Guo et al. (2025) A new precipitation index for summer precipitation in eastern China

Identification

• Journal: Climate Dynamics
• Year: 2025
• Date: 2025-11-20
• Authors: Jingyan Guo, Wenping He, Shuping Li, Siyi Wang
• DOI: 10.1007/s00382-025-07960-w

Research Groups

• School of Atmospheric Sciences, Sun Yat-Sen University, Zhuhai, China
• College of Hydraulic Science and Engineering, Yangzhou University, Yangzhou, China

Short Summary

This study develops a novel Precipitation Index (PI) for summer precipitation in eastern China, specifically designed to capture the coordinated variability between North and South China. The PI demonstrates superior performance over existing indices in representing synchronous precipitation anomalies and reveals the underlying atmospheric dynamic and thermodynamic mechanisms driving this coherence.

Objective

• To construct a novel Precipitation Index (PI) for summer precipitation in eastern China that effectively characterizes the joint anomalies and coherent variations between North China (NC) and South China (SC).
• To quantitatively assess the spatial representativeness and robustness of the PI.
• To investigate the atmospheric circulation patterns and key dynamic and thermodynamic mechanisms associated with high and low PI values.

Study Configuration

• Spatial Scale: Eastern China, focusing on North China (NC: 34°–42°N, 110°–120°E), South China (SC: 20°–28°N, 105°–120°E), and Central China (CC: 28°–35°N, 105°–120°E) for comparison. Atmospheric diagnostics cover East Asia.
• Temporal Scale: Summer season (June–July–August) over the period 1979–2021 (43 years).

Methodology and Data

• Models used:
  • Empirical Orthogonal Function (EOF) analysis for identifying spatial modes of precipitation.
  • Pearson correlation coefficient for evaluating linear relationships.
  • Composite analysis for investigating atmospheric responses.
  • Multivariate linear regression models for validating predictive capability.
• Data sources:
  • Daily precipitation observations from 1905 meteorological stations across China (1979–2021), provided by the China Meteorological Administration.
  • Fifth-generation ECMWF reanalysis dataset (ERA5) for daily mean specific humidity, latent heat (LH), sensible heat (SH), horizontal wind, 500-hPa vertical velocity (ω), atmospheric precipitable water (APW), 2-meter dewpoint temperature (d2m), and 2-meter temperature (T2m) (0.25° × 0.25° spatial resolution).
  • Daily mean outgoing longwave radiation (OLR) from the National Oceanic and Atmospheric Administration (NOAA) (2.5° horizontal resolution).
  • Fifth-generation extended reconstruction sea surface temperature dataset (ERSSTv5) from NOAA.

Main Results

• The first EOF mode of summer precipitation in eastern China accounts for 24.41% of the total variance, exhibiting a tripole pattern with in-phase anomalies in NC and SC, and out-of-phase anomalies in CC.
• The newly constructed Precipitation Index (PI) shows significantly higher correlations with regional precipitation in NC and SC compared to existing indices (PC1, MI, AI), and a higher probability of capturing same-signed anomalies in these regions.
• PI's spatial correlation pattern with precipitation displays significant positive correlations in NC and SC, and negative in CC, consistent with the leading EOF mode.
• PI exhibits an upward trend of 2.56 × 10⁻² (10a)⁻¹ from 1979 to 2021, aligning with increasing precipitation trends in NC and SC.
• High PI years are characterized by enhanced convection (negative ω anomalies up to -0.014 Pa s⁻¹, negative OLR anomalies up to -4.89 W m⁻²) and abundant moisture supply (positive d2m anomalies up to 0.484 K, positive APW anomalies up to 1.78 kg m⁻²) in NC and SC. This is supported by an anomalous anticyclonic circulation at 850-hPa over the western Pacific, driving northward moisture transport.
• Low PI years show reversed patterns, with suppressed convection (positive ω, positive OLR), reduced moisture, and an anomalous cyclonic circulation disrupting moisture inflow.
• Surface heat fluxes (LH, SH) also align with PI variability, showing positive anomalies in SC during strong PI years (LH: 1.094 J m⁻², SH: 1.756 J m⁻²) and negative in CC.
• Incorporating PI as a predictor significantly enhances the accuracy of seasonal precipitation forecasts for NC and SC, outperforming models based on other indices.

Contributions

• Introduces a novel Precipitation Index (PI) specifically designed to capture the coherent (in-phase) variability of summer precipitation in North China and South China, addressing a limitation of existing indices.
• Quantitatively demonstrates the superior performance and robustness of the PI in representing synchronous precipitation anomalies across NC and SC.
• Provides a comprehensive diagnostic analysis of the dynamic and thermodynamic coupling mechanisms (vertical motion, moisture transport, thermal conditions, and wind patterns) that drive the observed synchronous precipitation anomalies.
• Validates the practical utility of the PI for seasonal precipitation prediction, showing significant improvements in forecast accuracy for NC and SC.
• Offers a new and valuable perspective for understanding and predicting complex precipitation variability in eastern China, particularly the coupled behavior between its northern and southern regions.

Funding

• National Natural Science Foundation of China (Grant Nos. 42175067, 42375059, 41775092, and 41975086).

Citation

@article{Guo2025new,
  author = {Guo, Jingyan and He, Wenping and Li, Shuping and Wang, Siyi},
  title = {A new precipitation index for summer precipitation in eastern China},
  journal = {Climate Dynamics},
  year = {2025},
  doi = {10.1007/s00382-025-07960-w},
  url = {https://doi.org/10.1007/s00382-025-07960-w}
}