High Mountain Asia (HMA), the source region of major Asian rivers, plays a vital role in sustaining downstream water and ecosystem security. Over the past 50 years, summer precipitation in HMA has exhibited a dipole pattern—drying in the south and moistening in the north. While global climate models are widely used to explore the mechanisms and projections of these changes, their performance remains limited by the region’s complex terrain and unique climate conditions.  A key question thus arises: Can enhanced model resolution yield greater fidelity in simulating HMA precipitation?

A new study published on October 15 in Journal of Climate addresses this issue, revealing the added value and physical mechanisms of increased horizontal resolution in simulating HMA long-term precipitation trends. The work was led by Ph.D. student Li Lan from the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences, and the University of Chinese Academy of Sciences (UCAS).

Using six pairs of CMIP6 models with different horizontal resolutions, the team analyzed how higher resolution improves the simulation of long-term summer precipitation trends (1951–2014) and explored the physical mechanisms driving this improvement.

“The high-resolution models capture observed precipitation trends much more accurately than their low-resolution counterparts—especially over the southern margin of the HMA and nearby regions—reducing the wet bias by roughly 65%,” said Li Lan, the study's lead author.

What drives this improvement? “The enhanced performance of high-resolution models primarily stems from remote forcing associated with Indian Ocean SST warming, rather than local orographic effects,” explained Professor Zhou Tianjun, the study's corresponding author.

In-depth analyses of moisture budget and moist static energy budget reveal that the high-resolution models can better capture a warm sea surface temperature (SST) pattern over the central tropical Indian Ocean. This SST anomaly suppresses precipitation over the South China Sea and the Maritime Continent, which in turn triggers a Rossby wave response that generates an anomalous anticyclonic circulation over the northern Bay of Bengal. The resulting anticyclonic flow transports dry air into the southern HMA, suppressing local convection and alleviating excessive precipitation in the region.

 Linear trends of summer precipitation during 1951–2014 in High Mountain Asia (units: mm·month⁻¹·decade⁻¹). (a) Observed trends based on GPCC data. (b) Trend differences between low-resolution models and GPCC. (c) Same as (b), but for differences between high- and low-resolution models.

This study demonstrates that, under the same physical configuration, climate models with higher horizontal resolution more accurately reproduce precipitation trends over High Mountain Asia. The researchers therefore recommend using high-resolution models when studying water cycle changes in regions with complex terrain. They hope these findings will offer valuable insights for improving the next generation of climate models.

Reference: Li, L., T. Zhou, J. Jiang, X. Chen, S. Hu, Z. Ren, and L. He, 2025: High-Resolution CMIP6 Models Better Capture Southern High Mountain Asia Precipitation Trends. J. Climate, 38, 6593–6604, https://doi.org/10.1175/JCLI-D-25-0099.1.