Zhang et al. (2026) Quantifying the impacts of increasing light and moderate rainfall on permafrost thermal regimes over the Qinghai-Tibet Plateau: A controlled sensitivity study

Identification

• Journal: Journal of Hydrology
• Year: 2026
• Date: 2026-01-08
• Authors: G. L. Zhang, Cuicui Mu, Y. Zhang, Xuetao Zhu, Yi Zhao, Zhuotong Nan
• DOI: 10.1016/j.jhydrol.2026.134926

Research Groups

• Key Laboratory of Western China’s Environmental Systems (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou, China
• Key Laboratory of Cryospheric Science and Frozen Soil Engineering, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China
• Key Laboratory for Water and Sediment Sciences (Ministry of Education), College of Environmental Sciences and Engineering, Peking University, Beijing, China
• Key Laboratory of Ministry of Education on Virtual Geographic Environment, Nanjing Normal University, Nanjing, China

Short Summary

This study quantifies the impact of increasing summer light and moderate rainfall on permafrost thermal regimes over the Qinghai-Tibet Plateau using a land surface model, finding that both rainfall types induce widespread cooling in the active layer and near-surface permafrost, with light rainfall having a stronger effect, particularly in dry regions.

Objective

• To quantify the effects of summer light and moderate rainfall on permafrost thermal regimes across the Qinghai-Tibet Plateau.
• To analyze the contributions of light and moderate rainfall to summer precipitation totals.
• To evaluate resulting changes in surface energy fluxes, soil moisture, soil temperature, and permafrost indicators.
• To quantify the sensitivity of permafrost thermal metrics to a 10 mm increase in each rainfall category.

Study Configuration

• Spatial Scale: Qinghai-Tibet Plateau (QTP) permafrost regions, simulated at 0.1° spatial resolution.
• Temporal Scale: 100-year simulations for each scenario, with a 3-hourly temporal resolution. Summer (June–August) precipitation was the focus, using 1986–1995 as the reference period.

Methodology and Data

• Models used: A modified Noah Land Surface Model (LSM) adapted for permafrost simulation on the QTP. Enhancements include a thermodynamic roughness scheme, a thermal conductivity scheme for gravel and bedrock, a hydraulic conductivity scheme constrained by ice content, and an 18-layer soil column extended to 15.2 m depth.
• Data sources:
  • Atmospheric forcing: China Meteorological Forcing Dataset (CMFDv1.6, 0.1° resolution, 3-hourly), providing air temperature, pressure, wind speed, humidity, downward shortwave and longwave radiation, and precipitation.
  • Lower boundary condition: Ground temperature at 40 m depth, estimated using a regression model.
  • Initial soil temperature and ice profiles: From the Tanggula permafrost site.
  • Soil texture: 1-km, 18-layer dataset, with bedrock properties updated.
  • Vegetation types: 1:1 million Vegetation Atlas of China.

Main Results

• Summer precipitation on the QTP during 1986–1995 averaged approximately 200 mm, with light rainfall contributing 39.4% and moderate rainfall 40.8% of seasonal totals. Light rainfall prevails in dry regions, while moderate rainfall dominates wetter areas.
• Increases in both light and moderate rainfall enhance latent heat flux while suppressing sensible and ground heat fluxes, leading to a net decrease in subsurface heat input and widespread cooling within the active layer and near-surface permafrost.
• Cooling effects are most pronounced in dry areas and within the upper ~3 m of the soil profile.
• For equivalent precipitation increases, light rainfall produces a stronger cooling response than moderate rainfall.
• An additional 10 mm of summer light rainfall reduces active layer thickness (ALT) by 0.05 m and temperature at the top of permafrost (TTOP) by 0.03 °C across the QTP.
• An additional 10 mm of summer moderate rainfall reduces ALT by 0.04 m and TTOP by 0.02 °C across the QTP.
• In dry regions, a 10 mm increase in light rainfall reduces ALT by 0.07 m and TTOP by 0.04 °C, compared with 0.05 m and 0.03 °C for moderate rainfall. Wet regions show much weaker sensitivity (0.01 m and 0.01 °C reductions for both rainfall types).
• Long-term simulations show declines in ALT and TTOP, accompanied by minor increases in permafrost area.

Contributions

• Provides the first regional-scale quantification of the distinct thermal effects of summer light and moderate rainfall on permafrost thermal regimes over the Qinghai-Tibet Plateau.
• Highlights the critical importance of explicitly accounting for rainfall type, intensity, and spatial variability in permafrost assessments, beyond just total precipitation amount.
• Demonstrates that frequent light rainfall can partially offset permafrost warming in arid alpine environments, presenting a contrasting mechanism to warming effects observed in many high-latitude permafrost systems.
• Offers century-scale simulation results that capture cumulative rainfall-induced hydrothermal impacts, complementing existing site-scale and short-term observational studies.

Funding

• National Natural Science Foundation of China (42201136, U25A20762)
• Key R&D Program of Gansu Province (25YFFA001)
• Program of the State Key Laboratory of Cryospheric Science and Frozen Soil Engineering, CAS (No.CSFSE-KF-2418)
• Start-up Funds for Introduced Talent at Lanzhou University (561120216)

Citation

@article{Zhang2026Quantifying,
  author = {Zhang, G. L. and Mu, Cuicui and Zhang, Y. and Zhu, Xuetao and Zhao, Yi and Nan, Zhuotong},
  title = {Quantifying the impacts of increasing light and moderate rainfall on permafrost thermal regimes over the Qinghai-Tibet Plateau: A controlled sensitivity study},
  journal = {Journal of Hydrology},
  year = {2026},
  doi = {10.1016/j.jhydrol.2026.134926},
  url = {https://doi.org/10.1016/j.jhydrol.2026.134926}
}