Gül et al. (2025) Modified standardized precipitation index for skewed hydro-meteorological data

Identification

• Journal: Physics and Chemistry of the Earth Parts A/B/C
• Year: 2025
• Date: 2025-12-04
• Authors: Murat Gül, Yavuz Selim Güçlü
• DOI: 10.1016/j.pce.2025.104234

Research Groups

Istanbul Technical University, Civil Engineering, Hydraulic Division, Istanbul, Türkiye

Short Summary

This study introduces the Modified Standardized Precipitation Index (M-SPI), which uses the median for standardization, to improve drought and wetness representation in skewed precipitation data compared to the traditional mean-based Standardized Precipitation Index (SPI). Comparative analysis using precipitation data from Türkiye shows M-SPI offers smoother transitions and more stable persistence, particularly in regions with skewed distributions.

Objective

• To introduce the Modified Standardized Precipitation Index (M-SPI) as an alternative to the Standardized Precipitation Index (SPI) for hydro-meteorological data with skewed distributions, by replacing the mean with the median in the standardization process.
• To evaluate and compare the performance of M-SPI against SPI using precipitation data from Türkiye, assessing its ability to represent drought and wetness conditions more accurately in skewed series.

Study Configuration

• Spatial Scale: Seven meteorological stations across Türkiye (e.g., Aydın, Burdur, Edirne, Rize, Çorum).
• Temporal Scale: Annual total precipitation data for the period 1966–2020, with additional applications for 3-, 6-, and 12-month accumulation windows.

Methodology and Data

• Models used: Standardized Precipitation Index (SPI), Modified Standardized Precipitation Index (M-SPI). M-SPI modifies SPI by replacing the mean with the median as the central reference in its standardization.
• Data sources: Annual total precipitation data collected from meteorological stations.

Main Results

• For near-symmetric precipitation series (e.g., Çorum), both SPI and M-SPI produce comparable outcomes.
• M-SPI tends to reveal relatively longer dry periods in regions like Aydın and Burdur.
• M-SPI indicates more extended wet periods in regions such as Edirne and Rize.
• Overall, M-SPI provides smoother drought–wetness transitions and offers a more stable representation of persistence, particularly in Mediterranean, semi-arid, and humid climates.

Contributions

• Introduces M-SPI as a novel drought index that addresses the limitations of SPI in representing precipitation conditions when distributions are skewed, by incorporating median-based standardization.
• Demonstrates that M-SPI can provide a more accurate and stable representation of drought and wetness persistence, particularly in diverse climatic regions with significant precipitation skewness.
• Offers a flexible alternative to SPI for improved drought assessment and management in regions where precipitation distributions deviate from symmetry.

Funding

[No funding information was provided in the paper text.]

Citation

@article{Gül2025Modified,
  author = {Gül, Murat and Güçlü, Yavuz Selim},
  title = {Modified standardized precipitation index for skewed hydro-meteorological data},
  journal = {Physics and Chemistry of the Earth Parts A/B/C},
  year = {2025},
  doi = {10.1016/j.pce.2025.104234},
  url = {https://doi.org/10.1016/j.pce.2025.104234}
}