrological cycle and socio-economy. This study investigates the climatology and long-term trend of East Asian spring precipitation during 1980-2014 simulated from CMIP6 HighResMIP coupled models, focusing on the role of model horizontal resolution. Our results show that high-resolution models outperform their low-resolution counterparts in simulating the spatial pattern and intensity of East Asian spring mean precipitation, owing to improved representations of low-level winds and moisture transport. However, many high-resolution models in HighResMIP fail to reproduce the long-term variation of East Asian spring precipitation and associated remote influencing factors (e.g., tropical Pacific and North Atlantic sea surface temperature) while only two models (FGOALS-f3-H and EC-Earth3P-HR) show improved performance for this unique climate phenomenon. Particularly, the high-resolution FGOALS-f3-H model exhibits the best skill in simulating this regional climatic change, increasing a regional mean drying trend from -0.10 in its low-resolution version to -0.33 mm day^-1 decade^-1 (observed: -0.43). This remarkable improvement in FGOALS-f3-H stems from more realistic representations of both the weakening Western North Pacific Anticyclone and strengthening Mongolia High, which are key regional circulation drivers of the East Asian spring drying trend, as well as its improved simulation of the weakening vertical velocity over East Asia. By contrast, five out of all seven high-resolution models show degraded performance in reproducing this precipitation trend, even showing amplified simulation biases in precipitation trend and improper relationships with remote and regional influencing factors relative to their low-resolution counterparts. This study suggests that the simultaneous improvement of horizontal resolution and physical parameterizations governing precipitation-related interannual variability in climate models is critical for simulating East Asian climatic change.

Keywords: East Asia, spring precipitation, high-resolution models, CMIP6