Ellis et al. (2025) Distinguishing Precipitation by Process as a Prerequisite for Understanding Hydroclimate Change: An Example from the Southeastern Lake-Effect Region of the Great Lakes Basin

Identification

• Journal: Climatic Change
• Year: 2025
• Date: 2025-12-01
• Authors: Andrew W. Ellis, Christopher Mays
• DOI: 10.1007/s10584-025-04071-7

Research Groups

• Department of Geography, Virginia Tech, Blacksburg, VA, USA

Short Summary

This study reveals that analyzing total cool-season precipitation in the southeastern Great Lakes region masks opposing trends in synoptic-scale and mesoscale lake-effect precipitation over a 47-year period, demonstrating that process-based stratification is essential for accurately understanding hydroclimate change.

Objective

• To demonstrate that distinguishing precipitation by process (synoptic-scale vs. lake-effect) is crucial for understanding hydroclimate change, as aggregated total precipitation trends can mask significant, opposing changes in these distinct mechanisms.

Study Configuration

• Spatial Scale: Southeastern lake-effect region of the Great Lakes Basin, specifically to the southeast of Lakes Erie and Ontario, North America. Data from 43 stations were analyzed.
• Temporal Scale: A 47-year period from November 1968 to April 2015, focusing on the cool season (November–April).

Methodology and Data

• Models used: Non-parametric statistical methods were employed for trend analysis: Sen’s slope estimator and Mann-Kendall trend test. Precipitation volatility was quantified using the Gini coefficient (GC) and Lorenz Asymmetry coefficient (LAC).
• Data sources:
  • Lake-effect calendar: A hybrid daily calendar for the eastern Great Lakes region (Ellis and Suriano, 2022), combining air mass modification data (Ellis et al., 2021) and synoptic weather typing (Suriano and Leathers, 2017).
  • Daily liquid precipitation and daily maximum/minimum air temperature data: Global Historical Climate Network-Daily (GHCN-D) dataset from the United States National Centers for Environmental Information (NCEI) for 43 stations.

Main Results

• Total cool-season precipitation (mean 453.4 mm) and frequency (mean 84.5 days) showed no statistically significant trend over the 47-year period. Mean regional daily air temperature (0.65 °C) also exhibited no significant trend.
• Lake-effect precipitation, accounting for 27% of total precipitation (mean 124.2 mm), significantly decreased at a rate of 6.85 mm per decade (p=0.03).
• Lake-effect precipitation frequency significantly decreased at a rate of 1.30 days per decade (p=0.03).
• Synoptic precipitation (mean 329.3 mm) significantly increased at a rate of 11.92 mm per decade (p=0.05).
• The percentage contribution of lake-effect precipitation to total precipitation and frequency significantly decreased, while that of synoptic precipitation significantly increased.
• Synoptic precipitation exhibited increased spatial volatility, with statistically significant positive trends in the standard deviation of precipitation frequency and intensity across the 43 stations.
• Synoptic precipitation also showed increased temporal volatility, with significant increases in the mean regional frequency of light (0.71 days per decade, p=0.03), heavy (0.23 days per decade, p=0.03), and very heavy (0.09 days per decade, p<0.01) daily precipitation days.
• Lake-effect precipitation showed decreased temporal volatility, indicated by a significant decline in the Gini coefficient (GC) (more equitable distribution) and the Lorenz Asymmetry coefficient (LAC) (inequity increasingly due to smaller events).
• Conversely, the GC for synoptic precipitation significantly increased, indicating a less equitable distribution and increased volatility.

Contributions

• Demonstrates the critical importance of distinguishing precipitation by its underlying atmospheric process (synoptic-scale vs. mesoscale lake-effect) to accurately identify and understand hydroclimate change, especially in mid-latitude regions with diverse precipitation mechanisms.
• Reveals that an apparent lack of trend in aggregated total cool-season precipitation can mask significant, opposing trends in its constituent processes, providing a crucial caveat for hydroclimatic analyses.
• Provides novel insights into the contrasting responses of different precipitation mechanisms to broader climate changes, showing increased amount and volatility for synoptic precipitation versus decreased amount, frequency, and volatility for lake-effect precipitation.
• Applies the Gini coefficient (GC) and Lorenz Asymmetry coefficient (LAC) to analyze precipitation intensity variability within a lake-effect region, contributing to a knowledge gap in this specific context.

Funding

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Citation

@article{Ellis2025Distinguishing,
  author = {Ellis, Andrew W. and Mays, Christopher},
  title = {Distinguishing Precipitation by Process as a Prerequisite for Understanding Hydroclimate Change: An Example from the Southeastern Lake-Effect Region of the Great Lakes Basin},
  journal = {Climatic Change},
  year = {2025},
  doi = {10.1007/s10584-025-04071-7},
  url = {https://doi.org/10.1007/s10584-025-04071-7}
}