High Mountain Asia (HMA), the source of Asia's major rivers and a critical contributor to downstream water security and ecosystem health, has seen a dipole pattern in summer precipitation over the past 50 years: drying in the south and increased moisture in the north. While global climate models are the primary tools for studying the drivers and projections of these changes, their reliability is hampered by the region's complex terrain and unique climatic conditions. This raises a question: Can boosting model resolution enhance the accuracy of HMA precipitation simulations?

A team of researchers led by the Institute of Atmospheric Physics of the Chinese Academy of Sciences and the University of Chinese Academy of Sciences has now answered that question. Their study, recently published in Journal of Climate, quantifies the added value of higher horizontal resolution in simulating long-term HMA precipitation trends and identifies the underlying physical mechanisms.

In this study, the team analyzed six pairs of CMIP6 models with different horizontal resolutions to evaluate how resolution impacts the simulation of summer precipitation trends between 1951 and 2014. They also investigated the physical processes driving any improvements in accuracy.

The results showed that high-resolution models outperformed their low-resolution counterparts in capturing observed precipitation trends, particularly across the southern margin of HMA and adjacent regions. Specifically, the high-resolution simulations reduced the wet bias by approximately 65%, the researchers noted.

"The performance of high-resolution models does not come from local topographic effects, but rather from their ability to capture remote forcing linked to warming sea surface temperatures (SSTs) in the Indian Ocean," explained Prof. ZHOU Tianjun, the study's corresponding author.

In-depth analyses of moisture budgets and moist static energy budgets revealed that the high-resolution models can better capture a warm SST pattern over the central tropical Indian Ocean. This SST anomaly suppresses precipitation over the South China Sea and the Maritime Continent, triggering a Rossby wave response that creates an anomalous anticyclonic circulation over the northern Bay of Bengal. This circulation then transports dry air into southern HMA, damping local convection and reducing the excessive rainfall in the region.

The study confirms that, even with identical physical frameworks, higher horizontal resolution improves the accuracy of HMA precipitation trend simulations.

 Linear trends of summer precipitation during 1951–2014 in HMA (units: mm·month⁻¹·decade⁻¹). (Image by Prof. ZHOU Tianjun's team)