Mwinjuma et al. (2025) Comparisons of SPI and SPEI in capturing drought dynamics: A Global assessment across arid and humid regions

Identification

• Journal: Atmospheric Research
• Year: 2025
• Date: 2025-09-10
• Authors: Mustafa Mwinjuma, Ren Wang, Msafiri Mtupili, Mnana Twaha
• DOI: 10.1016/j.atmosres.2025.108475

Research Groups

• State Key Laboratory for Climate System Predictions and Risk Management/Key Laboratory of Meteorological Disaster, Ministry of Education/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing, China
• School of Atmospheric Sciences, Nanjing University of Information Science and Technology, Nanjing, China
• Tanzania Meteorological Authority, Central Forecasting Office, Marine Department, Dar es Salaam, Tanzania

Short Summary

This study globally compares the Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) from 1991-2020 across diverse climatic regions, revealing that SPEI identifies significantly more frequent and severe droughts in arid and semi-arid zones due to its sensitivity to rising temperatures, challenging the adequacy of precipitation-only indices in drylands.

Objective

• To compare the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) across global arid and humid regions to systematically investigate how temperature influences drought characterization under different climatic conditions.

Study Configuration

• Spatial Scale: Global assessment across arid and humid regions.
• Temporal Scale: Period from 1991 to 2020; multi-scale analysis spanning 1- to 24-month timescales.

Methodology and Data

• Models used: Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI).
• Data sources: Gridded climate data (including precipitation and temperature for potential evapotranspiration calculation).

Main Results

• SPI and SPEI show strong agreement in humid regions (R² > 0.80), but their correlation sharply declines along the aridity gradient, reaching complete divergence (Δ = −100 %) in hyper-arid zones.
• The SPEI identifies 22–35 % more drought events than the SPI in arid/semi-arid regions, with these differences magnifying at longer timescales (24-month, r = 0.58).
• Trend analysis demonstrates that SPEI-detected drought intensification occurs twice as rapidly as SPI trends in critical agricultural zones (−0.14 vs. −0.07 standardized units per year).
• Most semi-arid regions show significantly stronger drying trends when using the SPEI.
• The SPI underestimates drought frequency by 18–27 % and severity by 1.2–2.3 standardized units in drylands.

Contributions

• Provides a systematic global assessment of the divergences between precipitation-only (SPI) and temperature-inclusive (SPEI) drought indices across varying aridity gradients.
• Quantifies the significant underestimation of drought frequency and severity by the SPI in water-limited ecosystems, highlighting its inadequacy in a warming climate.
• Emphasizes the critical need to incorporate temperature effects and weight them according to regional climatic conditions for accurate drought monitoring.
• Offers immediate implications for improving early warning systems and mitigation strategies by advocating for temperature-sensitive indices in drylands under climate change.

Funding

• Not specified in the provided text.

Citation

@article{Mwinjuma2025Comparisons,
  author = {Mwinjuma, Mustafa and Wang, Ren and Mtupili, Msafiri and Twaha, Mnana},
  title = {Comparisons of SPI and SPEI in capturing drought dynamics: A Global assessment across arid and humid regions},
  journal = {Atmospheric Research},
  year = {2025},
  doi = {10.1016/j.atmosres.2025.108475},
  url = {https://doi.org/10.1016/j.atmosres.2025.108475}
}